From a8f7a4459e45a9922483762111e4e4d08e160aa0 Mon Sep 17 00:00:00 2001 From: Joe Farebrother Date: Tue, 16 Nov 2021 13:16:03 +0000 Subject: [PATCH] Port redos libraries from Python --- .../code/java/dataflow/ExternalFlow.qll | 1 + .../lib/semmle/code/java/regex/RegexFlow.qll | 18 + .../semmle/code/java/regex/RegexTreeView.qll | 998 +++++++++++++++ java/ql/lib/semmle/code/java/regex/regex.qll | 907 +++++++++++++ .../performance/ExponentialBackTracking.qll | 342 +++++ .../java/security/performance/ReDoSUtil.qll | 1135 +++++++++++++++++ .../security/performance/RegExpTreeView.qll | 49 + .../performance/SuperlinearBackTracking.qll | 420 ++++++ 8 files changed, 3870 insertions(+) create mode 100644 java/ql/lib/semmle/code/java/regex/RegexFlow.qll create mode 100644 java/ql/lib/semmle/code/java/regex/RegexTreeView.qll create mode 100644 java/ql/lib/semmle/code/java/regex/regex.qll create mode 100644 java/ql/lib/semmle/code/java/security/performance/ExponentialBackTracking.qll create mode 100644 java/ql/lib/semmle/code/java/security/performance/ReDoSUtil.qll create mode 100644 java/ql/lib/semmle/code/java/security/performance/RegExpTreeView.qll create mode 100644 java/ql/lib/semmle/code/java/security/performance/SuperlinearBackTracking.qll diff --git a/java/ql/lib/semmle/code/java/dataflow/ExternalFlow.qll b/java/ql/lib/semmle/code/java/dataflow/ExternalFlow.qll index a6a31559260..6d14dc5f95c 100644 --- a/java/ql/lib/semmle/code/java/dataflow/ExternalFlow.qll +++ b/java/ql/lib/semmle/code/java/dataflow/ExternalFlow.qll @@ -140,6 +140,7 @@ private module Frameworks { private import semmle.code.java.frameworks.jOOQ private import semmle.code.java.frameworks.JMS private import semmle.code.java.frameworks.RabbitMQ + private import semmle.code.java.regex.RegexFlow } private predicate sourceModelCsv(string row) { diff --git a/java/ql/lib/semmle/code/java/regex/RegexFlow.qll b/java/ql/lib/semmle/code/java/regex/RegexFlow.qll new file mode 100644 index 00000000000..54b16ae8a4b --- /dev/null +++ b/java/ql/lib/semmle/code/java/regex/RegexFlow.qll @@ -0,0 +1,18 @@ +import java +import semmle.code.java.dataflow.ExternalFlow + +private class RegexSinkCsv extends SinkModelCsv { + override predicate row(string row) { + row = + [ + //"namespace;type;subtypes;name;signature;ext;input;kind" + "java.util.regex;Pattern;false;compile;(String);;Argument[0];regex-use", + "java.util.regex;Pattern;false;compile;(String,int);;Argument[0];regex-use", + "java.util.regex;Pattern;false;matches;(String,CharSequence);;Argument[0];regex-use", + "java.util;String;false;matches;(String);;Argument[0];regex-use", + "java.util;String;false;split;(String);;Argument[0];regex-use", + "java.util;String;false;split;(String,int);;Argument[0];regex-use", + "com.google.common.base;Splitter;false;onPattern;(String);;Argument[0];regex-use" + ] + } +} diff --git a/java/ql/lib/semmle/code/java/regex/RegexTreeView.qll b/java/ql/lib/semmle/code/java/regex/RegexTreeView.qll new file mode 100644 index 00000000000..1b6013b26a0 --- /dev/null +++ b/java/ql/lib/semmle/code/java/regex/RegexTreeView.qll @@ -0,0 +1,998 @@ +/** Provides a class hierarchy corresponding to a parse tree of regular expressions. */ + +import java +private import semmle.code.java.regex.regex + +/** + * An element containing a regular expression term, that is, either + * a string literal (parsed as a regular expression) + * or another regular expression term. + * + * For sequences and alternations, we require at least one child. + * Otherwise, we wish to represent the term differently. + * This avoids multiple representations of the same term. + */ +newtype TRegExpParent = + /** A string literal used as a regular expression */ + TRegExpLiteral(Regex re) or + /** A quantified term */ + TRegExpQuantifier(Regex re, int start, int end) { re.qualifiedItem(start, end, _, _) } or + /** A sequence term */ + TRegExpSequence(Regex re, int start, int end) { + re.sequence(start, end) and + exists(seqChild(re, start, end, 1)) // if a sequence does not have more than one element, it should be treated as that element instead. + } or + /** An alternation term */ + TRegExpAlt(Regex re, int start, int end) { + re.alternation(start, end) and + exists(int part_end | + re.alternationOption(start, end, start, part_end) and + part_end < end + ) // if an alternation does not have more than one element, it should be treated as that element instead. + } or + /** A character class term */ + TRegExpCharacterClass(Regex re, int start, int end) { re.charSet(start, end) } or + /** A character range term */ + TRegExpCharacterRange(Regex re, int start, int end) { re.charRange(_, start, _, _, end) } or + /** A group term */ + TRegExpGroup(Regex re, int start, int end) { re.group(start, end) } or + /** A special character */ + TRegExpSpecialChar(Regex re, int start, int end) { re.specialCharacter(start, end, _) } or + /** A normal character */ + TRegExpNormalChar(Regex re, int start, int end) { re.normalCharacter(start, end) } or + /** A back reference */ + TRegExpBackRef(Regex re, int start, int end) { re.backreference(start, end) } + +/** + * An element containing a regular expression term, that is, either + * a string literal (parsed as a regular expression) + * or another regular expression term. + */ +class RegExpParent extends TRegExpParent { + /** Gets a textual representation of this element. */ + string toString() { result = "RegExpParent" } + + /** Gets the `i`th child term. */ + abstract RegExpTerm getChild(int i); + + /** Gets a child term . */ + RegExpTerm getAChild() { result = this.getChild(_) } + + /** Gets the number of child terms. */ + int getNumChild() { result = count(this.getAChild()) } + + /** Gets the associated regex. */ + abstract Regex getRegex(); +} + +/** A string literal used as a regular expression */ +class RegExpLiteral extends TRegExpLiteral, RegExpParent { + Regex re; + + RegExpLiteral() { this = TRegExpLiteral(re) } + + override RegExpTerm getChild(int i) { i = 0 and result.getRegex() = re and result.isRootTerm() } + + /** Holds if dot, `.`, matches all characters, including newlines. */ + predicate isDotAll() { re.getAMode() = "DOTALL" } + + /** Holds if this regex matching is case-insensitive for this regex. */ + predicate isIgnoreCase() { re.getAMode() = "IGNORECASE" } + + /** Get a string representing all modes for this regex. */ + string getFlags() { result = concat(string mode | mode = re.getAMode() | mode, " | ") } + + override Regex getRegex() { result = re } + + /** Gets the primary QL class for this regex. */ + string getPrimaryQLClass() { result = "RegExpLiteral" } +} + +/** + * A regular expression term, that is, a syntactic part of a regular expression. + */ +class RegExpTerm extends RegExpParent { + Regex re; + int start; + int end; + + RegExpTerm() { + this = TRegExpAlt(re, start, end) + or + this = TRegExpBackRef(re, start, end) + or + this = TRegExpCharacterClass(re, start, end) + or + this = TRegExpCharacterRange(re, start, end) + or + this = TRegExpNormalChar(re, start, end) + or + this = TRegExpGroup(re, start, end) + or + this = TRegExpQuantifier(re, start, end) + or + this = TRegExpSequence(re, start, end) + or + this = TRegExpSpecialChar(re, start, end) + } + + /** + * Gets the outermost term of this regular expression. + */ + RegExpTerm getRootTerm() { + this.isRootTerm() and result = this + or + result = this.getParent().(RegExpTerm).getRootTerm() + } + + /** + * Holds if this term is part of a string literal + * that is interpreted as a regular expression. + */ + predicate isUsedAsRegExp() { any() } + + /** + * Holds if this is the root term of a regular expression. + */ + predicate isRootTerm() { start = 0 and end = re.getText().length() } + + override RegExpTerm getChild(int i) { + result = this.(RegExpAlt).getChild(i) + or + result = this.(RegExpBackRef).getChild(i) + or + result = this.(RegExpCharacterClass).getChild(i) + or + result = this.(RegExpCharacterRange).getChild(i) + or + result = this.(RegExpNormalChar).getChild(i) + or + result = this.(RegExpGroup).getChild(i) + or + result = this.(RegExpQuantifier).getChild(i) + or + result = this.(RegExpSequence).getChild(i) + or + result = this.(RegExpSpecialChar).getChild(i) + } + + /** + * Gets the parent term of this regular expression term, or the + * regular expression literal if this is the root term. + */ + RegExpParent getParent() { result.getAChild() = this } + + override Regex getRegex() { result = re } + + /** Gets the offset at which this term starts. */ + int getStart() { result = start } + + /** Gets the offset at which this term ends. */ + int getEnd() { result = end } + + override string toString() { result = re.getText().substring(start, end) } + + /** + * Gets the location of the surrounding regex, as locations inside the regex do not exist. + * To get location information corresponding to the term inside the regex, + * use `hasLocationInfo`. + */ + Location getLocation() { result = re.getLocation() } + + /** Holds if this term is found at the specified location offsets. */ + predicate hasLocationInfo( + string filepath, int startline, int startcolumn, int endline, int endcolumn + ) { + exists(int re_start, int re_end | + re.getLocation().hasLocationInfo(filepath, startline, re_start, endline, re_end) and + startcolumn = re_start + start + 4 and + endcolumn = re_start + end + 3 + ) + } + + /** Gets the file in which this term is found. */ + File getFile() { result = this.getLocation().getFile() } + + /** Gets the raw source text of this term. */ + string getRawValue() { result = this.toString() } + + /** Gets the string literal in which this term is found. */ + RegExpLiteral getLiteral() { result = TRegExpLiteral(re) } + + /** Gets the regular expression term that is matched (textually) before this one, if any. */ + RegExpTerm getPredecessor() { + exists(RegExpTerm parent | parent = this.getParent() | + result = parent.(RegExpSequence).previousElement(this) + or + not exists(parent.(RegExpSequence).previousElement(this)) and + not parent instanceof RegExpSubPattern and + result = parent.getPredecessor() + ) + } + + /** Gets the regular expression term that is matched (textually) after this one, if any. */ + RegExpTerm getSuccessor() { + exists(RegExpTerm parent | parent = this.getParent() | + result = parent.(RegExpSequence).nextElement(this) + or + not exists(parent.(RegExpSequence).nextElement(this)) and + not parent instanceof RegExpSubPattern and + result = parent.getSuccessor() + ) + } + + /** Gets the primary QL class for this term. */ + string getPrimaryQLClass() { result = "RegExpTerm" } +} + +/** + * A quantified regular expression term. + * + * Example: + * + * ``` + * ((ECMA|Java)[sS]cript)* + * ``` + */ +class RegExpQuantifier extends RegExpTerm, TRegExpQuantifier { + int part_end; + boolean maybe_empty; + boolean may_repeat_forever; + + RegExpQuantifier() { + this = TRegExpQuantifier(re, start, end) and + re.qualifiedPart(start, part_end, end, maybe_empty, may_repeat_forever) + } + + override RegExpTerm getChild(int i) { + i = 0 and + result.getRegex() = re and + result.getStart() = start and + result.getEnd() = part_end + } + + /** Hols if this term may match an unlimited number of times. */ + predicate mayRepeatForever() { may_repeat_forever = true } + + /** Gets the qualifier for this term. That is e.g "?" for "a?". */ + string getQualifier() { result = re.getText().substring(part_end, end) } + + override string getPrimaryQLClass() { result = "RegExpQuantifier" } +} + +/** + * A regular expression term that permits unlimited repetitions. + */ +class InfiniteRepetitionQuantifier extends RegExpQuantifier { + InfiniteRepetitionQuantifier() { this.mayRepeatForever() } +} + +/** + * A star-quantified term. + * + * Example: + * + * ``` + * \w* + * ``` + */ +class RegExpStar extends InfiniteRepetitionQuantifier { + RegExpStar() { this.getQualifier().charAt(0) = "*" } + + override string getPrimaryQLClass() { result = "RegExpStar" } +} + +/** + * A plus-quantified term. + * + * Example: + * + * ``` + * \w+ + * ``` + */ +class RegExpPlus extends InfiniteRepetitionQuantifier { + RegExpPlus() { this.getQualifier().charAt(0) = "+" } + + override string getPrimaryQLClass() { result = "RegExpPlus" } +} + +/** + * An optional term. + * + * Example: + * + * ``` + * ;? + * ``` + */ +class RegExpOpt extends RegExpQuantifier { + RegExpOpt() { this.getQualifier().charAt(0) = "?" } + + override string getPrimaryQLClass() { result = "RegExpOpt" } +} + +/** + * A range-quantified term + * + * Examples: + * + * ``` + * \w{2,4} + * \w{2,} + * \w{2} + * ``` + */ +class RegExpRange extends RegExpQuantifier { + string upper; + string lower; + + RegExpRange() { re.multiples(part_end, end, lower, upper) } + + /** Gets the string defining the upper bound of this range, if any. */ + string getUpper() { result = upper } + + /** Gets the string defining the lower bound of this range, if any. */ + string getLower() { result = lower } + + /** + * Gets the upper bound of the range, if any. + * + * If there is no upper bound, any number of repetitions is allowed. + * For a term of the form `r{lo}`, both the lower and the upper bound + * are `lo`. + */ + int getUpperBound() { result = this.getUpper().toInt() } + + /** Gets the lower bound of the range. */ + int getLowerBound() { result = this.getLower().toInt() } + + override string getPrimaryQLClass() { result = "RegExpRange" } +} + +/** + * A sequence term. + * + * Example: + * + * ``` + * (ECMA|Java)Script + * ``` + * + * This is a sequence with the elements `(ECMA|Java)` and `Script`. + */ +class RegExpSequence extends RegExpTerm, TRegExpSequence { + RegExpSequence() { this = TRegExpSequence(re, start, end) } + + override RegExpTerm getChild(int i) { result = seqChild(re, start, end, i) } + + /** Gets the element preceding `element` in this sequence. */ + RegExpTerm previousElement(RegExpTerm element) { element = this.nextElement(result) } + + /** Gets the element following `element` in this sequence. */ + RegExpTerm nextElement(RegExpTerm element) { + exists(int i | + element = this.getChild(i) and + result = this.getChild(i + 1) + ) + } + + override string getPrimaryQLClass() { result = "RegExpSequence" } +} + +pragma[nomagic] +private int seqChildEnd(Regex re, int start, int end, int i) { + result = seqChild(re, start, end, i).getEnd() +} + +// moved out so we can use it in the charpred +private RegExpTerm seqChild(Regex re, int start, int end, int i) { + re.sequence(start, end) and + ( + i = 0 and + result.getRegex() = re and + result.getStart() = start and + exists(int itemEnd | + re.item(start, itemEnd) and + result.getEnd() = itemEnd + ) + or + i > 0 and + result.getRegex() = re and + exists(int itemStart | itemStart = seqChildEnd(re, start, end, i - 1) | + result.getStart() = itemStart and + re.item(itemStart, result.getEnd()) + ) + ) +} + +/** + * An alternative term, that is, a term of the form `a|b`. + * + * Example: + * + * ``` + * ECMA|Java + * ``` + */ +class RegExpAlt extends RegExpTerm, TRegExpAlt { + RegExpAlt() { this = TRegExpAlt(re, start, end) } + + override RegExpTerm getChild(int i) { + i = 0 and + result.getRegex() = re and + result.getStart() = start and + exists(int part_end | + re.alternationOption(start, end, start, part_end) and + result.getEnd() = part_end + ) + or + i > 0 and + result.getRegex() = re and + exists(int part_start | + part_start = this.getChild(i - 1).getEnd() + 1 // allow for the | + | + result.getStart() = part_start and + re.alternationOption(start, end, part_start, result.getEnd()) + ) + } + + override string getPrimaryQLClass() { result = "RegExpAlt" } +} + +/** + * An escaped regular expression term, that is, a regular expression + * term starting with a backslash, which is not a backreference. + * + * Example: + * + * ``` + * \. + * \w + * ``` + */ +class RegExpEscape extends RegExpNormalChar { + RegExpEscape() { re.escapedCharacter(start, end) } + + /** + * Gets the name of the escaped; for example, `w` for `\w`. + * TODO: Handle named escapes. + */ + override string getValue() { + this.isIdentityEscape() and result = this.getUnescaped() + or + this.getUnescaped() = "n" and result = "\n" + or + this.getUnescaped() = "r" and result = "\r" + or + this.getUnescaped() = "t" and result = "\t" + or + // TODO: Find a way to include a formfeed character + // this.getUnescaped() = "f" and result = " " + // or + this.isUnicode() and + result = this.getUnicode() + } + + /** Holds if this terms name is given by the part following the escape character. */ + predicate isIdentityEscape() { not this.getUnescaped() in ["n", "r", "t", "f"] } + + override string getPrimaryQLClass() { result = "RegExpEscape" } + + /** Gets the part of the term following the escape character. That is e.g. "w" if the term is "\w". */ + private string getUnescaped() { result = this.getText().suffix(1) } + + /** + * Gets the text for this escape. That is e.g. "\w". + */ + private string getText() { result = re.getText().substring(start, end) } + + /** + * Holds if this is a unicode escape. + */ + private predicate isUnicode() { this.getText().prefix(2) = ["\\u", "\\U"] } + + /** + * Gets the unicode char for this escape. + * E.g. for `\u0061` this returns "a". + */ + private string getUnicode() { + exists(int codepoint | codepoint = sum(this.getHexValueFromUnicode(_)) | + result = codepoint.toUnicode() + ) + } + + /** + * Gets int value for the `index`th char in the hex number of the unicode escape. + * E.g. for `\u0061` and `index = 2` this returns 96 (the number `6` interpreted as hex). + */ + private int getHexValueFromUnicode(int index) { + this.isUnicode() and + exists(string hex, string char | hex = this.getText().suffix(2) | + char = hex.charAt(index) and + result = 16.pow(hex.length() - index - 1) * toHex(char) + ) + } +} + +/** + * Gets the hex number for the `hex` char. + */ +private int toHex(string hex) { + hex = [0 .. 9].toString() and + result = hex.toInt() + or + result = 10 and hex = ["a", "A"] + or + result = 11 and hex = ["b", "B"] + or + result = 12 and hex = ["c", "C"] + or + result = 13 and hex = ["d", "D"] + or + result = 14 and hex = ["e", "E"] + or + result = 15 and hex = ["f", "F"] +} + +/** + * A character class escape in a regular expression. + * That is, an escaped charachter that denotes multiple characters. + * + * Examples: + * + * ``` + * \w + * \S + * ``` + */ +class RegExpCharacterClassEscape extends RegExpEscape { + RegExpCharacterClassEscape() { this.getValue() in ["d", "D", "s", "S", "w", "W"] } + + override RegExpTerm getChild(int i) { none() } + + override string getPrimaryQLClass() { result = "RegExpCharacterClassEscape" } +} + +/** + * A character class in a regular expression. + * + * Examples: + * + * ``` + * [a-z_] + * [^<>&] + * ``` + */ +class RegExpCharacterClass extends RegExpTerm, TRegExpCharacterClass { + RegExpCharacterClass() { this = TRegExpCharacterClass(re, start, end) } + + /** Holds if this character class is inverted, matching the opposite of its content. */ + predicate isInverted() { re.getChar(start + 1) = "^" } + + /** Gets the `i`th char inside this charater class. */ + string getCharThing(int i) { result = re.getChar(i + start) } + + /** Holds if this character class can match anything. */ + predicate isUniversalClass() { + // [^] + this.isInverted() and not exists(this.getAChild()) + or + // [\w\W] and similar + not this.isInverted() and + exists(string cce1, string cce2 | + cce1 = this.getAChild().(RegExpCharacterClassEscape).getValue() and + cce2 = this.getAChild().(RegExpCharacterClassEscape).getValue() + | + cce1 != cce2 and cce1.toLowerCase() = cce2.toLowerCase() + ) + } + + override RegExpTerm getChild(int i) { + i = 0 and + result.getRegex() = re and + exists(int itemStart, int itemEnd | + result.getStart() = itemStart and + re.char_set_start(start, itemStart) and + re.char_set_child(start, itemStart, itemEnd) and + result.getEnd() = itemEnd + ) + or + i > 0 and + result.getRegex() = re and + exists(int itemStart | itemStart = this.getChild(i - 1).getEnd() | + result.getStart() = itemStart and + re.char_set_child(start, itemStart, result.getEnd()) + ) + } + + override string getPrimaryQLClass() { result = "RegExpCharacterClass" } +} + +/** + * A character range in a character class in a regular expression. + * + * Example: + * + * ``` + * a-z + * ``` + */ +class RegExpCharacterRange extends RegExpTerm, TRegExpCharacterRange { + int lower_end; + int upper_start; + + RegExpCharacterRange() { + this = TRegExpCharacterRange(re, start, end) and + re.charRange(_, start, lower_end, upper_start, end) + } + + /** Holds if this range goes from `lo` to `hi`, in effect is `lo-hi`. */ + predicate isRange(string lo, string hi) { + lo = re.getText().substring(start, lower_end) and + hi = re.getText().substring(upper_start, end) + } + + override RegExpTerm getChild(int i) { + i = 0 and + result.getRegex() = re and + result.getStart() = start and + result.getEnd() = lower_end + or + i = 1 and + result.getRegex() = re and + result.getStart() = upper_start and + result.getEnd() = end + } + + override string getPrimaryQLClass() { result = "RegExpCharacterRange" } +} + +/** + * A normal character in a regular expression, that is, a character + * without special meaning. This includes escaped characters. + * + * Examples: + * ``` + * t + * \t + * ``` + */ +class RegExpNormalChar extends RegExpTerm, TRegExpNormalChar { + RegExpNormalChar() { this = TRegExpNormalChar(re, start, end) } + + /** + * Holds if this constant represents a valid Unicode character (as opposed + * to a surrogate code point that does not correspond to a character by itself.) + */ + predicate isCharacter() { any() } + + /** Gets the string representation of the char matched by this term. */ + string getValue() { result = re.getText().substring(start, end) } + + override RegExpTerm getChild(int i) { none() } + + override string getPrimaryQLClass() { result = "RegExpNormalChar" } +} + +/** + * A constant regular expression term, that is, a regular expression + * term matching a single string. Currently, this will always be a single character. + * + * Example: + * + * ``` + * a + * ``` + */ +class RegExpConstant extends RegExpTerm { + string value; + + RegExpConstant() { + this = TRegExpNormalChar(re, start, end) and + not this instanceof RegExpCharacterClassEscape and + // exclude chars in qualifiers + // TODO: push this into regex library + not exists(int qstart, int qend | re.qualifiedPart(_, qstart, qend, _, _) | + qstart <= start and end <= qend + ) and + value = this.(RegExpNormalChar).getValue() + } + + /** + * Holds if this constant represents a valid Unicode character (as opposed + * to a surrogate code point that does not correspond to a character by itself.) + */ + predicate isCharacter() { any() } + + /** Gets the string matched by this constant term. */ + string getValue() { result = value } + + override RegExpTerm getChild(int i) { none() } + + override string getPrimaryQLClass() { result = "RegExpConstant" } +} + +/** + * A grouped regular expression. + * + * Examples: + * + * ``` + * (ECMA|Java) + * (?:ECMA|Java) + * (?['"]) + * ``` + */ +class RegExpGroup extends RegExpTerm, TRegExpGroup { + RegExpGroup() { this = TRegExpGroup(re, start, end) } + + /** + * Gets the index of this capture group within the enclosing regular + * expression literal. + * + * For example, in the regular expression `/((a?).)(?:b)/`, the + * group `((a?).)` has index 1, the group `(a?)` nested inside it + * has index 2, and the group `(?:b)` has no index, since it is + * not a capture group. + */ + int getNumber() { result = re.getGroupNumber(start, end) } + + /** Holds if this is a named capture group. */ + predicate isNamed() { exists(this.getName()) } + + /** Gets the name of this capture group, if any. */ + string getName() { result = re.getGroupName(start, end) } + + override RegExpTerm getChild(int i) { + result.getRegex() = re and + i = 0 and + re.groupContents(start, end, result.getStart(), result.getEnd()) + } + + override string getPrimaryQLClass() { result = "RegExpGroup" } +} + +/** + * A special character in a regular expression. + * + * Examples: + * ``` + * ^ + * $ + * . + * ``` + */ +class RegExpSpecialChar extends RegExpTerm, TRegExpSpecialChar { + string char; + + RegExpSpecialChar() { + this = TRegExpSpecialChar(re, start, end) and + re.specialCharacter(start, end, char) + } + + /** + * Holds if this constant represents a valid Unicode character (as opposed + * to a surrogate code point that does not correspond to a character by itself.) + */ + predicate isCharacter() { any() } + + /** Gets the char for this term. */ + string getChar() { result = char } + + override RegExpTerm getChild(int i) { none() } + + override string getPrimaryQLClass() { result = "RegExpSpecialChar" } +} + +/** + * A dot regular expression. + * + * Example: + * + * ``` + * . + * ``` + */ +class RegExpDot extends RegExpSpecialChar { + RegExpDot() { this.getChar() = "." } + + override string getPrimaryQLClass() { result = "RegExpDot" } +} + +/** + * A dollar assertion `$` matching the end of a line. + * + * Example: + * + * ``` + * $ + * ``` + */ +class RegExpDollar extends RegExpSpecialChar { + RegExpDollar() { this.getChar() = "$" } + + override string getPrimaryQLClass() { result = "RegExpDollar" } +} + +/** + * A caret assertion `^` matching the beginning of a line. + * + * Example: + * + * ``` + * ^ + * ``` + */ +class RegExpCaret extends RegExpSpecialChar { + RegExpCaret() { this.getChar() = "^" } + + override string getPrimaryQLClass() { result = "RegExpCaret" } +} + +/** + * A zero-width match, that is, either an empty group or an assertion. + * + * Examples: + * ``` + * () + * (?=\w) + * ``` + */ +class RegExpZeroWidthMatch extends RegExpGroup { + RegExpZeroWidthMatch() { re.zeroWidthMatch(start, end) } + + override RegExpTerm getChild(int i) { none() } + + override string getPrimaryQLClass() { result = "RegExpZeroWidthMatch" } +} + +/** + * A zero-width lookahead or lookbehind assertion. + * + * Examples: + * + * ``` + * (?=\w) + * (?!\n) + * (?<=\.) + * (?` + * in a regular expression. + * + * Examples: + * + * ``` + * \1 + * (?P=quote) + * ``` + */ +class RegExpBackRef extends RegExpTerm, TRegExpBackRef { + RegExpBackRef() { this = TRegExpBackRef(re, start, end) } + + /** + * Gets the number of the capture group this back reference refers to, if any. + */ + int getNumber() { result = re.getBackrefNumber(start, end) } + + /** + * Gets the name of the capture group this back reference refers to, if any. + */ + string getName() { result = re.getBackrefName(start, end) } + + /** Gets the capture group this back reference refers to. */ + RegExpGroup getGroup() { + result.getLiteral() = this.getLiteral() and + ( + result.getNumber() = this.getNumber() or + result.getName() = this.getName() + ) + } + + override RegExpTerm getChild(int i) { none() } + + override string getPrimaryQLClass() { result = "RegExpBackRef" } +} + +/** Gets the parse tree resulting from parsing `re`, if such has been constructed. */ +RegExpTerm getParsedRegExp(StringLiteral re) { result.getRegex() = re and result.isRootTerm() } diff --git a/java/ql/lib/semmle/code/java/regex/regex.qll b/java/ql/lib/semmle/code/java/regex/regex.qll new file mode 100644 index 00000000000..5dae7020fd9 --- /dev/null +++ b/java/ql/lib/semmle/code/java/regex/regex.qll @@ -0,0 +1,907 @@ +import java +import semmle.code.java.dataflow.DataFlow2 +import semmle.code.java.dataflow.ExternalFlow + +class RegexFlowConf extends DataFlow2::Configuration { + RegexFlowConf() { this = "RegexFlowConf" } + + override predicate isSource(DataFlow2::Node node) { node.asExpr() instanceof StringLiteral } + + override predicate isSink(DataFlow2::Node node) { sinkNode(node, "regex-use") } +} + +/** + * Holds if `s` is used as a regex, with the mode `mode` (if known). + * If regex mode is not known, `mode` will be `"None"`. + */ +predicate used_as_regex(Expr s, string mode) { + any(RegexFlowConf c).hasFlow(DataFlow2::exprNode(s), _) and + mode = "None" // TODO: proper mode detection +} + +/** + * A string literal that is used as a regular exprssion. + * TODO: adjust parser for java regex syntax + */ +abstract class RegexString extends Expr { + RegexString() { this instanceof StringLiteral } + + /** + * Helper predicate for `char_set_start(int start, int end)`. + * + * In order to identify left brackets ('[') which actually start a character class, + * we perform a left to right scan of the string. + * + * To avoid negative recursion we return a boolean. See `escaping`, + * the helper for `escapingChar`, for a clean use of this pattern. + * + * result is true for those start chars that actually mark a start of a char set. + */ + boolean char_set_start(int pos) { + exists(int index | + // is opening bracket + this.char_set_delimiter(index, pos) = true and + ( + // if this is the first bracket, `pos` starts a char set + index = 1 and result = true + or + // if the previous char set delimiter was not a closing bracket, `pos` does + // not start a char set. This is needed to handle cases such as `[[]` (a + // char set that matches the `[` char) + index > 1 and + not this.char_set_delimiter(index - 1, _) = false and + result = false + or + // special handling of cases such as `[][]` (the character-set of the characters `]` and `[`). + exists(int prev_closing_bracket_pos | + // previous bracket is a closing bracket + this.char_set_delimiter(index - 1, prev_closing_bracket_pos) = false and + if + // check if the character that comes before the previous closing bracket + // is an opening bracket (taking `^` into account) + exists(int pos_before_prev_closing_bracket | + if this.getChar(prev_closing_bracket_pos - 1) = "^" + then pos_before_prev_closing_bracket = prev_closing_bracket_pos - 2 + else pos_before_prev_closing_bracket = prev_closing_bracket_pos - 1 + | + this.char_set_delimiter(index - 2, pos_before_prev_closing_bracket) = true + ) + then + // brackets without anything in between is not valid character ranges, so + // the first closing bracket in `[]]` and `[^]]` does not count, + // + // and we should _not_ mark the second opening bracket in `[][]` and `[^][]` + // as starting a new char set. ^ ^ + exists(int pos_before_prev_closing_bracket | + this.char_set_delimiter(index - 2, pos_before_prev_closing_bracket) = true + | + result = this.char_set_start(pos_before_prev_closing_bracket).booleanNot() + ) + else + // if not, `pos` does in fact mark a real start of a character range + result = true + ) + ) + ) + } + + /** + * Helper predicate for chars that could be character-set delimiters. + * Holds if the (non-escaped) char at `pos` in the string, is the (one-based) `index` occurrence of a bracket (`[` or `]`) in the string. + * Result if `true` is the char is `[`, and `false` if the char is `]`. + */ + boolean char_set_delimiter(int index, int pos) { + pos = rank[index](int p | this.nonEscapedCharAt(p) = "[" or this.nonEscapedCharAt(p) = "]") and + ( + this.nonEscapedCharAt(pos) = "[" and result = true + or + this.nonEscapedCharAt(pos) = "]" and result = false + ) + } + + /** Hold is a character set starts between `start` and `end`. */ + predicate char_set_start(int start, int end) { + this.char_set_start(start) = true and + ( + this.getChar(start + 1) = "^" and end = start + 2 + or + not this.getChar(start + 1) = "^" and end = start + 1 + ) + } + + /** Whether there is a character class, between start (inclusive) and end (exclusive) */ + predicate charSet(int start, int end) { + exists(int inner_start, int inner_end | + this.char_set_start(start, inner_start) and + not this.char_set_start(_, start) + | + end = inner_end + 1 and + inner_end > inner_start and + this.nonEscapedCharAt(inner_end) = "]" and + not exists(int mid | this.nonEscapedCharAt(mid) = "]" | mid > inner_start and mid < inner_end) + ) + } + + /** An indexed version of `char_set_token/3` */ + private predicate char_set_token(int charset_start, int index, int token_start, int token_end) { + token_start = + rank[index](int start, int end | this.char_set_token(charset_start, start, end) | start) and + this.char_set_token(charset_start, token_start, token_end) + } + + /** Either a char or a - */ + private predicate char_set_token(int charset_start, int start, int end) { + this.char_set_start(charset_start, start) and + ( + this.escapedCharacter(start, end) + or + exists(this.nonEscapedCharAt(start)) and end = start + 1 + ) + or + this.char_set_token(charset_start, _, start) and + ( + this.escapedCharacter(start, end) + or + exists(this.nonEscapedCharAt(start)) and + end = start + 1 and + not this.getChar(start) = "]" + ) + } + + /** + * Holds if the character set starting at `charset_start` contains either + * a character or a range found between `start` and `end`. + */ + predicate char_set_child(int charset_start, int start, int end) { + this.char_set_token(charset_start, start, end) and + not exists(int range_start, int range_end | + this.charRange(charset_start, range_start, _, _, range_end) and + range_start <= start and + range_end >= end + ) + or + this.charRange(charset_start, start, _, _, end) + } + + /** + * Holds if the character set starting at `charset_start` contains a character range + * with lower bound found between `start` and `lower_end` + * and upper bound found between `upper_start` and `end`. + */ + predicate charRange(int charset_start, int start, int lower_end, int upper_start, int end) { + exists(int index | + this.charRangeEnd(charset_start, index) = true and + this.char_set_token(charset_start, index - 2, start, lower_end) and + this.char_set_token(charset_start, index, upper_start, end) + ) + } + + /** + * Helper predicate for `charRange`. + * We can determine where character ranges end by a left to right sweep. + * + * To avoid negative recursion we return a boolean. See `escaping`, + * the helper for `escapingChar`, for a clean use of this pattern. + */ + private boolean charRangeEnd(int charset_start, int index) { + this.char_set_token(charset_start, index, _, _) and + ( + index in [1, 2] and result = false + or + index > 2 and + exists(int connector_start | + this.char_set_token(charset_start, index - 1, connector_start, _) and + this.nonEscapedCharAt(connector_start) = "-" and + result = + this.charRangeEnd(charset_start, index - 2) + .booleanNot() + .booleanAnd(this.charRangeEnd(charset_start, index - 1).booleanNot()) + ) + or + not exists(int connector_start | + this.char_set_token(charset_start, index - 1, connector_start, _) and + this.nonEscapedCharAt(connector_start) = "-" + ) and + result = false + ) + } + + /** Holds if the character at `pos` is a "\" that is actually escaping what comes after. */ + predicate escapingChar(int pos) { this.escaping(pos) = true } + + /** + * Helper predicate for `escapingChar`. + * In order to avoid negative recusrion, we return a boolean. + * This way, we can refer to `escaping(pos - 1).booleanNot()` + * rather than to a negated version of `escaping(pos)`. + */ + private boolean escaping(int pos) { + pos = -1 and result = false + or + this.getChar(pos) = "\\" and result = this.escaping(pos - 1).booleanNot() + or + this.getChar(pos) != "\\" and result = false + } + + /** Gets the text of this regex */ + string getText() { result = this.(StringLiteral).getValue() } + + string getChar(int i) { result = this.getText().charAt(i) } + + string nonEscapedCharAt(int i) { + result = this.getText().charAt(i) and + not exists(int x, int y | this.escapedCharacter(x, y) and i in [x .. y - 1]) + } + + private predicate isOptionDivider(int i) { this.nonEscapedCharAt(i) = "|" } + + private predicate isGroupEnd(int i) { this.nonEscapedCharAt(i) = ")" and not this.inCharSet(i) } + + private predicate isGroupStart(int i) { this.nonEscapedCharAt(i) = "(" and not this.inCharSet(i) } + + predicate failedToParse(int i) { + exists(this.getChar(i)) and + not exists(int start, int end | + this.top_level(start, end) and + start <= i and + end > i + ) + } + + /** Named unicode characters, eg \N{degree sign} */ + private predicate escapedName(int start, int end) { + this.escapingChar(start) and + this.getChar(start + 1) = "N" and + this.getChar(start + 2) = "{" and + this.getChar(end - 1) = "}" and + end > start and + not exists(int i | start + 2 < i and i < end - 1 | this.getChar(i) = "}") + } + + /** + * Holds if an escaped character is found between `start` and `end`. + * Escaped characters include hex values, octal values and named escapes, + * but excludes backreferences. + */ + predicate escapedCharacter(int start, int end) { + this.escapingChar(start) and + not this.numbered_backreference(start, _, _) and + ( + // hex value \xhh + this.getChar(start + 1) = "x" and end = start + 4 + or + // octal value \o, \oo, or \ooo + end in [start + 2 .. start + 4] and + forall(int i | i in [start + 1 .. end - 1] | this.isOctal(i)) and + not ( + end < start + 4 and + this.isOctal(end) + ) + or + // 16-bit hex value \uhhhh + this.getChar(start + 1) = "u" and end = start + 6 + or + // 32-bit hex value \Uhhhhhhhh + this.getChar(start + 1) = "U" and end = start + 10 + or + escapedName(start, end) + or + // escape not handled above, update when adding a new case + not this.getChar(start + 1) in ["x", "u", "U", "N"] and + not exists(this.getChar(start + 1).toInt()) and + end = start + 2 + ) + } + + pragma[inline] + private predicate isOctal(int index) { this.getChar(index) = [0 .. 7].toString() } + + /** Holds if `index` is inside a character set. */ + predicate inCharSet(int index) { + exists(int x, int y | this.charSet(x, y) and index in [x + 1 .. y - 2]) + } + + /** + * 'simple' characters are any that don't alter the parsing of the regex. + */ + private predicate simpleCharacter(int start, int end) { + end = start + 1 and + not this.charSet(start, _) and + not this.charSet(_, start + 1) and + exists(string c | c = this.getChar(start) | + exists(int x, int y, int z | + this.charSet(x, z) and + this.char_set_start(x, y) + | + start = y + or + start = z - 2 + or + start > y and start < z - 2 and not this.charRange(_, _, start, end, _) + ) + or + not this.inCharSet(start) and + not c = "(" and + not c = "[" and + not c = ")" and + not c = "|" and + not this.qualifier(start, _, _, _) + ) + } + + predicate character(int start, int end) { + ( + this.simpleCharacter(start, end) and + not exists(int x, int y | this.escapedCharacter(x, y) and x <= start and y >= end) + or + this.escapedCharacter(start, end) + ) and + not exists(int x, int y | this.group_start(x, y) and x <= start and y >= end) and + not exists(int x, int y | this.backreference(x, y) and x <= start and y >= end) + } + + predicate normalCharacter(int start, int end) { + this.character(start, end) and + not this.specialCharacter(start, end, _) + } + + predicate specialCharacter(int start, int end, string char) { + this.character(start, end) and + end = start + 1 and + char = this.getChar(start) and + (char = "$" or char = "^" or char = ".") and + not this.inCharSet(start) + } + + /** Whether the text in the range start,end is a group */ + predicate group(int start, int end) { + this.groupContents(start, end, _, _) + or + this.emptyGroup(start, end) + } + + /** Gets the number of the group in start,end */ + int getGroupNumber(int start, int end) { + this.group(start, end) and + result = + count(int i | this.group(i, _) and i < start and not this.non_capturing_group_start(i, _)) + 1 + } + + /** Gets the name, if it has one, of the group in start,end */ + string getGroupName(int start, int end) { + this.group(start, end) and + exists(int name_end | + this.named_group_start(start, name_end) and + result = this.getText().substring(start + 4, name_end - 1) + ) + } + + /** Whether the text in the range start, end is a group and can match the empty string. */ + predicate zeroWidthMatch(int start, int end) { + this.emptyGroup(start, end) + or + this.negativeAssertionGroup(start, end) + or + this.positiveLookaheadAssertionGroup(start, end) + or + this.positiveLookbehindAssertionGroup(start, end) + } + + /** Holds if an empty group is found between `start` and `end`. */ + predicate emptyGroup(int start, int end) { + exists(int endm1 | end = endm1 + 1 | + this.group_start(start, endm1) and + this.isGroupEnd(endm1) + ) + } + + private predicate emptyMatchAtStartGroup(int start, int end) { + this.emptyGroup(start, end) + or + this.negativeAssertionGroup(start, end) + or + this.positiveLookaheadAssertionGroup(start, end) + } + + private predicate emptyMatchAtEndGroup(int start, int end) { + this.emptyGroup(start, end) + or + this.negativeAssertionGroup(start, end) + or + this.positiveLookbehindAssertionGroup(start, end) + } + + private predicate negativeAssertionGroup(int start, int end) { + exists(int in_start | + this.negative_lookahead_assertion_start(start, in_start) + or + this.negative_lookbehind_assertion_start(start, in_start) + | + this.groupContents(start, end, in_start, _) + ) + } + + /** Holds if a negative lookahead is found between `start` and `end` */ + predicate negativeLookaheadAssertionGroup(int start, int end) { + exists(int in_start | this.negative_lookahead_assertion_start(start, in_start) | + this.groupContents(start, end, in_start, _) + ) + } + + /** Holds if a negative lookbehind is found between `start` and `end` */ + predicate negativeLookbehindAssertionGroup(int start, int end) { + exists(int in_start | this.negative_lookbehind_assertion_start(start, in_start) | + this.groupContents(start, end, in_start, _) + ) + } + + /** Holds if a positive lookahead is found between `start` and `end` */ + predicate positiveLookaheadAssertionGroup(int start, int end) { + exists(int in_start | this.lookahead_assertion_start(start, in_start) | + this.groupContents(start, end, in_start, _) + ) + } + + /** Holds if a positive lookbehind is found between `start` and `end` */ + predicate positiveLookbehindAssertionGroup(int start, int end) { + exists(int in_start | this.lookbehind_assertion_start(start, in_start) | + this.groupContents(start, end, in_start, _) + ) + } + + private predicate group_start(int start, int end) { + this.non_capturing_group_start(start, end) + or + this.flag_group_start(start, end, _) + or + this.named_group_start(start, end) + or + this.named_backreference_start(start, end) + or + this.lookahead_assertion_start(start, end) + or + this.negative_lookahead_assertion_start(start, end) + or + this.lookbehind_assertion_start(start, end) + or + this.negative_lookbehind_assertion_start(start, end) + or + this.comment_group_start(start, end) + or + this.simple_group_start(start, end) + } + + private predicate non_capturing_group_start(int start, int end) { + this.isGroupStart(start) and + this.getChar(start + 1) = "?" and + this.getChar(start + 2) = ":" and + end = start + 3 + } + + private predicate simple_group_start(int start, int end) { + this.isGroupStart(start) and + this.getChar(start + 1) != "?" and + end = start + 1 + } + + private predicate named_group_start(int start, int end) { + this.isGroupStart(start) and + this.getChar(start + 1) = "?" and + this.getChar(start + 2) = "P" and + this.getChar(start + 3) = "<" and + not this.getChar(start + 4) = "=" and + not this.getChar(start + 4) = "!" and + exists(int name_end | + name_end = min(int i | i > start + 4 and this.getChar(i) = ">") and + end = name_end + 1 + ) + } + + private predicate named_backreference_start(int start, int end) { + this.isGroupStart(start) and + this.getChar(start + 1) = "?" and + this.getChar(start + 2) = "P" and + this.getChar(start + 3) = "=" and + // Should this be looking for unescaped ")"? + // TODO: test this + end = min(int i | i > start + 4 and this.getChar(i) = "?") + } + + private predicate flag_group_start(int start, int end, string c) { + this.isGroupStart(start) and + this.getChar(start + 1) = "?" and + end = start + 3 and + c = this.getChar(start + 2) and + c in ["i", "L", "m", "s", "u", "x"] + } + + /** + * Gets the mode of this regular expression string if + * it is defined by a prefix. + */ + string getModeFromPrefix() { + exists(string c | this.flag_group_start(_, _, c) | + c = "i" and result = "IGNORECASE" + or + c = "L" and result = "LOCALE" + or + c = "m" and result = "MULTILINE" + or + c = "s" and result = "DOTALL" + or + c = "u" and result = "UNICODE" + or + c = "x" and result = "VERBOSE" + ) + } + + private predicate lookahead_assertion_start(int start, int end) { + this.isGroupStart(start) and + this.getChar(start + 1) = "?" and + this.getChar(start + 2) = "=" and + end = start + 3 + } + + private predicate negative_lookahead_assertion_start(int start, int end) { + this.isGroupStart(start) and + this.getChar(start + 1) = "?" and + this.getChar(start + 2) = "!" and + end = start + 3 + } + + private predicate lookbehind_assertion_start(int start, int end) { + this.isGroupStart(start) and + this.getChar(start + 1) = "?" and + this.getChar(start + 2) = "<" and + this.getChar(start + 3) = "=" and + end = start + 4 + } + + private predicate negative_lookbehind_assertion_start(int start, int end) { + this.isGroupStart(start) and + this.getChar(start + 1) = "?" and + this.getChar(start + 2) = "<" and + this.getChar(start + 3) = "!" and + end = start + 4 + } + + private predicate comment_group_start(int start, int end) { + this.isGroupStart(start) and + this.getChar(start + 1) = "?" and + this.getChar(start + 2) = "#" and + end = start + 3 + } + + predicate groupContents(int start, int end, int in_start, int in_end) { + this.group_start(start, in_start) and + end = in_end + 1 and + this.top_level(in_start, in_end) and + this.isGroupEnd(in_end) + } + + private predicate named_backreference(int start, int end, string name) { + this.named_backreference_start(start, start + 4) and + end = min(int i | i > start + 4 and this.getChar(i) = ")") + 1 and + name = this.getText().substring(start + 4, end - 2) + } + + private predicate numbered_backreference(int start, int end, int value) { + this.escapingChar(start) and + // starting with 0 makes it an octal escape + not this.getChar(start + 1) = "0" and + exists(string text, string svalue, int len | + end = start + len and + text = this.getText() and + len in [2 .. 3] + | + svalue = text.substring(start + 1, start + len) and + value = svalue.toInt() and + // value is composed of digits + forall(int i | i in [start + 1 .. start + len - 1] | this.getChar(i) = [0 .. 9].toString()) and + // a longer reference is not possible + not ( + len = 2 and + exists(text.substring(start + 1, start + len + 1).toInt()) + ) and + // 3 octal digits makes it an octal escape + not forall(int i | i in [start + 1 .. start + 4] | this.isOctal(i)) + // TODO: Inside a character set, all numeric escapes are treated as characters. + ) + } + + /** Whether the text in the range start,end is a back reference */ + predicate backreference(int start, int end) { + this.numbered_backreference(start, end, _) + or + this.named_backreference(start, end, _) + } + + /** Gets the number of the back reference in start,end */ + int getBackrefNumber(int start, int end) { this.numbered_backreference(start, end, result) } + + /** Gets the name, if it has one, of the back reference in start,end */ + string getBackrefName(int start, int end) { this.named_backreference(start, end, result) } + + private predicate baseItem(int start, int end) { + this.character(start, end) and + not exists(int x, int y | this.charSet(x, y) and x <= start and y >= end) + or + this.group(start, end) + or + this.charSet(start, end) + or + this.backreference(start, end) + } + + private predicate qualifier(int start, int end, boolean maybe_empty, boolean may_repeat_forever) { + this.short_qualifier(start, end, maybe_empty, may_repeat_forever) and + not this.getChar(end) = "?" + or + exists(int short_end | this.short_qualifier(start, short_end, maybe_empty, may_repeat_forever) | + if this.getChar(short_end) = "?" then end = short_end + 1 else end = short_end + ) + } + + private predicate short_qualifier( + int start, int end, boolean maybe_empty, boolean may_repeat_forever + ) { + ( + this.getChar(start) = "+" and maybe_empty = false and may_repeat_forever = true + or + this.getChar(start) = "*" and maybe_empty = true and may_repeat_forever = true + or + this.getChar(start) = "?" and maybe_empty = true and may_repeat_forever = false + ) and + end = start + 1 + or + exists(string lower, string upper | + this.multiples(start, end, lower, upper) and + (if lower = "" or lower.toInt() = 0 then maybe_empty = true else maybe_empty = false) and + if upper = "" then may_repeat_forever = true else may_repeat_forever = false + ) + } + + /** + * Holds if a repetition quantifier is found between `start` and `end`, + * with the given lower and upper bounds. If a bound is omitted, the corresponding + * string is empty. + */ + predicate multiples(int start, int end, string lower, string upper) { + exists(string text, string match, string inner | + text = this.getText() and + end = start + match.length() and + inner = match.substring(1, match.length() - 1) + | + match = text.regexpFind("\\{[0-9]+\\}", _, start) and + lower = inner and + upper = lower + or + match = text.regexpFind("\\{[0-9]*,[0-9]*\\}", _, start) and + exists(int commaIndex | + commaIndex = inner.indexOf(",") and + lower = inner.prefix(commaIndex) and + upper = inner.suffix(commaIndex + 1) + ) + ) + } + + /** + * Whether the text in the range start,end is a qualified item, where item is a character, + * a character set or a group. + */ + predicate qualifiedItem(int start, int end, boolean maybe_empty, boolean may_repeat_forever) { + this.qualifiedPart(start, _, end, maybe_empty, may_repeat_forever) + } + + /** + * Holds if a qualified part is found between `start` and `part_end` and the qualifier is + * found between `part_end` and `end`. + * + * `maybe_empty` is true if the part is optional. + * `may_repeat_forever` is true if the part may be repeated unboundedly. + */ + predicate qualifiedPart( + int start, int part_end, int end, boolean maybe_empty, boolean may_repeat_forever + ) { + this.baseItem(start, part_end) and + this.qualifier(part_end, end, maybe_empty, may_repeat_forever) + } + + /** Holds if the range `start`, `end` contains a character, a quantifier, a character set or a group. */ + predicate item(int start, int end) { + this.qualifiedItem(start, end, _, _) + or + this.baseItem(start, end) and not this.qualifier(end, _, _, _) + } + + private predicate subsequence(int start, int end) { + ( + start = 0 or + this.group_start(_, start) or + this.isOptionDivider(start - 1) + ) and + this.item(start, end) + or + exists(int mid | + this.subsequence(start, mid) and + this.item(mid, end) + ) + } + + /** + * Whether the text in the range start,end is a sequence of 1 or more items, where an item is a character, + * a character set or a group. + */ + predicate sequence(int start, int end) { + this.sequenceOrQualified(start, end) and + not this.qualifiedItem(start, end, _, _) + } + + private predicate sequenceOrQualified(int start, int end) { + this.subsequence(start, end) and + not this.item_start(end) + } + + private predicate item_start(int start) { + this.character(start, _) or + this.isGroupStart(start) or + this.charSet(start, _) or + this.backreference(start, _) + } + + private predicate item_end(int end) { + this.character(_, end) + or + exists(int endm1 | this.isGroupEnd(endm1) and end = endm1 + 1) + or + this.charSet(_, end) + or + this.qualifier(_, end, _, _) + } + + private predicate top_level(int start, int end) { + this.subalternation(start, end, _) and + not this.isOptionDivider(end) + } + + private predicate subalternation(int start, int end, int item_start) { + this.sequenceOrQualified(start, end) and + not this.isOptionDivider(start - 1) and + item_start = start + or + start = end and + not this.item_end(start) and + this.isOptionDivider(end) and + item_start = start + or + exists(int mid | + this.subalternation(start, mid, _) and + this.isOptionDivider(mid) and + item_start = mid + 1 + | + this.sequenceOrQualified(item_start, end) + or + not this.item_start(end) and end = item_start + ) + } + + /** + * Whether the text in the range start,end is an alternation + */ + predicate alternation(int start, int end) { + this.top_level(start, end) and + exists(int less | this.subalternation(start, less, _) and less < end) + } + + /** + * Whether the text in the range start,end is an alternation and the text in part_start, part_end is one of the + * options in that alternation. + */ + predicate alternationOption(int start, int end, int part_start, int part_end) { + this.alternation(start, end) and + this.subalternation(start, part_end, part_start) + } + + /** A part of the regex that may match the start of the string. */ + private predicate firstPart(int start, int end) { + start = 0 and end = this.getText().length() + or + exists(int x | this.firstPart(x, end) | + this.emptyMatchAtStartGroup(x, start) or + this.qualifiedItem(x, start, true, _) or + this.specialCharacter(x, start, "^") + ) + or + exists(int y | this.firstPart(start, y) | + this.item(start, end) + or + this.qualifiedPart(start, end, y, _, _) + ) + or + exists(int x, int y | this.firstPart(x, y) | + this.groupContents(x, y, start, end) + or + this.alternationOption(x, y, start, end) + ) + } + + /** A part of the regex that may match the end of the string. */ + private predicate lastPart(int start, int end) { + start = 0 and end = this.getText().length() + or + exists(int y | this.lastPart(start, y) | + this.emptyMatchAtEndGroup(end, y) + or + this.qualifiedItem(end, y, true, _) + or + this.specialCharacter(end, y, "$") + or + y = end + 2 and this.escapingChar(end) and this.getChar(end + 1) = "Z" + ) + or + exists(int x | + this.lastPart(x, end) and + this.item(start, end) + ) + or + exists(int y | this.lastPart(start, y) | this.qualifiedPart(start, end, y, _, _)) + or + exists(int x, int y | this.lastPart(x, y) | + this.groupContents(x, y, start, end) + or + this.alternationOption(x, y, start, end) + ) + } + + /** + * Whether the item at [start, end) is one of the first items + * to be matched. + */ + predicate firstItem(int start, int end) { + ( + this.character(start, end) + or + this.qualifiedItem(start, end, _, _) + or + this.charSet(start, end) + ) and + this.firstPart(start, end) + } + + /** + * Whether the item at [start, end) is one of the last items + * to be matched. + */ + predicate lastItem(int start, int end) { + ( + this.character(start, end) + or + this.qualifiedItem(start, end, _, _) + or + this.charSet(start, end) + ) and + this.lastPart(start, end) + } +} + +/** A string literal used as a regular expression */ +class Regex extends RegexString { + Regex() { used_as_regex(this, _) } + + /** + * Gets a mode (if any) of this regular expression. Can be any of: + * DEBUG + * IGNORECASE + * LOCALE + * MULTILINE + * DOTALL + * UNICODE + * VERBOSE + */ + string getAMode() { + result != "None" and + used_as_regex(this, result) + or + result = this.getModeFromPrefix() + } +} diff --git a/java/ql/lib/semmle/code/java/security/performance/ExponentialBackTracking.qll b/java/ql/lib/semmle/code/java/security/performance/ExponentialBackTracking.qll new file mode 100644 index 00000000000..8d308a93104 --- /dev/null +++ b/java/ql/lib/semmle/code/java/security/performance/ExponentialBackTracking.qll @@ -0,0 +1,342 @@ +/** + * This library implements the analysis described in the following two papers: + * + * James Kirrage, Asiri Rathnayake, Hayo Thielecke: Static Analysis for + * Regular Expression Denial-of-Service Attacks. NSS 2013. + * (http://www.cs.bham.ac.uk/~hxt/research/reg-exp-sec.pdf) + * Asiri Rathnayake, Hayo Thielecke: Static Analysis for Regular Expression + * Exponential Runtime via Substructural Logics. 2014. + * (https://www.cs.bham.ac.uk/~hxt/research/redos_full.pdf) + * + * The basic idea is to search for overlapping cycles in the NFA, that is, + * states `q` such that there are two distinct paths from `q` to itself + * that consume the same word `w`. + * + * For any such state `q`, an attack string can be constructed as follows: + * concatenate a prefix `v` that takes the NFA to `q` with `n` copies of + * the word `w` that leads back to `q` along two different paths, followed + * by a suffix `x` that is _not_ accepted in state `q`. A backtracking + * implementation will need to explore at least 2^n different ways of going + * from `q` back to itself while trying to match the `n` copies of `w` + * before finally giving up. + * + * Now in order to identify overlapping cycles, all we have to do is find + * pumpable forks, that is, states `q` that can transition to two different + * states `r1` and `r2` on the same input symbol `c`, such that there are + * paths from both `r1` and `r2` to `q` that consume the same word. The latter + * condition is equivalent to saying that `(q, q)` is reachable from `(r1, r2)` + * in the product NFA. + * + * This is what the library does. It makes a simple attempt to construct a + * prefix `v` leading into `q`, but only to improve the alert message. + * And the library tries to prove the existence of a suffix that ensures + * rejection. This check might fail, which can cause false positives. + * + * Finally, sometimes it depends on the translation whether the NFA generated + * for a regular expression has a pumpable fork or not. We implement one + * particular translation, which may result in false positives or negatives + * relative to some particular JavaScript engine. + * + * More precisely, the library constructs an NFA from a regular expression `r` + * as follows: + * + * * Every sub-term `t` gives rise to an NFA state `Match(t,i)`, representing + * the state of the automaton before attempting to match the `i`th character in `t`. + * * There is one accepting state `Accept(r)`. + * * There is a special `AcceptAnySuffix(r)` state, which accepts any suffix string + * by using an epsilon transition to `Accept(r)` and an any transition to itself. + * * Transitions between states may be labelled with epsilon, or an abstract + * input symbol. + * * Each abstract input symbol represents a set of concrete input characters: + * either a single character, a set of characters represented by a + * character class, or the set of all characters. + * * The product automaton is constructed lazily, starting with pair states + * `(q, q)` where `q` is a fork, and proceding along an over-approximate + * step relation. + * * The over-approximate step relation allows transitions along pairs of + * abstract input symbols where the symbols have overlap in the characters they accept. + * * Once a trace of pairs of abstract input symbols that leads from a fork + * back to itself has been identified, we attempt to construct a concrete + * string corresponding to it, which may fail. + * * Lastly we ensure that any state reached by repeating `n` copies of `w` has + * a suffix `x` (possible empty) that is most likely __not__ accepted. + */ + +import ReDoSUtil + +/** + * Holds if state `s` might be inside a backtracking repetition. + */ +pragma[noinline] +private predicate stateInsideBacktracking(State s) { + s.getRepr().getParent*() instanceof MaybeBacktrackingRepetition +} + +/** + * A infinitely repeating quantifier that might backtrack. + */ +private class MaybeBacktrackingRepetition extends InfiniteRepetitionQuantifier { + MaybeBacktrackingRepetition() { + exists(RegExpTerm child | + child instanceof RegExpAlt or + child instanceof RegExpQuantifier + | + child.getParent+() = this + ) + } +} + +/** + * A state in the product automaton. + */ +private newtype TStatePair = + /** + * We lazily only construct those states that we are actually + * going to need: `(q, q)` for every fork state `q`, and any + * pair of states that can be reached from a pair that we have + * already constructed. To cut down on the number of states, + * we only represent states `(q1, q2)` where `q1` is lexicographically + * no bigger than `q2`. + * + * States are only constructed if both states in the pair are + * inside a repetition that might backtrack. + */ + MkStatePair(State q1, State q2) { + isFork(q1, _, _, _, _) and q2 = q1 + or + (step(_, _, _, q1, q2) or step(_, _, _, q2, q1)) and + rankState(q1) <= rankState(q2) + } + +/** + * Gets a unique number for a `state`. + * Is used to create an ordering of states, where states with the same `toString()` will be ordered differently. + */ +private int rankState(State state) { + state = + rank[result](State s, Location l | + l = s.getRepr().getLocation() + | + s order by l.getStartLine(), l.getStartColumn(), s.toString() + ) +} + +/** + * A state in the product automaton. + */ +private class StatePair extends TStatePair { + State q1; + State q2; + + StatePair() { this = MkStatePair(q1, q2) } + + /** Gets a textual representation of this element. */ + string toString() { result = "(" + q1 + ", " + q2 + ")" } + + /** Gets the first component of the state pair. */ + State getLeft() { result = q1 } + + /** Gets the second component of the state pair. */ + State getRight() { result = q2 } +} + +/** + * Holds for all constructed state pairs. + * + * Used in `statePairDist` + */ +private predicate isStatePair(StatePair p) { any() } + +/** + * Holds if there are transitions from the components of `q` to the corresponding + * components of `r`. + * + * Used in `statePairDist` + */ +private predicate delta2(StatePair q, StatePair r) { step(q, _, _, r) } + +/** + * Gets the minimum length of a path from `q` to `r` in the + * product automaton. + */ +private int statePairDist(StatePair q, StatePair r) = + shortestDistances(isStatePair/1, delta2/2)(q, r, result) + +/** + * Holds if there are transitions from `q` to `r1` and from `q` to `r2` + * labelled with `s1` and `s2`, respectively, where `s1` and `s2` do not + * trivially have an empty intersection. + * + * This predicate only holds for states associated with regular expressions + * that have at least one repetition quantifier in them (otherwise the + * expression cannot be vulnerable to ReDoS attacks anyway). + */ +pragma[noopt] +private predicate isFork(State q, InputSymbol s1, InputSymbol s2, State r1, State r2) { + stateInsideBacktracking(q) and + exists(State q1, State q2 | + q1 = epsilonSucc*(q) and + delta(q1, s1, r1) and + q2 = epsilonSucc*(q) and + delta(q2, s2, r2) and + // Use pragma[noopt] to prevent intersect(s1,s2) from being the starting point of the join. + // From (s1,s2) it would find a huge number of intermediate state pairs (q1,q2) originating from different literals, + // and discover at the end that no `q` can reach both `q1` and `q2` by epsilon transitions. + exists(intersect(s1, s2)) + | + s1 != s2 + or + r1 != r2 + or + r1 = r2 and q1 != q2 + or + // If q can reach itself by epsilon transitions, then there are two distinct paths to the q1/q2 state: + // one that uses the loop and one that doesn't. The engine will separately attempt to match with each path, + // despite ending in the same state. The "fork" thus arises from the choice of whether to use the loop or not. + // To avoid every state in the loop becoming a fork state, + // we arbitrarily pick the InfiniteRepetitionQuantifier state as the canonical fork state for the loop + // (every epsilon-loop must contain such a state). + // + // We additionally require that the there exists another InfiniteRepetitionQuantifier `mid` on the path from `q` to itself. + // This is done to avoid flagging regular expressions such as `/(a?)*b/` - that only has polynomial runtime, and is detected by `js/polynomial-redos`. + // The below code is therefore a heuritic, that only flags regular expressions such as `/(a*)*b/`, + // and does not flag regular expressions such as `/(a?b?)c/`, but the latter pattern is not used frequently. + r1 = r2 and + q1 = q2 and + epsilonSucc+(q) = q and + exists(RegExpTerm term | term = q.getRepr() | term instanceof InfiniteRepetitionQuantifier) and + // One of the mid states is an infinite quantifier itself + exists(State mid, RegExpTerm term | + mid = epsilonSucc+(q) and + term = mid.getRepr() and + term instanceof InfiniteRepetitionQuantifier and + q = epsilonSucc+(mid) and + not mid = q + ) + ) and + stateInsideBacktracking(r1) and + stateInsideBacktracking(r2) +} + +/** + * Gets the state pair `(q1, q2)` or `(q2, q1)`; note that only + * one or the other is defined. + */ +private StatePair mkStatePair(State q1, State q2) { + result = MkStatePair(q1, q2) or result = MkStatePair(q2, q1) +} + +/** + * Holds if there are transitions from the components of `q` to the corresponding + * components of `r` labelled with `s1` and `s2`, respectively. + */ +private predicate step(StatePair q, InputSymbol s1, InputSymbol s2, StatePair r) { + exists(State r1, State r2 | step(q, s1, s2, r1, r2) and r = mkStatePair(r1, r2)) +} + +/** + * Holds if there are transitions from the components of `q` to `r1` and `r2` + * labelled with `s1` and `s2`, respectively. + * + * We only consider transitions where the resulting states `(r1, r2)` are both + * inside a repetition that might backtrack. + */ +pragma[noopt] +private predicate step(StatePair q, InputSymbol s1, InputSymbol s2, State r1, State r2) { + exists(State q1, State q2 | q.getLeft() = q1 and q.getRight() = q2 | + deltaClosed(q1, s1, r1) and + deltaClosed(q2, s2, r2) and + // use noopt to force the join on `intersect` to happen last. + exists(intersect(s1, s2)) + ) and + stateInsideBacktracking(r1) and + stateInsideBacktracking(r2) +} + +private newtype TTrace = + Nil() or + Step(InputSymbol s1, InputSymbol s2, TTrace t) { + exists(StatePair p | + isReachableFromFork(_, p, t, _) and + step(p, s1, s2, _) + ) + or + t = Nil() and isFork(_, s1, s2, _, _) + } + +/** + * A list of pairs of input symbols that describe a path in the product automaton + * starting from some fork state. + */ +private class Trace extends TTrace { + /** Gets a textual representation of this element. */ + string toString() { + this = Nil() and result = "Nil()" + or + exists(InputSymbol s1, InputSymbol s2, Trace t | this = Step(s1, s2, t) | + result = "Step(" + s1 + ", " + s2 + ", " + t + ")" + ) + } +} + +/** + * Gets a string corresponding to the trace `t`. + */ +private string concretise(Trace t) { + t = Nil() and result = "" + or + exists(InputSymbol s1, InputSymbol s2, Trace rest | t = Step(s1, s2, rest) | + result = concretise(rest) + intersect(s1, s2) + ) +} + +/** + * Holds if `r` is reachable from `(fork, fork)` under input `w`, and there is + * a path from `r` back to `(fork, fork)` with `rem` steps. + */ +private predicate isReachableFromFork(State fork, StatePair r, Trace w, int rem) { + // base case + exists(InputSymbol s1, InputSymbol s2, State q1, State q2 | + isFork(fork, s1, s2, q1, q2) and + r = MkStatePair(q1, q2) and + w = Step(s1, s2, Nil()) and + rem = statePairDist(r, MkStatePair(fork, fork)) + ) + or + // recursive case + exists(StatePair p, Trace v, InputSymbol s1, InputSymbol s2 | + isReachableFromFork(fork, p, v, rem + 1) and + step(p, s1, s2, r) and + w = Step(s1, s2, v) and + rem >= statePairDist(r, MkStatePair(fork, fork)) + ) +} + +/** + * Gets a state in the product automaton from which `(fork, fork)` is + * reachable in zero or more epsilon transitions. + */ +private StatePair getAForkPair(State fork) { + isFork(fork, _, _, _, _) and + result = MkStatePair(epsilonPred*(fork), epsilonPred*(fork)) +} + +/** + * Holds if `fork` is a pumpable fork with word `w`. + */ +private predicate isPumpable(State fork, string w) { + exists(StatePair q, Trace t | + isReachableFromFork(fork, q, t, _) and + q = getAForkPair(fork) and + w = concretise(t) + ) +} + +/** + * An instantiation of `ReDoSConfiguration` for exponential backtracking. + */ +class ExponentialReDoSConfiguration extends ReDoSConfiguration { + ExponentialReDoSConfiguration() { this = "ExponentialReDoSConfiguration" } + + override predicate isReDoSCandidate(State state, string pump) { isPumpable(state, pump) } +} diff --git a/java/ql/lib/semmle/code/java/security/performance/ReDoSUtil.qll b/java/ql/lib/semmle/code/java/security/performance/ReDoSUtil.qll new file mode 100644 index 00000000000..2cd324ed8f7 --- /dev/null +++ b/java/ql/lib/semmle/code/java/security/performance/ReDoSUtil.qll @@ -0,0 +1,1135 @@ +/** + * Provides classes for working with regular expressions that can + * perform backtracking in superlinear/exponential time. + * + * This module contains a number of utility predicates for compiling a regular expression into a NFA and reasoning about this NFA. + * + * The `ReDoSConfiguration` contains a `isReDoSCandidate` predicate that is used to + * to determine which states the prefix/suffix search should happen on. + * There is only meant to exist one `ReDoSConfiguration` at a time. + * + * The predicate `hasReDoSResult` outputs a de-duplicated set of + * states that will cause backtracking (a rejecting suffix exists). + */ + +import RegExpTreeView + +/** + * A configuration for which parts of a regular expression should be considered relevant for + * the different predicates in `ReDoS.qll`. + * Used to adjust the computations for either superlinear or exponential backtracking. + */ +abstract class ReDoSConfiguration extends string { + bindingset[this] + ReDoSConfiguration() { any() } + + /** + * Holds if `state` with the pump string `pump` is a candidate for a + * ReDoS vulnerable state. + * This is used to determine which states are considered for the prefix/suffix construction. + */ + abstract predicate isReDoSCandidate(State state, string pump); +} + +/** + * Holds if repeating `pump' starting at `state` is a candidate for causing backtracking. + * No check whether a rejected suffix exists has been made. + */ +private predicate isReDoSCandidate(State state, string pump) { + any(ReDoSConfiguration conf).isReDoSCandidate(state, pump) and + ( + not any(ReDoSConfiguration conf).isReDoSCandidate(epsilonSucc+(state), _) + or + epsilonSucc+(state) = state and + state = + max(State s, Location l | + s = epsilonSucc+(state) and + l = s.getRepr().getLocation() and + any(ReDoSConfiguration conf).isReDoSCandidate(s, _) and + s.getRepr() instanceof InfiniteRepetitionQuantifier + | + s order by l.getStartLine(), l.getStartColumn(), l.getEndColumn(), l.getEndLine() + ) + ) +} + +/** + * Gets the char after `c` (from a simplified ASCII table). + */ +private string nextChar(string c) { exists(int code | code = ascii(c) | code + 1 = ascii(result)) } + +/** + * Gets an approximation for the ASCII code for `char`. + * Only the easily printable chars are included (so no newline, tab, null, etc). + */ +private int ascii(string char) { + char = + rank[result](string c | + c = + "! \"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|}~" + .charAt(_) + ) +} + +/** + * Holds if `t` matches at least an epsilon symbol. + * + * That is, this term does not restrict the language of the enclosing regular expression. + * + * This is implemented as an under-approximation, and this predicate does not hold for sub-patterns in particular. + */ +predicate matchesEpsilon(RegExpTerm t) { + t instanceof RegExpStar + or + t instanceof RegExpOpt + or + t.(RegExpRange).getLowerBound() = 0 + or + exists(RegExpTerm child | + child = t.getAChild() and + matchesEpsilon(child) + | + t instanceof RegExpAlt or + t instanceof RegExpGroup or + t instanceof RegExpPlus or + t instanceof RegExpRange + ) + or + matchesEpsilon(t.(RegExpBackRef).getGroup()) + or + forex(RegExpTerm child | child = t.(RegExpSequence).getAChild() | matchesEpsilon(child)) +} + +/** + * A lookahead/lookbehind that matches the empty string. + */ +class EmptyPositiveSubPatttern extends RegExpSubPattern { + EmptyPositiveSubPatttern() { + ( + this instanceof RegExpPositiveLookahead + or + this instanceof RegExpPositiveLookbehind + ) and + matchesEpsilon(this.getOperand()) + } +} + +/** + * A branch in a disjunction that is the root node in a literal, or a literal + * whose root node is not a disjunction. + */ +class RegExpRoot extends RegExpTerm { + RegExpParent parent; + + RegExpRoot() { + exists(RegExpAlt alt | + alt.isRootTerm() and + this = alt.getAChild() and + parent = alt.getParent() + ) + or + this.isRootTerm() and + not this instanceof RegExpAlt and + parent = this.getParent() + } + + /** + * Holds if this root term is relevant to the ReDoS analysis. + */ + predicate isRelevant() { + // there is at least one repetition + getRoot(any(InfiniteRepetitionQuantifier q)) = this and + // is actually used as a RegExp + isUsedAsRegExp() and + // not excluded for library specific reasons + not isExcluded(getRootTerm().getParent()) + } +} + +/** + * A constant in a regular expression that represents valid Unicode character(s). + */ +private class RegexpCharacterConstant extends RegExpConstant { + RegexpCharacterConstant() { this.isCharacter() } +} + +/** + * A regexp term that is relevant for this ReDoS analysis. + */ +class RelevantRegExpTerm extends RegExpTerm { + RelevantRegExpTerm() { getRoot(this).isRelevant() } +} + +/** + * Holds if `term` is the chosen canonical representative for all terms with string representation `str`. + * The string representation includes which flags are used with the regular expression. + * + * Using canonical representatives gives a huge performance boost when working with tuples containing multiple `InputSymbol`s. + * The number of `InputSymbol`s is decreased by 3 orders of magnitude or more in some larger benchmarks. + */ +private predicate isCanonicalTerm(RelevantRegExpTerm term, string str) { + term = + min(RelevantRegExpTerm t, Location loc, File file | + loc = t.getLocation() and + file = t.getFile() and + str = t.getRawValue() + "|" + getCanonicalizationFlags(t.getRootTerm()) + | + t order by t.getFile().getRelativePath(), loc.getStartLine(), loc.getStartColumn() + ) +} + +/** + * Gets a string reperesentation of the flags used with the regular expression. + * Only the flags that are relevant for the canonicalization are included. + */ +string getCanonicalizationFlags(RegExpTerm root) { + root.isRootTerm() and + (if RegExpFlags::isIgnoreCase(root) then result = "i" else result = "") +} + +/** + * An abstract input symbol, representing a set of concrete characters. + */ +private newtype TInputSymbol = + /** An input symbol corresponding to character `c`. */ + Char(string c) { + c = + any(RegexpCharacterConstant cc | + cc instanceof RelevantRegExpTerm and + not RegExpFlags::isIgnoreCase(cc.getRootTerm()) + ).getValue().charAt(_) + or + // normalize everything to lower case if the regexp is case insensitive + c = + any(RegexpCharacterConstant cc, string char | + cc instanceof RelevantRegExpTerm and + RegExpFlags::isIgnoreCase(cc.getRootTerm()) and + char = cc.getValue().charAt(_) + | + char.toLowerCase() + ) + } or + /** + * An input symbol representing all characters matched by + * a (non-universal) character class that has string representation `charClassString`. + */ + CharClass(string charClassString) { + exists(RelevantRegExpTerm recc | isCanonicalTerm(recc, charClassString) | + recc instanceof RegExpCharacterClass and + not recc.(RegExpCharacterClass).isUniversalClass() + or + recc instanceof RegExpCharacterClassEscape + ) + } or + /** An input symbol representing all characters matched by `.`. */ + Dot() or + /** An input symbol representing all characters. */ + Any() or + /** An epsilon transition in the automaton. */ + Epsilon() + +/** + * Gets the canonical CharClass for `term`. + */ +CharClass getCanonicalCharClass(RegExpTerm term) { + exists(string str | isCanonicalTerm(term, str) | result = CharClass(str)) +} + +/** + * Holds if `a` and `b` are input symbols from the same regexp. + */ +private predicate sharesRoot(TInputSymbol a, TInputSymbol b) { + exists(RegExpRoot root | + belongsTo(a, root) and + belongsTo(b, root) + ) +} + +/** + * Holds if the `a` is an input symbol from a regexp that has root `root`. + */ +private predicate belongsTo(TInputSymbol a, RegExpRoot root) { + exists(State s | getRoot(s.getRepr()) = root | + delta(s, a, _) + or + delta(_, a, s) + ) +} + +/** + * An abstract input symbol, representing a set of concrete characters. + */ +class InputSymbol extends TInputSymbol { + InputSymbol() { not this instanceof Epsilon } + + /** + * Gets a string representation of this input symbol. + */ + string toString() { + this = Char(result) + or + this = CharClass(result) + or + this = Dot() and result = "." + or + this = Any() and result = "[^]" + } +} + +/** + * An abstract input symbol that represents a character class. + */ +abstract class CharacterClass extends InputSymbol { + /** + * Gets a character that is relevant for intersection-tests involving this + * character class. + * + * Specifically, this is any of the characters mentioned explicitly in the + * character class, offset by one if it is inverted. For character class escapes, + * the result is as if the class had been written out as a series of intervals. + * + * This set is large enough to ensure that for any two intersecting character + * classes, one contains a relevant character from the other. + */ + abstract string getARelevantChar(); + + /** + * Holds if this character class matches `char`. + */ + bindingset[char] + abstract predicate matches(string char); + + /** + * Gets a character matched by this character class. + */ + string choose() { result = getARelevantChar() and matches(result) } +} + +/** + * Provides implementations for `CharacterClass`. + */ +private module CharacterClasses { + /** + * Holds if the character class `cc` has a child (constant or range) that matches `char`. + */ + pragma[noinline] + predicate hasChildThatMatches(RegExpCharacterClass cc, string char) { + if RegExpFlags::isIgnoreCase(cc.getRootTerm()) + then + // normalize everything to lower case if the regexp is case insensitive + exists(string c | hasChildThatMatchesIgnoringCasingFlags(cc, c) | char = c.toLowerCase()) + else hasChildThatMatchesIgnoringCasingFlags(cc, char) + } + + /** + * Holds if the character class `cc` has a child (constant or range) that matches `char`. + * Ignores whether the character class is inside a regular expression that has the ignore case flag. + */ + pragma[noinline] + predicate hasChildThatMatchesIgnoringCasingFlags(RegExpCharacterClass cc, string char) { + exists(getCanonicalCharClass(cc)) and + exists(RegExpTerm child | child = cc.getAChild() | + char = child.(RegexpCharacterConstant).getValue() + or + rangeMatchesOnLetterOrDigits(child, char) + or + not rangeMatchesOnLetterOrDigits(child, _) and + char = getARelevantChar() and + exists(string lo, string hi | child.(RegExpCharacterRange).isRange(lo, hi) | + lo <= char and + char <= hi + ) + or + exists(RegExpCharacterClassEscape escape | escape = child | + escape.getValue() = escape.getValue().toLowerCase() and + classEscapeMatches(escape.getValue(), char) + or + char = getARelevantChar() and + escape.getValue() = escape.getValue().toUpperCase() and + not classEscapeMatches(escape.getValue().toLowerCase(), char) + ) + ) + } + + /** + * Holds if `range` is a range on lower-case, upper-case, or digits, and matches `char`. + * This predicate is used to restrict the searchspace for ranges by only joining `getAnyPossiblyMatchedChar` + * on a few ranges. + */ + private predicate rangeMatchesOnLetterOrDigits(RegExpCharacterRange range, string char) { + exists(string lo, string hi | + range.isRange(lo, hi) and lo = lowercaseLetter() and hi = lowercaseLetter() + | + lo <= char and + char <= hi and + char = lowercaseLetter() + ) + or + exists(string lo, string hi | + range.isRange(lo, hi) and lo = upperCaseLetter() and hi = upperCaseLetter() + | + lo <= char and + char <= hi and + char = upperCaseLetter() + ) + or + exists(string lo, string hi | range.isRange(lo, hi) and lo = digit() and hi = digit() | + lo <= char and + char <= hi and + char = digit() + ) + } + + private string lowercaseLetter() { result = "abdcefghijklmnopqrstuvwxyz".charAt(_) } + + private string upperCaseLetter() { result = "ABCDEFGHIJKLMNOPQRSTUVWXYZ".charAt(_) } + + private string digit() { result = [0 .. 9].toString() } + + /** + * Gets a char that could be matched by a regular expression. + * Includes all printable ascii chars, all constants mentioned in a regexp, and all chars matches by the regexp `/\s|\d|\w/`. + */ + string getARelevantChar() { + exists(ascii(result)) + or + exists(RegexpCharacterConstant c | result = c.getValue().charAt(_)) + or + classEscapeMatches(_, result) + } + + /** + * Gets a char that is mentioned in the character class `c`. + */ + private string getAMentionedChar(RegExpCharacterClass c) { + exists(RegExpTerm child | child = c.getAChild() | + result = child.(RegexpCharacterConstant).getValue() + or + child.(RegExpCharacterRange).isRange(result, _) + or + child.(RegExpCharacterRange).isRange(_, result) + or + exists(RegExpCharacterClassEscape escape | child = escape | + result = min(string s | classEscapeMatches(escape.getValue().toLowerCase(), s)) + or + result = max(string s | classEscapeMatches(escape.getValue().toLowerCase(), s)) + ) + ) + } + + /** + * An implementation of `CharacterClass` for positive (non inverted) character classes. + */ + private class PositiveCharacterClass extends CharacterClass { + RegExpCharacterClass cc; + + PositiveCharacterClass() { this = getCanonicalCharClass(cc) and not cc.isInverted() } + + override string getARelevantChar() { result = getAMentionedChar(cc) } + + override predicate matches(string char) { hasChildThatMatches(cc, char) } + } + + /** + * An implementation of `CharacterClass` for inverted character classes. + */ + private class InvertedCharacterClass extends CharacterClass { + RegExpCharacterClass cc; + + InvertedCharacterClass() { this = getCanonicalCharClass(cc) and cc.isInverted() } + + override string getARelevantChar() { + result = nextChar(getAMentionedChar(cc)) or + nextChar(result) = getAMentionedChar(cc) + } + + bindingset[char] + override predicate matches(string char) { not hasChildThatMatches(cc, char) } + } + + /** + * Holds if the character class escape `clazz` (\d, \s, or \w) matches `char`. + */ + pragma[noinline] + private predicate classEscapeMatches(string clazz, string char) { + clazz = "d" and + char = "0123456789".charAt(_) + or + clazz = "s" and + char = [" ", "\t", "\r", "\n", 11.toUnicode(), 12.toUnicode()] // 11.toUnicode() = \v, 12.toUnicode() = \f + or + clazz = "w" and + char = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_".charAt(_) + } + + /** + * An implementation of `CharacterClass` for \d, \s, and \w. + */ + private class PositiveCharacterClassEscape extends CharacterClass { + RegExpCharacterClassEscape cc; + + PositiveCharacterClassEscape() { + this = getCanonicalCharClass(cc) and cc.getValue() = ["d", "s", "w"] + } + + override string getARelevantChar() { + cc.getValue() = "d" and + result = ["0", "9"] + or + cc.getValue() = "s" and + result = " " + or + cc.getValue() = "w" and + result = ["a", "Z", "_", "0", "9"] + } + + override predicate matches(string char) { classEscapeMatches(cc.getValue(), char) } + + override string choose() { + cc.getValue() = "d" and + result = "9" + or + cc.getValue() = "s" and + result = " " + or + cc.getValue() = "w" and + result = "a" + } + } + + /** + * An implementation of `CharacterClass` for \D, \S, and \W. + */ + private class NegativeCharacterClassEscape extends CharacterClass { + RegExpCharacterClassEscape cc; + + NegativeCharacterClassEscape() { + this = getCanonicalCharClass(cc) and cc.getValue() = ["D", "S", "W"] + } + + override string getARelevantChar() { + cc.getValue() = "D" and + result = ["a", "Z", "!"] + or + cc.getValue() = "S" and + result = ["a", "9", "!"] + or + cc.getValue() = "W" and + result = [" ", "!"] + } + + bindingset[char] + override predicate matches(string char) { + not classEscapeMatches(cc.getValue().toLowerCase(), char) + } + } +} + +private class EdgeLabel extends TInputSymbol { + string toString() { + this = Epsilon() and result = "" + or + exists(InputSymbol s | this = s and result = s.toString()) + } +} + +/** + * Gets the state before matching `t`. + */ +pragma[inline] +private State before(RegExpTerm t) { result = Match(t, 0) } + +/** + * Gets a state the NFA may be in after matching `t`. + */ +private State after(RegExpTerm t) { + exists(RegExpAlt alt | t = alt.getAChild() | result = after(alt)) + or + exists(RegExpSequence seq, int i | t = seq.getChild(i) | + result = before(seq.getChild(i + 1)) + or + i + 1 = seq.getNumChild() and result = after(seq) + ) + or + exists(RegExpGroup grp | t = grp.getAChild() | result = after(grp)) + or + exists(RegExpStar star | t = star.getAChild() | result = before(star)) + or + exists(RegExpPlus plus | t = plus.getAChild() | + result = before(plus) or + result = after(plus) + ) + or + exists(RegExpOpt opt | t = opt.getAChild() | result = after(opt)) + or + exists(RegExpRoot root | t = root | result = AcceptAnySuffix(root)) +} + +/** + * Holds if the NFA has a transition from `q1` to `q2` labelled with `lbl`. + */ +predicate delta(State q1, EdgeLabel lbl, State q2) { + exists(RegexpCharacterConstant s, int i | + q1 = Match(s, i) and + ( + not RegExpFlags::isIgnoreCase(s.getRootTerm()) and + lbl = Char(s.getValue().charAt(i)) + or + // normalize everything to lower case if the regexp is case insensitive + RegExpFlags::isIgnoreCase(s.getRootTerm()) and + exists(string c | c = s.getValue().charAt(i) | lbl = Char(c.toLowerCase())) + ) and + ( + q2 = Match(s, i + 1) + or + s.getValue().length() = i + 1 and + q2 = after(s) + ) + ) + or + exists(RegExpDot dot | q1 = before(dot) and q2 = after(dot) | + if RegExpFlags::isDotAll(dot.getRootTerm()) then lbl = Any() else lbl = Dot() + ) + or + exists(RegExpCharacterClass cc | + cc.isUniversalClass() and q1 = before(cc) and lbl = Any() and q2 = after(cc) + or + q1 = before(cc) and + lbl = CharClass(cc.getRawValue() + "|" + getCanonicalizationFlags(cc.getRootTerm())) and + q2 = after(cc) + ) + or + exists(RegExpCharacterClassEscape cc | + q1 = before(cc) and + lbl = CharClass(cc.getRawValue() + "|" + getCanonicalizationFlags(cc.getRootTerm())) and + q2 = after(cc) + ) + or + exists(RegExpAlt alt | lbl = Epsilon() | q1 = before(alt) and q2 = before(alt.getAChild())) + or + exists(RegExpSequence seq | lbl = Epsilon() | q1 = before(seq) and q2 = before(seq.getChild(0))) + or + exists(RegExpGroup grp | lbl = Epsilon() | q1 = before(grp) and q2 = before(grp.getChild(0))) + or + exists(RegExpStar star | lbl = Epsilon() | + q1 = before(star) and q2 = before(star.getChild(0)) + or + q1 = before(star) and q2 = after(star) + ) + or + exists(RegExpPlus plus | lbl = Epsilon() | q1 = before(plus) and q2 = before(plus.getChild(0))) + or + exists(RegExpOpt opt | lbl = Epsilon() | + q1 = before(opt) and q2 = before(opt.getChild(0)) + or + q1 = before(opt) and q2 = after(opt) + ) + or + exists(RegExpRoot root | q1 = AcceptAnySuffix(root) | + lbl = Any() and q2 = q1 + or + lbl = Epsilon() and q2 = Accept(root) + ) + or + exists(RegExpRoot root | q1 = Match(root, 0) | lbl = Any() and q2 = q1) + or + exists(RegExpDollar dollar | q1 = before(dollar) | + lbl = Epsilon() and q2 = Accept(getRoot(dollar)) + ) + or + exists(EmptyPositiveSubPatttern empty | q1 = before(empty) | + lbl = Epsilon() and q2 = after(empty) + ) +} + +/** + * Gets a state that `q` has an epsilon transition to. + */ +State epsilonSucc(State q) { delta(q, Epsilon(), result) } + +/** + * Gets a state that has an epsilon transition to `q`. + */ +State epsilonPred(State q) { q = epsilonSucc(result) } + +/** + * Holds if there is a state `q` that can be reached from `q1` + * along epsilon edges, such that there is a transition from + * `q` to `q2` that consumes symbol `s`. + */ +predicate deltaClosed(State q1, InputSymbol s, State q2) { delta(epsilonSucc*(q1), s, q2) } + +/** + * Gets the root containing the given term, that is, the root of the literal, + * or a branch of the root disjunction. + */ +RegExpRoot getRoot(RegExpTerm term) { + result = term or + result = getRoot(term.getParent()) +} + +/** + * A state in the NFA. + */ +private newtype TState = + /** + * A state representing that the NFA is about to match a term. + * `i` is used to index into multi-char literals. + */ + Match(RelevantRegExpTerm t, int i) { + i = 0 + or + exists(t.(RegexpCharacterConstant).getValue().charAt(i)) + } or + /** + * An accept state, where exactly the given input string is accepted. + */ + Accept(RegExpRoot l) { l.isRelevant() } or + /** + * An accept state, where the given input string, or any string that has this + * string as a prefix, is accepted. + */ + AcceptAnySuffix(RegExpRoot l) { l.isRelevant() } + +/** + * Gets a state that is about to match the regular expression `t`. + */ +State mkMatch(RegExpTerm t) { result = Match(t, 0) } + +/** + * A state in the NFA corresponding to a regular expression. + * + * Each regular expression literal `l` has one accepting state + * `Accept(l)`, one state that accepts all suffixes `AcceptAnySuffix(l)`, + * and a state `Match(t, i)` for every subterm `t`, + * which represents the state of the NFA before starting to + * match `t`, or the `i`th character in `t` if `t` is a constant. + */ +class State extends TState { + RegExpTerm repr; + + State() { + this = Match(repr, _) or + this = Accept(repr) or + this = AcceptAnySuffix(repr) + } + + /** + * Gets a string representation for this state in a regular expression. + */ + string toString() { + exists(int i | this = Match(repr, i) | result = "Match(" + repr + "," + i + ")") + or + this instanceof Accept and + result = "Accept(" + repr + ")" + or + this instanceof AcceptAnySuffix and + result = "AcceptAny(" + repr + ")" + } + + /** + * Gets the location for this state. + */ + Location getLocation() { result = repr.getLocation() } + + /** + * Gets the term represented by this state. + */ + RegExpTerm getRepr() { result = repr } +} + +/** + * Gets the minimum char that is matched by both the character classes `c` and `d`. + */ +private string getMinOverlapBetweenCharacterClasses(CharacterClass c, CharacterClass d) { + result = min(getAOverlapBetweenCharacterClasses(c, d)) +} + +/** + * Gets a char that is matched by both the character classes `c` and `d`. + * And `c` and `d` is not the same character class. + */ +private string getAOverlapBetweenCharacterClasses(CharacterClass c, CharacterClass d) { + sharesRoot(c, d) and + result = [c.getARelevantChar(), d.getARelevantChar()] and + c.matches(result) and + d.matches(result) and + not c = d +} + +/** + * Gets a character that is represented by both `c` and `d`. + */ +string intersect(InputSymbol c, InputSymbol d) { + (sharesRoot(c, d) or [c, d] = Any()) and + ( + c = Char(result) and + d = getAnInputSymbolMatching(result) + or + result = getMinOverlapBetweenCharacterClasses(c, d) + or + result = c.(CharacterClass).choose() and + ( + d = c + or + d = Dot() and + not (result = "\n" or result = "\r") + or + d = Any() + ) + or + (c = Dot() or c = Any()) and + (d = Dot() or d = Any()) and + result = "a" + ) + or + result = intersect(d, c) +} + +/** + * Gets a symbol that matches `char`. + */ +bindingset[char] +InputSymbol getAnInputSymbolMatching(string char) { + result = Char(char) + or + result.(CharacterClass).matches(char) + or + result = Dot() and + not (char = "\n" or char = "\r") + or + result = Any() +} + +/** + * Predicates for constructing a prefix string that leads to a given state. + */ +private module PrefixConstruction { + /** + * Holds if `state` starts the string matched by the regular expression. + */ + private predicate isStartState(State state) { + state instanceof StateInPumpableRegexp and + ( + state = Match(any(RegExpRoot r), _) + or + exists(RegExpCaret car | state = after(car)) + ) + } + + /** + * Holds if `state` is the textually last start state for the regular expression. + */ + private predicate lastStartState(State state) { + exists(RegExpRoot root | + state = + max(State s, Location l | + isStartState(s) and getRoot(s.getRepr()) = root and l = s.getRepr().getLocation() + | + s + order by + l.getStartLine(), l.getStartColumn(), s.getRepr().toString(), l.getEndColumn(), + l.getEndLine() + ) + ) + } + + /** + * Holds if there exists any transition (Epsilon() or other) from `a` to `b`. + */ + private predicate existsTransition(State a, State b) { delta(a, _, b) } + + /** + * Gets the minimum number of transitions it takes to reach `state` from the `start` state. + */ + int prefixLength(State start, State state) = + shortestDistances(lastStartState/1, existsTransition/2)(start, state, result) + + /** + * Gets the minimum number of transitions it takes to reach `state` from the start state. + */ + private int lengthFromStart(State state) { result = prefixLength(_, state) } + + /** + * Gets a string for which the regular expression will reach `state`. + * + * Has at most one result for any given `state`. + * This predicate will not always have a result even if there is a ReDoS issue in + * the regular expression. + */ + string prefix(State state) { + lastStartState(state) and + result = "" + or + // the search stops past the last redos candidate state. + lengthFromStart(state) <= max(lengthFromStart(any(State s | isReDoSCandidate(s, _)))) and + exists(State prev | + // select a unique predecessor (by an arbitrary measure) + prev = + min(State s, Location loc | + lengthFromStart(s) = lengthFromStart(state) - 1 and + loc = s.getRepr().getLocation() and + delta(s, _, state) + | + s + order by + loc.getStartLine(), loc.getStartColumn(), loc.getEndLine(), loc.getEndColumn(), + s.getRepr().toString() + ) + | + // greedy search for the shortest prefix + result = prefix(prev) and delta(prev, Epsilon(), state) + or + not delta(prev, Epsilon(), state) and + result = prefix(prev) + getCanonicalEdgeChar(prev, state) + ) + } + + /** + * Gets a canonical char for which there exists a transition from `prev` to `next` in the NFA. + */ + private string getCanonicalEdgeChar(State prev, State next) { + result = + min(string c | delta(prev, any(InputSymbol symbol | c = intersect(Any(), symbol)), next)) + } + + /** + * A state within a regular expression that has a pumpable state. + */ + class StateInPumpableRegexp extends State { + pragma[noinline] + StateInPumpableRegexp() { + exists(State s | isReDoSCandidate(s, _) | getRoot(s.getRepr()) = getRoot(this.getRepr())) + } + } +} + +/** + * Predicates for testing the presence of a rejecting suffix. + * + * These predicates are used to ensure that the all states reached from the fork + * by repeating `w` have a rejecting suffix. + * + * For example, a regexp like `/^(a+)+/` will accept any string as long the prefix is + * some number of `"a"`s, and it is therefore not possible to construct a rejecting suffix. + * + * A regexp like `/(a+)+$/` or `/(a+)+b/` trivially has a rejecting suffix, + * as the suffix "X" will cause both the regular expressions to be rejected. + * + * The string `w` is repeated any number of times because it needs to be + * infinitely repeatedable for the attack to work. + * For the regular expression `/((ab)+)*abab/` the accepting state is not reachable from the fork + * using epsilon transitions. But any attempt at repeating `w` will end in a state that accepts all suffixes. + */ +private module SuffixConstruction { + import PrefixConstruction + + /** + * Holds if all states reachable from `fork` by repeating `w` + * are likely rejectable by appending some suffix. + */ + predicate reachesOnlyRejectableSuffixes(State fork, string w) { + isReDoSCandidate(fork, w) and + forex(State next | next = process(fork, w, w.length() - 1) | isLikelyRejectable(next)) + } + + /** + * Holds if there likely exists a suffix starting from `s` that leads to the regular expression being rejected. + * This predicate might find impossible suffixes when searching for suffixes of length > 1, which can cause FPs. + */ + pragma[noinline] + private predicate isLikelyRejectable(StateInPumpableRegexp s) { + // exists a reject edge with some char. + hasRejectEdge(s) + or + hasEdgeToLikelyRejectable(s) + or + // stopping here is rejection + isRejectState(s) + } + + /** + * Holds if `s` is not an accept state, and there is no epsilon transition to an accept state. + */ + predicate isRejectState(StateInPumpableRegexp s) { not epsilonSucc*(s) = Accept(_) } + + /** + * Holds if there is likely a non-empty suffix leading to rejection starting in `s`. + */ + pragma[noopt] + predicate hasEdgeToLikelyRejectable(StateInPumpableRegexp s) { + // all edges (at least one) with some char leads to another state that is rejectable. + // the `next` states might not share a common suffix, which can cause FPs. + exists(string char | char = hasEdgeToLikelyRejectableHelper(s) | + // noopt to force `hasEdgeToLikelyRejectableHelper` to be first in the join-order. + exists(State next | deltaClosedChar(s, char, next) | isLikelyRejectable(next)) and + forall(State next | deltaClosedChar(s, char, next) | isLikelyRejectable(next)) + ) + } + + /** + * Gets a char for there exists a transition away from `s`, + * and `s` has not been found to be rejectable by `hasRejectEdge` or `isRejectState`. + */ + pragma[noinline] + private string hasEdgeToLikelyRejectableHelper(StateInPumpableRegexp s) { + not hasRejectEdge(s) and + not isRejectState(s) and + deltaClosedChar(s, result, _) + } + + /** + * Holds if there is a state `next` that can be reached from `prev` + * along epsilon edges, such that there is a transition from + * `prev` to `next` that the character symbol `char`. + */ + predicate deltaClosedChar(StateInPumpableRegexp prev, string char, StateInPumpableRegexp next) { + deltaClosed(prev, getAnInputSymbolMatchingRelevant(char), next) + } + + pragma[noinline] + InputSymbol getAnInputSymbolMatchingRelevant(string char) { + char = relevant(_) and + result = getAnInputSymbolMatching(char) + } + + /** + * Gets a char used for finding possible suffixes inside `root`. + */ + pragma[noinline] + private string relevant(RegExpRoot root) { + exists(ascii(result)) + or + exists(InputSymbol s | belongsTo(s, root) | result = intersect(s, _)) + or + // The characters from `hasSimpleRejectEdge`. Only `\n` is really needed (as `\n` is not in the `ascii` relation). + // The three chars must be kept in sync with `hasSimpleRejectEdge`. + result = ["|", "\n", "Z"] + } + + /** + * Holds if there exists a `char` such that there is no edge from `s` labeled `char` in our NFA. + * The NFA does not model reject states, so the above is the same as saying there is a reject edge. + */ + private predicate hasRejectEdge(State s) { + hasSimpleRejectEdge(s) + or + not hasSimpleRejectEdge(s) and + exists(string char | char = relevant(getRoot(s.getRepr())) | not deltaClosedChar(s, char, _)) + } + + /** + * Holds if there is no edge from `s` labeled with "|", "\n", or "Z" in our NFA. + * This predicate is used as a cheap pre-processing to speed up `hasRejectEdge`. + */ + private predicate hasSimpleRejectEdge(State s) { + // The three chars were chosen arbitrarily. The three chars must be kept in sync with `relevant`. + exists(string char | char = ["|", "\n", "Z"] | not deltaClosedChar(s, char, _)) + } + + /** + * Gets a state that can be reached from pumpable `fork` consuming all + * chars in `w` any number of times followed by the first `i+1` characters of `w`. + */ + pragma[noopt] + private State process(State fork, string w, int i) { + exists(State prev | prev = getProcessPrevious(fork, i, w) | + exists(string char, InputSymbol sym | + char = w.charAt(i) and + deltaClosed(prev, sym, result) and + // noopt to prevent joining `prev` with all possible `chars` that could transition away from `prev`. + // Instead only join with the set of `chars` where a relevant `InputSymbol` has already been found. + sym = getAProcessInputSymbol(char) + ) + ) + } + + /** + * Gets a state that can be reached from pumpable `fork` consuming all + * chars in `w` any number of times followed by the first `i` characters of `w`. + */ + private State getProcessPrevious(State fork, int i, string w) { + isReDoSCandidate(fork, w) and + ( + i = 0 and result = fork + or + result = process(fork, w, i - 1) + or + // repeat until fixpoint + i = 0 and + result = process(fork, w, w.length() - 1) + ) + } + + /** + * Gets an InputSymbol that matches `char`. + * The predicate is specialized to only have a result for the `char`s that are relevant for the `process` predicate. + */ + private InputSymbol getAProcessInputSymbol(string char) { + char = getAProcessChar() and + result = getAnInputSymbolMatching(char) + } + + /** + * Gets a `char` that occurs in a `pump` string. + */ + private string getAProcessChar() { result = any(string s | isReDoSCandidate(_, s)).charAt(_) } +} + +/** + * Gets the result of backslash-escaping newlines, carriage-returns and + * backslashes in `s`. + */ +bindingset[s] +private string escape(string s) { + result = + s.replaceAll("\\", "\\\\") + .replaceAll("\n", "\\n") + .replaceAll("\r", "\\r") + .replaceAll("\t", "\\t") +} + +/** + * Gets `str` with the last `i` characters moved to the front. + * + * We use this to adjust the pump string to match with the beginning of + * a RegExpTerm, so it doesn't start in the middle of a constant. + */ +bindingset[str, i] +private string rotate(string str, int i) { + result = str.suffix(str.length() - i) + str.prefix(str.length() - i) +} + +/** + * Holds if `term` may cause superlinear backtracking on strings containing many repetitions of `pump`. + * Gets the shortest string that causes superlinear backtracking. + */ +private predicate isReDoSAttackable(RegExpTerm term, string pump, State s) { + exists(int i, string c | s = Match(term, i) | + c = + min(string w | + any(ReDoSConfiguration conf).isReDoSCandidate(s, w) and + SuffixConstruction::reachesOnlyRejectableSuffixes(s, w) + | + w order by w.length(), w + ) and + pump = escape(rotate(c, i)) + ) +} + +/** + * Holds if the state `s` (represented by the term `t`) can have backtracking with repetitions of `pump`. + * + * `prefixMsg` contains a friendly message for a prefix that reaches `s` (or `prefixMsg` is the empty string if the prefix is empty or if no prefix could be found). + */ +predicate hasReDoSResult(RegExpTerm t, string pump, State s, string prefixMsg) { + isReDoSAttackable(t, pump, s) and + ( + prefixMsg = "starting with '" + escape(PrefixConstruction::prefix(s)) + "' and " and + not PrefixConstruction::prefix(s) = "" + or + PrefixConstruction::prefix(s) = "" and prefixMsg = "" + or + not exists(PrefixConstruction::prefix(s)) and prefixMsg = "" + ) +} diff --git a/java/ql/lib/semmle/code/java/security/performance/RegExpTreeView.qll b/java/ql/lib/semmle/code/java/security/performance/RegExpTreeView.qll new file mode 100644 index 00000000000..ac220ec8a50 --- /dev/null +++ b/java/ql/lib/semmle/code/java/security/performance/RegExpTreeView.qll @@ -0,0 +1,49 @@ +/** + * This module should provide a class hierarchy corresponding to a parse tree of regular expressions. + */ + +import java +import semmle.code.java.regex.RegexTreeView + +/** + * Holds if the regular expression should not be considered. + * + * We make the pragmatic performance optimization to ignore regular expressions in files + * that does not belong to the project code (such as installed dependencies). + */ +predicate isExcluded(RegExpParent parent) { + not exists(parent.getRegex().getLocation().getFile().getRelativePath()) + or + // Regexes with many occurrences of ".*" may cause the polynomial ReDoS computation to explode, so + // we explicitly exclude these. + count(int i | exists(parent.getRegex().getText().regexpFind("\\.\\*", i, _)) | i) > 10 +} + +/** + * A module containing predicates for determining which flags a regular expression have. + */ +module RegExpFlags { + /** + * Holds if `root` has the `i` flag for case-insensitive matching. + */ + predicate isIgnoreCase(RegExpTerm root) { + root.isRootTerm() and + root.getLiteral().isIgnoreCase() + } + + /** + * Gets the flags for `root`, or the empty string if `root` has no flags. + */ + string getFlags(RegExpTerm root) { + root.isRootTerm() and + result = root.getLiteral().getFlags() + } + + /** + * Holds if `root` has the `s` flag for multi-line matching. + */ + predicate isDotAll(RegExpTerm root) { + root.isRootTerm() and + root.getLiteral().isDotAll() + } +} diff --git a/java/ql/lib/semmle/code/java/security/performance/SuperlinearBackTracking.qll b/java/ql/lib/semmle/code/java/security/performance/SuperlinearBackTracking.qll new file mode 100644 index 00000000000..2b42165ff7e --- /dev/null +++ b/java/ql/lib/semmle/code/java/security/performance/SuperlinearBackTracking.qll @@ -0,0 +1,420 @@ +/** + * Provides classes for working with regular expressions that can + * perform backtracking in superlinear time. + */ + +import ReDoSUtil + +/* + * This module implements the analysis described in the paper: + * Valentin Wustholz, Oswaldo Olivo, Marijn J. H. Heule, and Isil Dillig: + * Static Detection of DoS Vulnerabilities in + * Programs that use Regular Expressions + * (Extended Version). + * (https://arxiv.org/pdf/1701.04045.pdf) + * + * Theorem 3 from the paper describes the basic idea. + * + * The following explains the idea using variables and predicate names that are used in the implementation: + * We consider a pair of repetitions, which we will call `pivot` and `succ`. + * + * We create a product automaton of 3-tuples of states (see `StateTuple`). + * There exists a transition `(a,b,c) -> (d,e,f)` in the product automaton + * iff there exists three transitions in the NFA `a->d, b->e, c->f` where those three + * transitions all match a shared character `char`. (see `getAThreewayIntersect`) + * + * We start a search in the product automaton at `(pivot, pivot, succ)`, + * and search for a series of transitions (a `Trace`), such that we end + * at `(pivot, succ, succ)` (see `isReachableFromStartTuple`). + * + * For example, consider the regular expression `/^\d*5\w*$/`. + * The search will start at the tuple `(\d*, \d*, \w*)` and search + * for a path to `(\d*, \w*, \w*)`. + * This path exists, and consists of a single transition in the product automaton, + * where the three corresponding NFA edges all match the character `"5"`. + * + * The start-state in the NFA has an any-transition to itself, this allows us to + * flag regular expressions such as `/a*$/` - which does not have a start anchor - + * and can thus start matching anywhere. + * + * The implementation is not perfect. + * It has the same suffix detection issue as the `js/redos` query, which can cause false positives. + * It also doesn't find all transitions in the product automaton, which can cause false negatives. + */ + +/** + * An instantiaion of `ReDoSConfiguration` for superlinear ReDoS. + */ +class SuperLinearReDoSConfiguration extends ReDoSConfiguration { + SuperLinearReDoSConfiguration() { this = "SuperLinearReDoSConfiguration" } + + override predicate isReDoSCandidate(State state, string pump) { isPumpable(_, state, pump) } +} + +/** + * Gets any root (start) state of a regular expression. + */ +private State getRootState() { result = mkMatch(any(RegExpRoot r)) } + +private newtype TStateTuple = + MkStateTuple(State q1, State q2, State q3) { + // starts at (pivot, pivot, succ) + isStartLoops(q1, q3) and q1 = q2 + or + step(_, _, _, _, q1, q2, q3) and FeasibleTuple::isFeasibleTuple(q1, q2, q3) + } + +/** + * A state in the product automaton. + * The product automaton contains 3-tuples of states. + * + * We lazily only construct those states that we are actually + * going to need. + * Either a start state `(pivot, pivot, succ)`, or a state + * where there exists a transition from an already existing state. + * + * The exponential variant of this query (`js/redos`) uses an optimization + * trick where `q1 <= q2`. This trick cannot be used here as the order + * of the elements matter. + */ +class StateTuple extends TStateTuple { + State q1; + State q2; + State q3; + + StateTuple() { this = MkStateTuple(q1, q2, q3) } + + /** + * Gest a string repesentation of this tuple. + */ + string toString() { result = "(" + q1 + ", " + q2 + ", " + q3 + ")" } + + /** + * Holds if this tuple is `(r1, r2, r3)`. + */ + pragma[noinline] + predicate isTuple(State r1, State r2, State r3) { r1 = q1 and r2 = q2 and r3 = q3 } +} + +/** + * A module for determining feasible tuples for the product automaton. + * + * The implementation is split into many predicates for performance reasons. + */ +private module FeasibleTuple { + /** + * Holds if the tuple `(r1, r2, r3)` might be on path from a start-state to an end-state in the product automaton. + */ + pragma[inline] + predicate isFeasibleTuple(State r1, State r2, State r3) { + // The first element is either inside a repetition (or the start state itself) + isRepetitionOrStart(r1) and + // The last element is inside a repetition + stateInsideRepetition(r3) and + // The states are reachable in the NFA in the order r1 -> r2 -> r3 + delta+(r1) = r2 and + delta+(r2) = r3 and + // The first element can reach a beginning (the "pivot" state in a `(pivot, succ)` pair). + canReachABeginning(r1) and + // The last element can reach a target (the "succ" state in a `(pivot, succ)` pair). + canReachATarget(r3) + } + + /** + * Holds if `s` is either inside a repetition, or is the start state (which is a repetition). + */ + pragma[noinline] + private predicate isRepetitionOrStart(State s) { stateInsideRepetition(s) or s = getRootState() } + + /** + * Holds if state `s` might be inside a backtracking repetition. + */ + pragma[noinline] + private predicate stateInsideRepetition(State s) { + s.getRepr().getParent*() instanceof InfiniteRepetitionQuantifier + } + + /** + * Holds if there exists a path in the NFA from `s` to a "pivot" state + * (from a `(pivot, succ)` pair that starts the search). + */ + pragma[noinline] + private predicate canReachABeginning(State s) { + delta+(s) = any(State pivot | isStartLoops(pivot, _)) + } + + /** + * Holds if there exists a path in the NFA from `s` to a "succ" state + * (from a `(pivot, succ)` pair that starts the search). + */ + pragma[noinline] + private predicate canReachATarget(State s) { delta+(s) = any(State succ | isStartLoops(_, succ)) } +} + +/** + * Holds if `pivot` and `succ` are a pair of loops that could be the beginning of a quadratic blowup. + * + * There is a slight implementation difference compared to the paper: this predicate requires that `pivot != succ`. + * The case where `pivot = succ` causes exponential backtracking and is handled by the `js/redos` query. + */ +predicate isStartLoops(State pivot, State succ) { + pivot != succ and + succ.getRepr() instanceof InfiniteRepetitionQuantifier and + delta+(pivot) = succ and + ( + pivot.getRepr() instanceof InfiniteRepetitionQuantifier + or + pivot = mkMatch(any(RegExpRoot root)) + ) +} + +/** + * Gets a state for which there exists a transition in the NFA from `s'. + */ +State delta(State s) { delta(s, _, result) } + +/** + * Holds if there are transitions from the components of `q` to the corresponding + * components of `r` labelled with `s1`, `s2`, and `s3`, respectively. + */ +pragma[noinline] +predicate step(StateTuple q, InputSymbol s1, InputSymbol s2, InputSymbol s3, StateTuple r) { + exists(State r1, State r2, State r3 | + step(q, s1, s2, s3, r1, r2, r3) and r = MkStateTuple(r1, r2, r3) + ) +} + +/** + * Holds if there are transitions from the components of `q` to `r1`, `r2`, and `r3 + * labelled with `s1`, `s2`, and `s3`, respectively. + */ +pragma[noopt] +predicate step( + StateTuple q, InputSymbol s1, InputSymbol s2, InputSymbol s3, State r1, State r2, State r3 +) { + exists(State q1, State q2, State q3 | q.isTuple(q1, q2, q3) | + deltaClosed(q1, s1, r1) and + deltaClosed(q2, s2, r2) and + deltaClosed(q3, s3, r3) and + // use noopt to force the join on `getAThreewayIntersect` to happen last. + exists(getAThreewayIntersect(s1, s2, s3)) + ) +} + +/** + * Gets a char that is matched by all the edges `s1`, `s2`, and `s3`. + * + * The result is not complete, and might miss some combination of edges that share some character. + */ +pragma[noinline] +string getAThreewayIntersect(InputSymbol s1, InputSymbol s2, InputSymbol s3) { + result = minAndMaxIntersect(s1, s2) and result = [intersect(s2, s3), intersect(s1, s3)] + or + result = minAndMaxIntersect(s1, s3) and result = [intersect(s2, s3), intersect(s1, s2)] + or + result = minAndMaxIntersect(s2, s3) and result = [intersect(s1, s2), intersect(s1, s3)] +} + +/** + * Gets the minimum and maximum characters that intersect between `a` and `b`. + * This predicate is used to limit the size of `getAThreewayIntersect`. + */ +pragma[noinline] +string minAndMaxIntersect(InputSymbol a, InputSymbol b) { + result = [min(intersect(a, b)), max(intersect(a, b))] +} + +private newtype TTrace = + Nil() or + Step(InputSymbol s1, InputSymbol s2, InputSymbol s3, TTrace t) { + exists(StateTuple p | + isReachableFromStartTuple(_, _, p, t, _) and + step(p, s1, s2, s3, _) + ) + or + exists(State pivot, State succ | isStartLoops(pivot, succ) | + t = Nil() and step(MkStateTuple(pivot, pivot, succ), s1, s2, s3, _) + ) + } + +/** + * A list of tuples of input symbols that describe a path in the product automaton + * starting from some start state. + */ +class Trace extends TTrace { + /** + * Gets a string representation of this Trace that can be used for debug purposes. + */ + string toString() { + this = Nil() and result = "Nil()" + or + exists(InputSymbol s1, InputSymbol s2, InputSymbol s3, Trace t | this = Step(s1, s2, s3, t) | + result = "Step(" + s1 + ", " + s2 + ", " + s3 + ", " + t + ")" + ) + } +} + +/** + * Gets a string corresponding to the trace `t`. + */ +string concretise(Trace t) { + t = Nil() and result = "" + or + exists(InputSymbol s1, InputSymbol s2, InputSymbol s3, Trace rest | t = Step(s1, s2, s3, rest) | + result = concretise(rest) + getAThreewayIntersect(s1, s2, s3) + ) +} + +/** + * Holds if there exists a transition from `r` to `q` in the product automaton. + * Notice that the arguments are flipped, and thus the direction is backwards. + */ +pragma[noinline] +predicate tupleDeltaBackwards(StateTuple q, StateTuple r) { step(r, _, _, _, q) } + +/** + * Holds if `tuple` is an end state in our search. + * That means there exists a pair of loops `(pivot, succ)` such that `tuple = (pivot, succ, succ)`. + */ +predicate isEndTuple(StateTuple tuple) { tuple = getAnEndTuple(_, _) } + +/** + * Gets the minimum length of a path from `r` to some an end state `end`. + * + * The implementation searches backwards from the end-tuple. + * This approach was chosen because it is way more efficient if the first predicate given to `shortestDistances` is small. + * The `end` argument must always be an end state. + */ +int distBackFromEnd(StateTuple r, StateTuple end) = + shortestDistances(isEndTuple/1, tupleDeltaBackwards/2)(end, r, result) + +/** + * Holds if there exists a pair of repetitions `(pivot, succ)` in the regular expression such that: + * `tuple` is reachable from `(pivot, pivot, succ)` in the product automaton, + * and there is a distance of `dist` from `tuple` to the nearest end-tuple `(pivot, succ, succ)`, + * and a path from a start-state to `tuple` follows the transitions in `trace`. + */ +predicate isReachableFromStartTuple(State pivot, State succ, StateTuple tuple, Trace trace, int dist) { + // base case. The first step is inlined to start the search after all possible 1-steps, and not just the ones with the shortest path. + exists(InputSymbol s1, InputSymbol s2, InputSymbol s3, State q1, State q2, State q3 | + isStartLoops(pivot, succ) and + step(MkStateTuple(pivot, pivot, succ), s1, s2, s3, tuple) and + tuple = MkStateTuple(q1, q2, q3) and + trace = Step(s1, s2, s3, Nil()) and + dist = distBackFromEnd(tuple, MkStateTuple(pivot, succ, succ)) + ) + or + // recursive case + exists(StateTuple p, Trace v, InputSymbol s1, InputSymbol s2, InputSymbol s3 | + isReachableFromStartTuple(pivot, succ, p, v, dist + 1) and + dist = isReachableFromStartTupleHelper(pivot, succ, tuple, p, s1, s2, s3) and + trace = Step(s1, s2, s3, v) + ) +} + +/** + * Helper predicate for the recursive case in `isReachableFromStartTuple`. + */ +pragma[noinline] +private int isReachableFromStartTupleHelper( + State pivot, State succ, StateTuple r, StateTuple p, InputSymbol s1, InputSymbol s2, + InputSymbol s3 +) { + result = distBackFromEnd(r, MkStateTuple(pivot, succ, succ)) and + step(p, s1, s2, s3, r) +} + +/** + * Gets the tuple `(pivot, succ, succ)` from the product automaton. + */ +StateTuple getAnEndTuple(State pivot, State succ) { + isStartLoops(pivot, succ) and + result = MkStateTuple(pivot, succ, succ) +} + +/** + * Holds if matching repetitions of `pump` can: + * 1) Transition from `pivot` back to `pivot`. + * 2) Transition from `pivot` to `succ`. + * 3) Transition from `succ` to `succ`. + * + * From theorem 3 in the paper linked in the top of this file we can therefore conclude that + * the regular expression has polynomial backtracking - if a rejecting suffix exists. + * + * This predicate is used by `SuperLinearReDoSConfiguration`, and the final results are + * available in the `hasReDoSResult` predicate. + */ +predicate isPumpable(State pivot, State succ, string pump) { + exists(StateTuple q, Trace t | + isReachableFromStartTuple(pivot, succ, q, t, _) and + q = getAnEndTuple(pivot, succ) and + pump = concretise(t) + ) +} + +/** + * Holds if repetitions of `pump` at `t` will cause polynomial backtracking. + */ +predicate polynimalReDoS(RegExpTerm t, string pump, string prefixMsg, RegExpTerm prev) { + exists(State s, State pivot | + hasReDoSResult(t, pump, s, prefixMsg) and + isPumpable(pivot, s, _) and + prev = pivot.getRepr() + ) +} + +/** + * Gets a message for why `term` can cause polynomial backtracking. + */ +string getReasonString(RegExpTerm term, string pump, string prefixMsg, RegExpTerm prev) { + polynimalReDoS(term, pump, prefixMsg, prev) and + result = + "Strings " + prefixMsg + "with many repetitions of '" + pump + + "' can start matching anywhere after the start of the preceeding " + prev +} + +/** + * A term that may cause a regular expression engine to perform a + * polynomial number of match attempts, relative to the input length. + */ +class PolynomialBackTrackingTerm extends InfiniteRepetitionQuantifier { + string reason; + string pump; + string prefixMsg; + RegExpTerm prev; + + PolynomialBackTrackingTerm() { + reason = getReasonString(this, pump, prefixMsg, prev) and + // there might be many reasons for this term to have polynomial backtracking - we pick the shortest one. + reason = min(string msg | msg = getReasonString(this, _, _, _) | msg order by msg.length(), msg) + } + + /** + * Holds if all non-empty successors to the polynomial backtracking term matches the end of the line. + */ + predicate isAtEndLine() { + forall(RegExpTerm succ | this.getSuccessor+() = succ and not matchesEpsilon(succ) | + succ instanceof RegExpDollar + ) + } + + /** + * Gets the string that should be repeated to cause this regular expression to perform polynomially. + */ + string getPumpString() { result = pump } + + /** + * Gets a message for which prefix a matching string must start with for this term to cause polynomial backtracking. + */ + string getPrefixMessage() { result = prefixMsg } + + /** + * Gets a predecessor to `this`, which also loops on the pump string, and thereby causes polynomial backtracking. + */ + RegExpTerm getPreviousLoop() { result = prev } + + /** + * Gets the reason for the number of match attempts. + */ + string getReason() { result = reason } +}