Update DUO130 to support hashlib constructor usedforsecurity=False pa…

…ram (#42)

Support for this arrived in Python 3.9, but this rule should be fully
backwards-compatible with older versions of Python.

CHANGELOG.md

@@ -5,6 +5,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
+### Changed
+- Support `usedforsecurity=False` parameter to hashlib constructors ([#39](https://github.com/dlint-py/dlint/issues/39))
 
 ## [0.12.0] - 2021-10-27
 ### Added

dlint/linters/bad_hashlib_use.py

@@ -7,10 +7,12 @@
     unicode_literals,
 )
 
-from .helpers import bad_module_attribute_use
+from .helpers import bad_kwarg_use
 
+from .. import tree
 
-class BadHashlibUseLinter(bad_module_attribute_use.BadModuleAttributeUseLinter):
+
+class BadHashlibUseLinter(bad_kwarg_use.BadKwargUseLinter):
     """This linter looks for unsafe use of the Python "hashlib" module. Use of
     md5|sha1 is known to have hash collision weaknesses.
     """
@@ -20,10 +22,20 @@ class BadHashlibUseLinter(bad_module_attribute_use.BadModuleAttributeUseLinter):
     _error_tmpl = 'DUO130 insecure use of "hashlib" module'
 
     @property
-    def illegal_module_attributes(self):
-        return {
-            'hashlib': [
-                'md5',
-                'sha1',
-            ],
-        }
+    def kwargs(self):
+        def missing_or_true(call, kwarg_name):
+            return (
+                tree.kwarg_not_present(call, kwarg_name)
+                or tree.kwarg_true(call, kwarg_name)
+            )
+
+        bad_hash_algorithms = {"md5", "sha1"}
+
+        return [
+            {
+                "module_path": f"hashlib.{hash_algorithm}",
+                "kwarg_name": "usedforsecurity",
+                "predicate": missing_or_true,
+            }
+            for hash_algorithm in bad_hash_algorithms
+        ]

docs/linters/DUO130.md

@@ -25,6 +25,10 @@ import hashlib
 sha256_hashed = hashlib.sha256(b"data").hexdigest()
 sha512_hashed = hashlib.sha512(b"data").hexdigest()
 blake2b_hashed = hashlib.blake2b(b"data").hexdigest()
+
+# Only supported in Python 3.9 and above
+md5_hashed = hashlib.md5(b"data", usedforsecurity=False).hexdigest()
+sha1_hashed = hashlib.sha1(b"data", usedforsecurity=False).hexdigest()
 # ...
 ```
 
@@ -35,3 +39,4 @@ Some algorithms have known hash collision weaknesses.
 ## Exceptions
 
 * Compatibility with systems that can only use MD5 or SHA1 and are not under your control
+* Use cases that are related to checksumming, rather than cryptography.

tests/test_bad_hashlib_use.py

@@ -45,6 +45,56 @@ def test_bad_hashlib_usage(self):
 
         assert result == expected
 
+    def test_hashlib_used_for_security(self):
+        python_node = self.get_ast_node(
+            """
+            import hashlib
+
+            var = 'echo "TEST"'
+
+            m1 = hashlib.md5(usedforsecurity=True)
+            m2 = hashlib.sha1(usedforsecurity=True)
+            """
+        )
+
+        linter = dlint.linters.BadHashlibUseLinter()
+        linter.visit(python_node)
+
+        result = linter.get_results()
+        expected = [
+            dlint.linters.base.Flake8Result(
+                lineno=6,
+                col_offset=5,
+                message=dlint.linters.BadHashlibUseLinter._error_tmpl
+            ),
+            dlint.linters.base.Flake8Result(
+                lineno=7,
+                col_offset=5,
+                message=dlint.linters.BadHashlibUseLinter._error_tmpl
+            ),
+        ]
+
+        assert result == expected
+
+    def test_hashlib_not_used_for_security(self):
+        python_node = self.get_ast_node(
+            """
+            import hashlib
+
+            var = 'echo "TEST"'
+
+            m1 = hashlib.md5(usedforsecurity=False)
+            m2 = hashlib.sha1(usedforsecurity=False)
+            """
+        )
+
+        linter = dlint.linters.BadHashlibUseLinter()
+        linter.visit(python_node)
+
+        result = linter.get_results()
+
+        assert len(result) == 0
+
 
 if __name__ == "__main__":
     unittest.main()