Bug 1738988 - Add support for trojan source detection in mozlint r=li…

…nter-reviewers,ahal DONTBUILD

Differential Revision: https://phabricator.services.mozilla.com/D131086

docs/code-quality/lint/linters/trojan-source.rst

@@ -0,0 +1,34 @@
+Trojan Source
+=============
+
+This linter verifies if a change is using some invalid unicode.
+
+The goal of this linter is to identify some potential usage of this
+technique:
+
+https://trojansource.codes/
+
+The code is inspired by the Red Hat script published:
+
+https://access.redhat.com/security/vulnerabilities/RHSB-2021-007#diagnostic-tools
+
+Run Locally
+-----------
+
+This mozlint linter can be run using mach:
+
+.. parsed-literal::
+
+    $ mach lint --linter trojan-source <file paths>
+
+
+Configuration
+-------------
+
+This linter is enabled on most of the code base on C/C++, Python and Rust.
+
+Sources
+-------
+
+* `Configuration (YAML) <https://searchfox.org/mozilla-central/source/tools/lint/trojan-source.yml>`_
+* `Source <https://searchfox.org/mozilla-central/source/tools/lint/trojan-source/__init__.py>`_

tools/lint/test/files/trojan-source/README

@@ -0,0 +1,5 @@
+These examples are taken from trojan source:
+https://github.com/nickboucher/trojan-source
+
+The examples are published under the MIT license.
+

tools/lint/test/files/trojan-source/commenting-out.cpp

@@ -0,0 +1,9 @@
+#include <iostream>
+
+int main() {
+    bool isAdmin = false;
+    /*‮ } ⁦if (isAdmin)⁩ ⁦ begin admins only */
+        std::cout << "You are an admin.\n";
+    /* end admins only ‮ { ⁦*/
+    return 0;
+}

tools/lint/test/files/trojan-source/early-return.py

@@ -0,0 +1,9 @@
+#!/usr/bin/env python3
+bank = { 'alice': 100 }
+
+def subtract_funds(account: str, amount: int):
+    ''' Subtract funds from bank account then ⁧''' ;return
+    bank[account] -= amount
+    return
+
+subtract_funds('alice', 50)

tools/lint/test/files/trojan-source/invisible-function.rs

@@ -0,0 +1,15 @@
+fn isAdmin() {
+    return false;
+}
+
+fn is​Admin() {
+    return true;
+}
+
+fn main() {
+    if is​Admin() {
+        printf("You are an admin\n");
+    } else {
+        printf("You are NOT an admin.\n");
+    }
+}

tools/lint/test/python.ini

@@ -31,4 +31,5 @@ skip-if = os == "win" || os == "mac"  # codespell installed on Linux
 [test_pylint.py]
 skip-if = os == "win" || os == "mac"  # only installed on linux
 requirements = tools/lint/python/pylint_requirements.txt
-
+[test_trojan_source.py]
+skip-if = os == "win"  # Python, Windows and UTF...

tools/lint/test/test_trojan_source.py

@@ -0,0 +1,28 @@
+from __future__ import absolute_import, print_function
+
+import mozunit
+
+
+LINTER = "trojan-source"
+
+
+def test_lint_trojan_source(lint, paths):
+    results = lint(paths())
+    print(results)
+    assert len(results) == 3
+
+    assert "disallowed characters" in results[0].message
+    assert results[0].level == "error"
+    assert "commenting-out.cpp" in results[0].relpath
+
+    assert "disallowed characters" in results[1].message
+    assert results[1].level == "error"
+    assert "early-return.py" in results[1].relpath
+
+    assert "disallowed characters" in results[2].message
+    assert results[2].level == "error"
+    assert "invisible-function.rs" in results[2].relpath
+
+
+if __name__ == "__main__":
+    mozunit.main()

tools/lint/trojan-source.yml

@@ -0,0 +1,19 @@
+---
+trojan-source:
+    description: Trojan Source attack - CVE-2021-42572
+    include:
+        - .
+    exclude:
+        - intl/lwbrk/rulebrk.c
+        - testing/web-platform/tests/conformance-checkers/tools/ins-del-datetime.py
+    extensions:
+        - .c
+        - .cc
+        - .cpp
+        - .h
+        - .py
+        - .rs
+    support-files:
+        - 'tools/lint/trojan-source/**'
+    type: external
+    payload: trojan-source:lint

tools/lint/trojan-source/__init__.py

@@ -0,0 +1,61 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+import sys
+import unicodedata
+
+from mozlint import result
+from mozlint.pathutils import expand_exclusions
+
+# Code inspired by Red Hat
+# https://github.com/siddhesh/find-unicode-control/
+# published under the 'BSD 3-Clause' license
+# https://access.redhat.com/security/vulnerabilities/RHSB-2021-007
+
+results = []
+
+disallowed = set(
+    chr(c) for c in range(sys.maxunicode) if unicodedata.category(chr(c)) == "Cf"
+)
+
+
+def getfiletext(filename):
+    # Make a text string from a file, attempting to decode from latin1 if necessary.
+    # Other non-utf-8 locales are not supported at the moment.
+    with open(filename, "rb") as infile:
+        try:
+            return infile.read().decode("utf-8")
+        except Exception as e:
+            print("%s: %s" % (filename, e))
+            return None
+
+    return None
+
+
+def analyze_text(filename, text, disallowed):
+    line = 0
+    for t in text.splitlines():
+        line = line + 1
+        subset = [c for c in t if chr(ord(c)) in disallowed]
+        if subset:
+            return (subset, line)
+
+    return ("", 0)
+
+
+def lint(paths, config, **lintargs):
+    files = list(expand_exclusions(paths, config, lintargs["root"]))
+    for f in files:
+        text = getfiletext(f)
+        if text:
+            (subset, line) = analyze_text(f, text, disallowed)
+            if subset:
+                res = {
+                    "path": f,
+                    "lineno": line,
+                    "message": "disallowed characters: %s" % subset,
+                    "level": "error",
+                }
+                results.append(result.from_config(config, **res))
+
+    return {"results": results, "fixed": 0}