Java: add FileConstructorSanitizer and tests

java/ql/lib/semmle/code/java/security/PathSanitizer.qll

@@ -352,3 +352,25 @@ private class FileGetNameSanitizer extends PathInjectionSanitizer {
     )
   }
 }
+
+/**
+ * A sanitizer that considers the second argument to a `File` constructor safe
+ * if it is checked for `..` components (`PathTraversalGuard`) or if any internal
+ * `..` components are removed from it (`PathNormalizeSanitizer`).
+ */
+class FileConstructorSanitizer extends PathInjectionSanitizer {
+  FileConstructorSanitizer() {
+    exists(ConstructorCall constrCall, Argument arg, Expr guard |
+      constrCall.getConstructedType() instanceof TypeFile and
+      arg = constrCall.getArgument(1) and
+      (
+        guard
+            .(PathTraversalGuard)
+            .controls(arg.getBasicBlock(), guard.(PathTraversalGuard).getBranch())
+        or
+        TaintTracking::localExprTaint(guard.(PathNormalizeSanitizer), arg)
+      ) and
+      this.asExpr() = constrCall
+    )
+  }
+}

java/ql/test/query-tests/security/CWE-022/semmle/tests/TaintedPath.java

@@ -86,4 +86,38 @@ public void sendUserFileGood4(Socket sock, String user) throws IOException {
             fileLine = fileReader.readLine();
         }
     }
+
+    public void sendUserFileGood5(Socket sock, String user) throws IOException {
+        BufferedReader filenameReader =
+                new BufferedReader(new InputStreamReader(sock.getInputStream(), "UTF-8"));
+        String filename = filenameReader.readLine();
+        File f1 = new File("safe/file.txt");
+        // GOOD: ensure that the path does not contain ".." and is used as the
+        // second argument to a `File` constructor
+        if (!filename.contains("..")) {
+            File f2 = new File(f1, filename);
+            f2.exists();
+
+            // Only sanitize `f2`; `filename` is still tainted
+            BufferedReader fileReader = new BufferedReader(new FileReader(filename)); // $ hasTaintFlow
+        }
+    }
+
+    public void sendUserFileGood6(Socket sock, String user) throws IOException {
+        BufferedReader filenameReader =
+                new BufferedReader(new InputStreamReader(sock.getInputStream(), "UTF-8"));
+        String filename = filenameReader.readLine();
+        File f1 = new File("safe/file.txt");
+
+        // GOOD: ensure that the path is normalized and is then used as the
+        // second argument to a `File` constructor
+        Path normalizedFilename = Paths.get(filename).normalize().toAbsolutePath();
+        String normalizedFilenameStr = normalizedFilename.toString();
+        File f2 = new File(f1, normalizedFilenameStr);
+        f2.exists();
+
+        // Only sanitize `f2`; `filename` and `normalizedFilenameStr` are still tainted
+        BufferedReader fileReader = new BufferedReader(new FileReader(filename)); // $ hasTaintFlow
+        BufferedReader fileReader2 = new BufferedReader(new FileReader(normalizedFilenameStr)); // $ hasTaintFlow
+    }
 }