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C++: Data flow through reference parameters

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This commit is contained in:
Jonas Jensen
2019-10-01 09:33:30 +02:00
parent f417640da4
commit 7c319efb8b
15 changed files with 293 additions and 15 deletions
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1
change-notes/1.23/analysis-cpp.md
View File

@@ -30,6 +30,7 @@ The following changes in version 1.23 affect C/C++ analysis in all applications.
picture of the partial flow paths from a given source. The feature is
disabled by default and can be enabled for individual configurations by
overriding `int explorationLimit()`.
* The data-flow library now supports flow out of C++ reference parameters.
* The data-flow library now allows flow through the address-of operator (`&`).
* The `DataFlow::DefinitionByReferenceNode` class now considers `f(x)` to be a
definition of `x` when `x` is a variable of pointer type. It no longer

56
cpp/ql/src/semmle/code/cpp/dataflow/internal/DataFlowPrivate.qll
View File

@@ -51,7 +51,9 @@ class ArgumentNode extends Node {
DataFlowCall getCall() { this.argumentOf(result, _) }
}
private newtype TReturnKind = TNormalReturnKind()
private newtype TReturnKind =
TNormalReturnKind() or
TRefReturnKind(int i) { exists(Parameter parameter | i = parameter.getIndex()) }
/**
* A return kind. A return kind describes how a value can be returned
@@ -59,23 +61,54 @@ private newtype TReturnKind = TNormalReturnKind()
*/
class ReturnKind extends TReturnKind {
/** Gets a textual representation of this return kind. */
string toString() { result = "return" }
string toString() {
this instanceof TNormalReturnKind and
result = "return"
or
this instanceof TRefReturnKind and
result = "ref"
}
}
/** A data flow node that occurs as the result of a `ReturnStmt`. */
class ReturnNode extends ExprNode {
ReturnNode() { exists(ReturnStmt ret | this.getExpr() = ret.getExpr()) }
/** A data flow node that represents a returned value. */
abstract class ReturnNode extends Node {
/** Gets the kind of this returned value. */
abstract ReturnKind getKind();
}
/** A `ReturnNode` that occurs as the result of a `ReturnStmt`. */
private class NormalReturnNode extends ReturnNode, ExprNode {
NormalReturnNode() { exists(ReturnStmt ret | this.getExpr() = ret.getExpr()) }
/** Gets the kind of this returned value. */
ReturnKind getKind() { result = TNormalReturnKind() }
override ReturnKind getKind() { result = TNormalReturnKind() }
}
/**
* A `ReturnNode` that occurs as a result of a definition of a reference
* parameter reaching the end of a function body.
*/
private class RefReturnNode extends ReturnNode, RefParameterFinalValueNode {
/** Gets the kind of this returned value. */
override ReturnKind getKind() { result = TRefReturnKind(this.getParameter().getIndex()) }
}
/** A data flow node that represents the output of a call. */
class OutNode extends ExprNode {
OutNode() { this.getExpr() instanceof Call }
abstract class OutNode extends Node {
/** Gets the underlying call. */
abstract DataFlowCall getCall();
}
private class ExprOutNode extends OutNode, ExprNode {
ExprOutNode() { this.getExpr() instanceof Call }
/** Gets the underlying call. */
DataFlowCall getCall() { result = this.getExpr() }
override DataFlowCall getCall() { result = this.getExpr() }
}
private class RefOutNode extends OutNode, DefinitionByReferenceNode {
/** Gets the underlying call. */
override DataFlowCall getCall() { result = this.getArgument().getParent() }
}
/**
@@ -85,6 +118,11 @@ class OutNode extends ExprNode {
OutNode getAnOutNode(DataFlowCall call, ReturnKind kind) {
result = call.getNode() and
kind = TNormalReturnKind()
or
exists(int i |
result.asDefiningArgument() = call.getArgument(i) and
kind = TRefReturnKind(i)
)
}
/**

30
cpp/ql/src/semmle/code/cpp/dataflow/internal/DataFlowUtil.qll
View File

@@ -25,7 +25,8 @@ private newtype TNode =
not c.getTarget().getParameter(i).getUnderlyingType().(PointerType).getBaseType().isConst()
)
} or
TUninitializedNode(LocalVariable v) { not v.hasInitializer() }
TUninitializedNode(LocalVariable v) { not v.hasInitializer() } or
TRefParameterFinalValueNode(Parameter p) { exists(FlowVar var | var.reachesRefParameter(p)) }
/**
* A node in a data flow graph.
@@ -248,6 +249,23 @@ class UninitializedNode extends Node, TUninitializedNode {
LocalVariable getLocalVariable() { result = v }
}
/** INTERNAL: do not use. The final value of a non-const ref parameter. */
class RefParameterFinalValueNode extends Node, TRefParameterFinalValueNode {
Parameter p;
RefParameterFinalValueNode() { this = TRefParameterFinalValueNode(p) }
override Function getFunction() { result = p.getFunction() }
override Type getType() { result = p.getType() }
override string toString() { result = p.toString() }
override Location getLocation() { result = p.getLocation() }
Parameter getParameter() { result = p }
}
/**
* A node associated with an object after an operation that might have
* changed its state.
@@ -490,7 +508,7 @@ predicate simpleLocalFlowStep(Node nodeFrom, Node nodeTo) {
or
var.definedPartiallyAt(nodeFrom.asPartialDefinition())
) and
varToExprStep(var, nodeTo.asExpr())
varToNodeStep(var, nodeTo)
)
or
// Expr -> DefinitionByReferenceNode
@@ -533,9 +551,13 @@ private predicate exprToVarStep(Expr assignedExpr, FlowVar var) {
}
/**
* Holds if the expression `e` is an access of the variable `var`.
* Holds if the node `n` is an access of the variable `var`.
*/
private predicate varToExprStep(FlowVar var, Expr e) { e = var.getAnAccess() }
private predicate varToNodeStep(FlowVar var, Node n) {
n.asExpr() = var.getAnAccess()
or
var.reachesRefParameter(n.(RefParameterFinalValueNode).getParameter())
}
/**
* Holds if data flows from `fromExpr` to `toExpr` directly, in the case

32
cpp/ql/src/semmle/code/cpp/dataflow/internal/FlowVar.qll
View File

@@ -62,9 +62,20 @@ class FlowVar extends TFlowVar {
cached
abstract predicate definedByReference(Expr arg);
/**
* Holds if this `FlowVar` is a `PartialDefinition` whose defined expression
* is `e`.
*/
cached
abstract predicate definedPartiallyAt(Expr e);
/**
* Holds if this `FlowVar` is a definition of a reference parameter `p` that
* persists until the function returns.
*/
cached
abstract predicate reachesRefParameter(Parameter p);
/**
* Holds if this `FlowVar` corresponds to the initial value of `v`. The following
* is an exhaustive list of cases where this may happen.
@@ -338,6 +349,9 @@ module FlowVar_internal {
param = v
}
// `fullySupportedSsaVariable` excludes reference types
override predicate reachesRefParameter(Parameter p) { none() }
/**
* Holds if this `SsaVar` corresponds to a non-phi definition. Users of this
* library will never directly use an `SsaVar` that comes from a phi node,
@@ -387,6 +401,13 @@ module FlowVar_internal {
sbb = v.(Parameter).getFunction().getEntryPoint()
}
override predicate reachesRefParameter(Parameter p) {
parameterIsNonConstReference(p) and
p = v and
// This definition reaches the exit node of the function CFG
getAReachedBlockVarSBB(this).getANode() = p.getFunction()
}
override predicate definedByInitialValue(LocalScopeVariable lsv) {
blockVarDefinedByVariable(sbb, lsv) and
lsv = v
@@ -593,12 +614,23 @@ module FlowVar_internal {
private predicate variableLiveInSBB(SubBasicBlock sbb, Variable v) {
variableAccessInSBB(v, sbb, _)
or
// Non-const reference parameters are live at the end of the function
parameterIsNonConstReference(v) and
sbb.contains(v.(Parameter).getFunction())
or
exists(SubBasicBlock succ | succ = sbb.getASuccessor() |
variableLiveInSBB(succ, v) and
not variableNotLiveBefore(succ, v)
)
}
predicate parameterIsNonConstReference(Parameter p) {
exists(ReferenceType refType |
refType = p.getUnderlyingType() and
not refType.getBaseType().isConst()
)
}
/**
* Holds if liveness of `v` should stop propagating backwards from `sbb`.
*/

2
cpp/ql/test/library-tests/dataflow/dataflow-tests/lambdas.cpp
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@@ -43,5 +43,5 @@ void test_lambdas()
c = source();
};
e(t, u, w);
sink(w); // flow from source() [NOT DETECTED]
sink(w); // flow from source()
}

134
cpp/ql/test/library-tests/dataflow/dataflow-tests/ref.cpp Normal file
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@@ -0,0 +1,134 @@
int source();
template<typename T>
void sink(T);
extern int arbitrary;
namespace withoutFields {
template<typename T>
void assign(T &lhs, T rhs) {
lhs = rhs;
}
template<typename T>
void assignWrapper(T &lhs, T rhs) {
assign(lhs, rhs);
}
void notAssign(int &lhs, int rhs) {
lhs = rhs;
if (arbitrary) {
lhs = 1;
} else {
lhs = 2;
}
}
void sourceToParam(int &out) {
out = source();
if (arbitrary) {
out = 1;
}
}
void sourceToParamWrapper(int &out) {
if (arbitrary) {
sourceToParam(out);
} else {
out = 1;
}
}
void notSource(int &out) {
out = source();
if (arbitrary) {
out = 1;
} else {
out = 2;
}
}
void testRefs() {
int x1, x2, x3, x4;
assignWrapper(x1, source());
sink(x1); // flow [FALSE POSITIVE from uninitialized]
notAssign(x2, source());
sink(x2); // no flow [FALSE POSITIVE from uninitialized]
sourceToParamWrapper(x3);
sink(x3); // flow [FALSE POSITIVE from uninitialized]
notSource(x4);
sink(x4); // no flow [FALSE POSITIVE from uninitialized]
}
}
namespace withFields {
struct Int {
int val;
};
void assign(Int &lhs, int rhs) {
lhs.val = rhs;
}
void assignWrapper(Int &lhs, int rhs) {
assign(lhs, rhs);
}
void notAssign(Int &lhs, int rhs) {
lhs.val = rhs;
// Field flow ignores that the field is subsequently overwritten, leading
// to false flow here.
if (arbitrary) {
lhs.val = 1;
} else {
lhs.val = 2;
}
}
void sourceToParam(Int &out) {
out.val = source();
if (arbitrary) {
out.val = 1;
}
}
void sourceToParamWrapper(Int &out) {
if (arbitrary) {
sourceToParam(out);
} else {
out.val = 1;
}
}
void notSource(Int &out) {
out.val = source();
// Field flow ignores that the field is subsequently overwritten, leading
// to false flow here.
if (arbitrary) {
out.val = 1;
} else {
out.val = 2;
}
}
void testRefs() {
Int x1, x2, x3, x4;
assignWrapper(x1, source());
sink(x1.val); // flow
notAssign(x2, source());
sink(x2.val); // no flow [FALSE POSITIVE]
sourceToParamWrapper(x3);
sink(x3.val); // flow
notSource(x4);
sink(x4.val); // no flow [FALSE POSITIVE]
}
}

11
cpp/ql/test/library-tests/dataflow/dataflow-tests/test.expected
View File

@@ -11,6 +11,17 @@
| lambdas.cpp:29:3:29:6 | t | lambdas.cpp:8:10:8:15 | call to source |
| lambdas.cpp:35:8:35:8 | a | lambdas.cpp:8:10:8:15 | call to source |
| lambdas.cpp:41:8:41:8 | a | lambdas.cpp:8:10:8:15 | call to source |
| lambdas.cpp:46:7:46:7 | w | lambdas.cpp:43:7:43:12 | call to source |
| ref.cpp:56:10:56:11 | x1 | ref.cpp:53:9:53:10 | x1 |
| ref.cpp:56:10:56:11 | x1 | ref.cpp:55:23:55:28 | call to source |
| ref.cpp:59:10:59:11 | x2 | ref.cpp:53:13:53:14 | x2 |
| ref.cpp:62:10:62:11 | x3 | ref.cpp:29:11:29:16 | call to source |
| ref.cpp:62:10:62:11 | x3 | ref.cpp:53:17:53:18 | x3 |
| ref.cpp:65:10:65:11 | x4 | ref.cpp:53:21:53:22 | x4 |
| ref.cpp:123:13:123:15 | val | ref.cpp:122:23:122:28 | call to source |
| ref.cpp:126:13:126:15 | val | ref.cpp:125:19:125:24 | call to source |
| ref.cpp:129:13:129:15 | val | ref.cpp:94:15:94:20 | call to source |
| ref.cpp:132:13:132:15 | val | ref.cpp:109:15:109:20 | call to source |
| test.cpp:7:8:7:9 | t1 | test.cpp:6:12:6:17 | call to source |
| test.cpp:9:8:9:9 | t1 | test.cpp:6:12:6:17 | call to source |
| test.cpp:10:8:10:9 | t2 | test.cpp:6:12:6:17 | call to source |

7
cpp/ql/test/library-tests/dataflow/dataflow-tests/test_diff.expected
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@@ -8,6 +8,13 @@
| lambdas.cpp:8:10:8:15 | lambdas.cpp:29:3:29:6 | AST only |
| lambdas.cpp:8:10:8:15 | lambdas.cpp:35:8:35:8 | AST only |
| lambdas.cpp:8:10:8:15 | lambdas.cpp:41:8:41:8 | AST only |
| lambdas.cpp:43:7:43:12 | lambdas.cpp:46:7:46:7 | AST only |
| ref.cpp:29:11:29:16 | ref.cpp:62:10:62:11 | AST only |
| ref.cpp:55:23:55:28 | ref.cpp:56:10:56:11 | AST only |
| ref.cpp:94:15:94:20 | ref.cpp:129:13:129:15 | AST only |
| ref.cpp:109:15:109:20 | ref.cpp:132:13:132:15 | AST only |
| ref.cpp:122:23:122:28 | ref.cpp:123:13:123:15 | AST only |
| ref.cpp:125:19:125:24 | ref.cpp:126:13:126:15 | AST only |
| test.cpp:89:28:89:34 | test.cpp:92:8:92:14 | IR only |
| test.cpp:100:13:100:18 | test.cpp:103:10:103:12 | AST only |
| test.cpp:109:9:109:14 | test.cpp:110:10:110:12 | IR only |

4
cpp/ql/test/library-tests/dataflow/dataflow-tests/test_ir.expected
View File

@@ -5,6 +5,10 @@
| clang.cpp:37:10:37:11 | Load: m2 | clang.cpp:34:32:34:37 | Call: call to source |
| clang.cpp:41:18:41:19 | Load: m2 | clang.cpp:39:42:39:47 | Call: call to source |
| clang.cpp:45:17:45:18 | Load: m2 | clang.cpp:43:35:43:40 | Call: call to source |
| ref.cpp:56:10:56:11 | Load: x1 | ref.cpp:53:9:53:10 | Uninitialized: definition of x1 |
| ref.cpp:59:10:59:11 | Load: x2 | ref.cpp:53:13:53:14 | Uninitialized: definition of x2 |
| ref.cpp:62:10:62:11 | Load: x3 | ref.cpp:53:17:53:18 | Uninitialized: definition of x3 |
| ref.cpp:65:10:65:11 | Load: x4 | ref.cpp:53:21:53:22 | Uninitialized: definition of x4 |
| test.cpp:7:8:7:9 | Load: t1 | test.cpp:6:12:6:17 | Call: call to source |
| test.cpp:9:8:9:9 | Load: t1 | test.cpp:6:12:6:17 | Call: call to source |
| test.cpp:10:8:10:9 | Load: t2 | test.cpp:6:12:6:17 | Call: call to source |

16
cpp/ql/test/library-tests/dataflow/dataflow-tests/uninitialized.expected
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@@ -1,3 +1,19 @@
| ref.cpp:53:9:53:10 | x1 | ref.cpp:55:19:55:20 | x1 |
| ref.cpp:53:9:53:10 | x1 | ref.cpp:56:10:56:11 | x1 |
| ref.cpp:53:13:53:14 | x2 | ref.cpp:58:15:58:16 | x2 |
| ref.cpp:53:13:53:14 | x2 | ref.cpp:59:10:59:11 | x2 |
| ref.cpp:53:17:53:18 | x3 | ref.cpp:61:26:61:27 | x3 |
| ref.cpp:53:17:53:18 | x3 | ref.cpp:62:10:62:11 | x3 |
| ref.cpp:53:21:53:22 | x4 | ref.cpp:64:15:64:16 | x4 |
| ref.cpp:53:21:53:22 | x4 | ref.cpp:65:10:65:11 | x4 |
| ref.cpp:120:9:120:10 | x1 | ref.cpp:122:19:122:20 | x1 |
| ref.cpp:120:9:120:10 | x1 | ref.cpp:123:10:123:11 | x1 |
| ref.cpp:120:13:120:14 | x2 | ref.cpp:125:15:125:16 | x2 |
| ref.cpp:120:13:120:14 | x2 | ref.cpp:126:10:126:11 | x2 |
| ref.cpp:120:17:120:18 | x3 | ref.cpp:128:26:128:27 | x3 |
| ref.cpp:120:17:120:18 | x3 | ref.cpp:129:10:129:11 | x3 |
| ref.cpp:120:21:120:22 | x4 | ref.cpp:131:15:131:16 | x4 |
| ref.cpp:120:21:120:22 | x4 | ref.cpp:132:10:132:11 | x4 |
| test.cpp:75:7:75:8 | u1 | test.cpp:76:8:76:9 | u1 |
| test.cpp:83:7:83:8 | u2 | test.cpp:84:13:84:14 | u2 |
| test.cpp:83:7:83:8 | u2 | test.cpp:85:8:85:9 | u2 |

3
cpp/ql/test/library-tests/dataflow/fields/flow.expected
View File

@@ -125,6 +125,8 @@ edges
| aliasing.cpp:9:3:9:3 | s [post update] [m1] | aliasing.cpp:25:17:25:19 | ref arg & ... [m1] |
| aliasing.cpp:9:3:9:22 | ... = ... | aliasing.cpp:9:3:9:3 | s [post update] [m1] |
| aliasing.cpp:9:11:9:20 | call to user_input | aliasing.cpp:9:3:9:22 | ... = ... |
| aliasing.cpp:12:25:12:25 | s [m1] | aliasing.cpp:26:19:26:20 | ref arg s2 [m1] |
| aliasing.cpp:13:3:13:3 | s [post update] [m1] | aliasing.cpp:12:25:12:25 | s [m1] |
| aliasing.cpp:13:3:13:3 | s [post update] [m1] | aliasing.cpp:26:19:26:20 | ref arg s2 [m1] |
| aliasing.cpp:13:3:13:21 | ... = ... | aliasing.cpp:13:3:13:3 | s [post update] [m1] |
| aliasing.cpp:13:10:13:19 | call to user_input | aliasing.cpp:13:3:13:21 | ... = ... |
@@ -379,6 +381,7 @@ nodes
| aliasing.cpp:9:3:9:3 | s [post update] [m1] | semmle.label | s [post update] [m1] |
| aliasing.cpp:9:3:9:22 | ... = ... | semmle.label | ... = ... |
| aliasing.cpp:9:11:9:20 | call to user_input | semmle.label | call to user_input |
| aliasing.cpp:12:25:12:25 | s [m1] | semmle.label | s [m1] |
| aliasing.cpp:13:3:13:3 | s [post update] [m1] | semmle.label | s [post update] [m1] |
| aliasing.cpp:13:3:13:21 | ... = ... | semmle.label | ... = ... |
| aliasing.cpp:13:10:13:19 | call to user_input | semmle.label | call to user_input |

8
cpp/ql/test/library-tests/dataflow/taint-tests/localTaint.expected
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@@ -1,3 +1,8 @@
| file://:0:0:0:0 | p#0 | file://:0:0:0:0 | p#0 | |
| file://:0:0:0:0 | p#0 | file://:0:0:0:0 | p#0 | |
| file://:0:0:0:0 | p#0 | file://:0:0:0:0 | p#0 | |
| file://:0:0:0:0 | p#0 | file://:0:0:0:0 | p#0 | |
| file://:0:0:0:0 | p#0 | file://:0:0:0:0 | p#0 | |
| taint.cpp:4:27:4:33 | source1 | taint.cpp:6:13:6:19 | source1 | |
| taint.cpp:4:40:4:45 | clean1 | taint.cpp:5:8:5:13 | clean1 | |
| taint.cpp:4:40:4:45 | clean1 | taint.cpp:6:3:6:8 | clean1 | |
@@ -223,7 +228,10 @@
| taint.cpp:249:18:249:18 | a | taint.cpp:250:8:250:8 | a | |
| taint.cpp:249:25:249:25 | b | taint.cpp:251:8:251:8 | b | |
| taint.cpp:255:11:259:2 | [...](...){...} | taint.cpp:260:2:260:2 | e | |
| taint.cpp:255:19:255:19 | a | taint.cpp:255:19:255:19 | a | |
| taint.cpp:255:19:255:19 | a | taint.cpp:256:8:256:8 | a | |
| taint.cpp:255:27:255:27 | b | taint.cpp:255:27:255:27 | b | |
| taint.cpp:255:27:255:27 | b | taint.cpp:257:8:257:8 | b | |
| taint.cpp:258:7:258:12 | call to source | taint.cpp:255:35:255:35 | c | |
| taint.cpp:258:7:258:12 | call to source | taint.cpp:258:3:258:14 | ... = ... | |
| taint.cpp:260:10:260:10 | ref arg w | taint.cpp:261:7:261:7 | w | |

2
cpp/ql/test/library-tests/dataflow/taint-tests/taint.cpp
View File

@@ -258,5 +258,5 @@ void test_lambdas()
c = source();
};
e(t, u, w);
sink(w); // tainted [NOT DETECTED]
sink(w); // tainted
}

1
cpp/ql/test/library-tests/dataflow/taint-tests/taint.expected
View File

@@ -28,3 +28,4 @@
| taint.cpp:244:3:244:6 | t | taint.cpp:223:10:223:15 | call to source |
| taint.cpp:250:8:250:8 | a | taint.cpp:223:10:223:15 | call to source |
| taint.cpp:256:8:256:8 | a | taint.cpp:223:10:223:15 | call to source |
| taint.cpp:261:7:261:7 | w | taint.cpp:258:7:258:12 | call to source |

1
cpp/ql/test/library-tests/dataflow/taint-tests/test_diff.expected
View File

@@ -21,3 +21,4 @@
| taint.cpp:244:3:244:6 | taint.cpp:223:10:223:15 | AST only |
| taint.cpp:250:8:250:8 | taint.cpp:223:10:223:15 | AST only |
| taint.cpp:256:8:256:8 | taint.cpp:223:10:223:15 | AST only |
| taint.cpp:261:7:261:7 | taint.cpp:258:7:258:12 | AST only |