gh-127298: When in FIPS mode ensure builtin hashes check for usedforsecurity=False

Lib/hashlib.py

@@ -79,6 +79,23 @@
     'blake2b', 'blake2s',
 }
 
+# Wrapper that only allows usage when usedforsecurity=False
+# (effectively unapproved service indicator)
+def __usedforsecurity_check(md, name, *args, **kwargs):
+    if kwargs.get("usedforsecurity", True):
+        raise ValueError(name + " is blocked when usedforsecurity=True")
+    return md(*args, **kwargs)
+
+# If the _hashlib OpenSSL wrapper is in FIPS mode, wrap other implementations
+# to check the usedforsecurity kwarg. All builtin implementations are treated
+# as only available for useforsecurity=False purposes in the presence of such
+# a configured and linked OpenSSL.
+def __get_wrapped_builtin(md, name):
+    if __openssl_fips_mode != 0:
+        from functools import partial
+        return partial(__usedforsecurity_check, md, name)
+    return md
+
 def __get_builtin_constructor(name):
     cache = __builtin_constructor_cache
     constructor = cache.get(name)
@@ -87,32 +104,32 @@ def __get_builtin_constructor(name):
     try:
         if name in {'SHA1', 'sha1'}:
             import _sha1
-            cache['SHA1'] = cache['sha1'] = _sha1.sha1
+            cache['SHA1'] = cache['sha1'] = __get_wrapped_builtin(_sha1.sha1, name)
         elif name in {'MD5', 'md5'}:
             import _md5
-            cache['MD5'] = cache['md5'] = _md5.md5
+            cache['MD5'] = cache['md5'] = __get_wrapped_builtin(_md5.md5, name)
         elif name in {'SHA256', 'sha256', 'SHA224', 'sha224'}:
             import _sha2
-            cache['SHA224'] = cache['sha224'] = _sha2.sha224
-            cache['SHA256'] = cache['sha256'] = _sha2.sha256
+            cache['SHA224'] = cache['sha224'] = __get_wrapped_builtin(_sha2.sha224, name)
+            cache['SHA256'] = cache['sha256'] = __get_wrapped_builtin(_sha2.sha256, name)
         elif name in {'SHA512', 'sha512', 'SHA384', 'sha384'}:
             import _sha2
-            cache['SHA384'] = cache['sha384'] = _sha2.sha384
-            cache['SHA512'] = cache['sha512'] = _sha2.sha512
+            cache['SHA384'] = cache['sha384'] = __get_wrapped_builtin(_sha2.sha384, name)
+            cache['SHA512'] = cache['sha512'] = __get_wrapped_builtin(_sha2.sha512, name)
         elif name in {'blake2b', 'blake2s'}:
             import _blake2
-            cache['blake2b'] = _blake2.blake2b
-            cache['blake2s'] = _blake2.blake2s
+            cache['blake2b'] = __get_wrapped_builtin(_blake2.blake2b, name)
+            cache['blake2s'] = __get_wrapped_builtin(_blake2.blake2s, name)
         elif name in {'sha3_224', 'sha3_256', 'sha3_384', 'sha3_512'}:
             import _sha3
-            cache['sha3_224'] = _sha3.sha3_224
-            cache['sha3_256'] = _sha3.sha3_256
-            cache['sha3_384'] = _sha3.sha3_384
-            cache['sha3_512'] = _sha3.sha3_512
+            cache['sha3_224'] = __get_wrapped_builtin(_sha3.sha3_224, name)
+            cache['sha3_256'] = __get_wrapped_builtin(_sha3.sha3_256, name)
+            cache['sha3_384'] = __get_wrapped_builtin(_sha3.sha3_384, name)
+            cache['sha3_512'] = __get_wrapped_builtin(_sha3.sha3_512, name)
         elif name in {'shake_128', 'shake_256'}:
             import _sha3
-            cache['shake_128'] = _sha3.shake_128
-            cache['shake_256'] = _sha3.shake_256
+            cache['shake_128'] = __get_wrapped_builtin(_sha3.shake_128, name)
+            cache['shake_256'] = __get_wrapped_builtin(_sha3.shake_256, name)
     except ImportError:
         pass  # no extension module, this hash is unsupported.
 
@@ -161,9 +178,8 @@ def __hash_new(name, data=b'', **kwargs):
     except ValueError:
         # If the _hashlib module (OpenSSL) doesn't support the named
         # hash, try using our builtin implementations.
-        # This allows for SHA224/256 and SHA384/512 support even though
-        # the OpenSSL library prior to 0.9.8 doesn't provide them.
-        return __get_builtin_constructor(name)(data)
+        # OpenSSL may not have been compiled to support everything.
+        return __get_builtin_constructor(name)(data, **kwargs)
 
 
 try:
@@ -172,10 +188,15 @@ def __hash_new(name, data=b'', **kwargs):
     __get_hash = __get_openssl_constructor
     algorithms_available = algorithms_available.union(
             _hashlib.openssl_md_meth_names)
+    try:
+        __openssl_fips_mode = _hashlib.get_fips_mode()
+    except ValueError:
+        __openssl_fips_mode = 0
 except ImportError:
     _hashlib = None
     new = __py_new
     __get_hash = __get_builtin_constructor
+    __openssl_fips_mode = 0
 
 try:
     # OpenSSL's PKCS5_PBKDF2_HMAC requires OpenSSL 1.0+ with HMAC and SHA

Lib/test/hashlibdata/openssl.cnf

@@ -0,0 +1,19 @@
+# Activate base provider only, with default properties fips=yes. It
+# means that fips mode is on, and no digest implementations are
+# available. Perfect for mock testing builtin FIPS wrappers.
+
+config_diagnostics = 1
+openssl_conf = openssl_init
+
+[openssl_init]
+providers = provider_sect
+alg_section = algorithm_sect
+
+[provider_sect]
+base = base_sect
+
+[base_sect]
+activate = 1
+
+[algorithm_sect]
+default_properties = fips=yes

Lib/test/ssltests.py

@@ -7,7 +7,7 @@
 
 TESTS = [
     'test_asyncio', 'test_ensurepip.py', 'test_ftplib', 'test_hashlib',
-    'test_hmac', 'test_httplib', 'test_imaplib',
+    'test_hashlib_fips', 'test_hmac', 'test_httplib', 'test_imaplib',
     'test_poplib', 'test_ssl', 'test_smtplib', 'test_smtpnet',
     'test_urllib2_localnet', 'test_venv', 'test_xmlrpc'
 ]

Lib/test/test_hashlib_fips.py

@@ -0,0 +1,63 @@
+# Test the hashlib module usedforsecurity wrappers under fips.
+#
+#  Copyright (C) 2024   Dimitri John Ledkov (dimitri.ledkov@surgut.co.uk)
+#  Licensed to PSF under a Contributor Agreement.
+#
+
+import os
+import sys
+import unittest
+
+OPENSSL_CONF_BACKUP = os.environ.get("OPENSSL_CONF")
+
+
+class HashLibFIPSTestCase(unittest.TestCase):
+    @classmethod
+    def setUpClass(cls):
+        if sys.modules.get("_hashlib") or sys.modules.get("_ssl"):
+            raise AssertionError("_hashlib or _ssl already imported, too late to change OPENSSL_CONF.")
+        # This openssl.cnf mocks FIPS mode without any digest
+        # loaded. It means all digests must raise ValueError when
+        # usedforsecurity=True via either openssl or builtin
+        # constructors
+        OPENSSL_CONF = os.path.join(os.path.dirname(__file__), "hashlibdata", "openssl.cnf")
+        os.environ["OPENSSL_CONF"] = OPENSSL_CONF
+        # Ensure hashlib is loading a fresh libcrypto with openssl
+        # context affected by the above config file. Check if this can
+        # be folded into test_hashlib.py, specifically if
+        # import_fresh_module() results in a fresh library context
+        import hashlib
+
+    def setUp(self):
+        try:
+            from _hashlib import get_fips_mode
+        except ImportError:
+            self.skipTest('_hashlib not available')
+
+        if get_fips_mode() != 1:
+            self.skipTest('mocking fips mode failed')
+
+    @classmethod
+    def tearDownClass(cls):
+        if OPENSSL_CONF_BACKUP is not None:
+            os.environ["OPENSSL_CONF"] = OPENSSL_CONF_BACKUP
+        else:
+            os.environ.pop("OPENSSL_CONF", None)
+
+    def test_algorithms_available(self):
+        import hashlib
+        self.assertTrue(set(hashlib.algorithms_guaranteed).
+                            issubset(hashlib.algorithms_available))
+        # all available algorithms must be loadable, bpo-47101
+        self.assertNotIn("undefined", hashlib.algorithms_available)
+        for name in hashlib.algorithms_available:
+            digest = hashlib.new(name, usedforsecurity=False)
+
+    def test_usedforsecurity_true(self):
+        import hashlib
+        for name in hashlib.algorithms_available:
+            with self.assertRaises(ValueError):
+                digest = hashlib.new(name, usedforsecurity=True)
+
+if __name__ == "__main__":
+    unittest.main()

Makefile.pre.in

@@ -2447,6 +2447,7 @@ TESTSUBDIRS=	idlelib/idle_test \
 		test/decimaltestdata \
 		test/dtracedata \
 		test/encoded_modules \
+		test/hashlibdata \
 		test/leakers \
 		test/libregrtest \
 		test/mathdata \

Misc/NEWS.d/next/Library/2024-11-26-16-31-40.gh-issue-127298.jqYJvn.rst

@@ -0,0 +1,8 @@
+:mod:`hashlib`'s builtin hash implementations now check ``usedforsecurity=False``,
+when the OpenSSL library default provider is in OpenSSL's FIPS mode.  This helps
+ensure that only US FIPS approved implementations are in use by default on systems
+configured as such.
+
+This is only active when :mod:`hashlib` has been built with OpenSSL implementation
+support and said OpenSSL library includes the FIPS mode feature.  Not all variants
+do, and OpenSSL is not a *required* build time dependency of ``hashlib``.