Merge pull request #2602 from chrisgavin/suspicious-date-format

Java: Add a query for suspicious date format patterns.

change-notes/1.24/analysis-java.md

@@ -11,6 +11,7 @@ The following changes in version 1.24 affect Java analysis in all applications.
 | **Query**                   | **Tags**  | **Purpose**                                                        |
 |-----------------------------|-----------|--------------------------------------------------------------------|
 | Failure to use HTTPS or SFTP URL in Maven artifact upload/download (`java/maven/non-https-url`) | security, external/cwe/cwe-300, external/cwe/cwe-319, external/cwe/cwe-494, external/cwe/cwe-829 | Finds use of insecure protocols during Maven dependency resolution. Results are shown on LGTM by default. |
+| Suspicious date format (`java/suspicious-date-format`) | correctness | Finds date format patterns that use placeholders that are likely to be incorrect. |
 
 ## Changes to existing queries
 

java/ql/src/Likely Bugs/Likely Typos/SuspiciousDateFormat.java

@@ -0,0 +1 @@
+System.out.println(new SimpleDateFormat("YYYY-MM-dd").format(new Date()));

java/ql/src/Likely Bugs/Likely Typos/SuspiciousDateFormat.qhelp

@@ -0,0 +1,42 @@
+<!DOCTYPE qhelp PUBLIC
+  "-//Semmle//qhelp//EN"
+  "qhelp.dtd">
+<qhelp>
+
+
+<overview>
+<p>
+  The Java <code>SimpleDateFormat</code> class provides many placeholders so that you can define
+  precisely the date format required. However, this also makes it easy to define a pattern that
+  doesn't behave exactly as you intended. The most common mistake is to use the <code>Y</code>
+  placeholder (which represents the ISO 8601 week year), rather than <code>y</code> (which
+  represents the actual year). In this case, the date reported will appear correct until the end
+  of the year, when the "week year" may differ from the actual year.
+</p>
+</overview>
+
+<recommendation>
+<p>
+  Ensure the format pattern's use of <code>Y</code> is correct, and if not replace it with <code>y</code>.
+</p>
+</recommendation>
+
+<example>
+<p>
+  The following example uses the date format <code>YYYY-MM-dd</code>.
+  On the 30th of December 2019, this code will output "2020-12-30", rather than the intended "2019-12-30".
+</p>
+<sample src="SuspiciousDateFormat.java" />
+<p>
+  The correct pattern in this case would be <code>yyyy-MM-dd</code> instead of <code>YYYY-MM-dd</code>.
+</p>
+</example>
+
+<references>
+<li>
+  Java Platform, Standard Edition 7, API Specification:
+  <a href="https://docs.oracle.com/javase/7/docs/api/java/text/SimpleDateFormat.html">SimpleDateFormat</a>.
+</li>
+</references>
+
+</qhelp>

java/ql/src/Likely Bugs/Likely Typos/SuspiciousDateFormat.ql

@@ -0,0 +1,19 @@
+/**
+ * @name Suspicious date format
+ * @description Using a data format that includes both 'M' and 'Y' is likely to give unexpected results.
+ * @kind problem
+ * @problem.severity warning
+ * @precision high
+ * @id java/suspicious-date-format
+ * @tags correctness
+ */
+
+import java
+
+from ConstructorCall c, string format
+where
+  c.getConstructedType().hasQualifiedName("java.text", "SimpleDateFormat") and
+  format = c.getArgument(0).(StringLiteral).getValue() and
+  format.matches("%Y%") and
+  format.matches("%M%")
+select c, "Date formatter is passed a suspicious pattern \"" + format + "\"."

java/ql/test/query-tests/SuspiciousDateFormat/A.java

@@ -0,0 +1,10 @@
+import java.text.SimpleDateFormat;
+import java.util.Date;
+
+public class A {
+	public static void main(String[] args) {
+		System.out.println(new SimpleDateFormat("yyyy-MM-dd").format(new Date())); // OK
+		System.out.println(new SimpleDateFormat("YYYY-ww").format(new Date())); // OK
+		System.out.println(new SimpleDateFormat("YYYY-MM-dd").format(new Date())); // BAD
+	}
+}

java/ql/test/query-tests/SuspiciousDateFormat/SuspiciousDateFormat.expected

@@ -0,0 +1 @@
+| A.java:8:22:8:55 | new SimpleDateFormat(...) | Date formatter is passed a suspicious pattern "YYYY-MM-dd". |

java/ql/test/query-tests/SuspiciousDateFormat/SuspiciousDateFormat.qlref

@@ -0,0 +1 @@
+Likely Bugs/Likely Typos/SuspiciousDateFormat.ql