Add additional tests from real world query run

java/ql/src/Security/CWE/CWE-023/PartialPathTraversal.qhelp

@@ -0,0 +1,46 @@
+<!DOCTYPE qhelp PUBLIC
+  "-//Semmle//qhelp//EN"
+  "qhelp.dtd">
+<qhelp>
+<overview>
+<p>Accessing paths controlled by users can allow an attacker to access unexpected resources. This 
+can result in sensitive information being revealed or deleted, or an attacker being able to influence
+behavior by modifying unexpected files.</p>
+
+<p>Paths that are naively constructed from data controlled by a user may contain unexpected special characters,
+such as "..". Such a path may potentially point to any directory on the file system.</p>
+
+</overview>
+<recommendation>
+
+<p>Validate user input before using it to construct a file path. Ideally, follow these rules:</p>
+
+<ul>
+<li>Do not allow more than a single "." character.</li>
+<li>Do not allow directory separators such as "/" or "\" (depending on the file system).</li>
+<li>Do not rely on simply replacing problematic sequences such as "../". For example, after applying this filter to
+".../...//" the resulting string would still be "../".</li>
+<li>Ideally use a whitelist of known good patterns.</li>
+</ul>
+
+</recommendation>
+<example>
+
+<p>In this example, a file name is read from a <code>java.net.Socket</code> and then used to access a file in the
+user's home directory and send it back over the socket. However, a malicious user could enter a file name which contains special 
+characters. For example, the string "../../etc/passwd" will result in the code reading the file located at 
+"/home/[user]/../../etc/passwd", which is the system's password file. This file would then be sent back to the user, 
+giving them access to all the system's passwords.</p>
+
+<sample src="PartialPathTraversal.java" />
+
+</example>
+<references>
+
+<li>
+OWASP:
+<a href="https://owasp.org/www-community/attacks/Path_Traversal">Path Traversal</a>.
+</li>
+
+</references>
+</qhelp>

java/ql/src/Security/CWE/CWE-023/PartialPathTraversal.ql

@@ -39,14 +39,24 @@ class SystemPropFileSeparatorExpr extends FileSeparatorExpr {
 }
 
 class StringLiteralFileSeparatorExpr extends FileSeparatorExpr, StringLiteral {
-  StringLiteralFileSeparatorExpr() { this.getValue() = "/" }
+  StringLiteralFileSeparatorExpr() {
+    this.getValue().matches("%/") or this.getValue().matches("%\\")
+  }
+}
+
+class CharacterLiteralFileSeparatorExpr extends FileSeparatorExpr, CharacterLiteral {
+  CharacterLiteralFileSeparatorExpr() { this.getValue() = "/" or this.getValue() = "\\" }
 }
 
 class FileSeparatorAppend extends AddExpr {
   FileSeparatorAppend() { this.getRightOperand() instanceof FileSeparatorExpr }
 }
 
-predicate isSafe(Expr expr) { DataFlow::localExprFlow(any(FileSeparatorAppend fsa), expr) }
+predicate isSafe(Expr expr) {
+  DataFlow::localExprFlow(any(Expr e |
+      e instanceof FileSeparatorAppend or e instanceof FileSeparatorExpr
+    ), expr)
+}
 
 from MethodAccess ma
 where

java/ql/test/query-tests/security/CWE-023/semmle/tests/PartialPathTraversalTest.java

@@ -218,8 +218,22 @@ public class PartialPathTraversalTest {
         }
     }
 
+    void foo24(File dir, File parent) throws IOException {
+        String parentCanonical = parent.getCanonicalPath();
+        if (!dir.getCanonicalPath().startsWith(parentCanonical + '/')) {
+            throw new IOException("Invalid directory: " + dir.getCanonicalPath());
+        }
+    }
+
     public void doesNotFlag() {
         "hello".startsWith("goodbye");
     }
 
+    public void doesNotFlagBackslash(File file) throws IOException {
+        // https://github.com/jenkinsci/jenkins/blob/be3cf6bffe7aa2fe2307c424fa418519f3bbd73b/core/src/main/java/hudson/util/jna/Kernel32Utils.java#L77-L77
+        if (!file.getCanonicalPath().startsWith("\\\\")) {
+            throw new RuntimeException("Boom");
+        }
+    }
+
 }