https://github.com/python/cpython/commit/90ac5398e49a80d3c2976621f5a8e449ec0db7d5
commit: 90ac5398e49a80d3c2976621f5a8e449ec0db7d5
branch: main
author: Bénédikt Tran <[email protected]>
committer: picnixz <[email protected]>
date: 2026-09-06T16:47:11+02:00
summary:
gh-155835: fix `digest_size` and `block_size` data races on SHA-3 objects
(#155838)
files:
A Misc/NEWS.d/next/Library/2026-08-15-13-12-09.gh-issue-155835.DsbSmy.rst
M Lib/test/test_hashlib.py
M Modules/sha3module.c
diff --git a/Lib/test/test_hashlib.py b/Lib/test/test_hashlib.py
index 253a8f455853f5..b511c160c9260f 100644
--- a/Lib/test/test_hashlib.py
+++ b/Lib/test/test_hashlib.py
@@ -18,6 +18,8 @@
import tempfile
import threading
import unittest
+from functools import partial
+from operator import attrgetter
from test import support
from test.support import _4G, bigmemtest
from test.support import hashlib_helper
@@ -52,18 +54,39 @@
def get_fips_mode():
return 0
+
+try:
+ import _md5
+except ImportError:
+ _md5 = None
+requires_md5 = unittest.skipUnless(_md5, 'requires _md5')
+
+
try:
import _blake2
except ImportError:
_blake2 = None
-
requires_blake2 = unittest.skipUnless(_blake2, 'requires _blake2')
+
+try:
+ import _sha1
+except ImportError:
+ _sha1 = None
+requires_sha1 = unittest.skipUnless(_sha1, 'requires _sha1')
+
+
+try:
+ import _sha2
+except ImportError:
+ _sha2 = None
+requires_sha2 = unittest.skipUnless(_sha2, 'requires _sha2')
+
+
try:
import _sha3
except ImportError:
_sha3 = None
-
requires_sha3 = unittest.skipUnless(_sha3, 'requires _sha3')
@@ -1418,5 +1441,70 @@ def scrypt(password=b"password", /, **kwargs):
self.assertRaises(numeric_exc_types, scrypt, dklen=MAX_DKLEN + 1)
+@threading_helper.requires_working_threading()
+class TestTSAN(unittest.TestCase):
+
+ @threading_helper.reap_threads
+ def check_attribute(self, write, read, expected, nthreads=8):
+ ready = threading.Event()
+ barrier = threading.Barrier(nthreads)
+
+ def writer():
+ barrier.wait()
+ while not ready.is_set():
+ write()
+
+ def reader():
+ barrier.wait()
+ while not ready.is_set():
+ self.assertEqual(read(), expected)
+
+ targets = [writer if i % 2 else reader for i in range(nthreads)]
+ workers = [threading.Thread(target=target) for target in targets]
+ with threading_helper.start_threads(workers, unlock=ready.set):
+ pass
+
+ def check_HACL_attribute(self, module, version, attrname):
+ blob = b"A" * 65536
+ obj = getattr(module, version)()
+ update = partial(obj.update, blob)
+ read = attrgetter(attrname)
+ self.check_attribute(update, partial(read, obj), read(obj))
+
+ @requires_md5
+ @support.subTests("attrname", ["block_size", "digest_size"])
+ def test_HACL_md5_attributes(self, attrname):
+ self.check_HACL_attribute(_md5, "md5", attrname)
+
+ @requires_sha1
+ @support.subTests("attrname", ["block_size", "digest_size"])
+ def test_HACL_sha1_attributes(self, attrname):
+ self.check_HACL_attribute(_sha1, "sha1", attrname)
+
+ @requires_sha2
+ @support.subTests("size", [224, 256, 384, 512])
+ @support.subTests("attrname", ["block_size", "digest_size"])
+ def test_HACL_sha2_attributes(self, size, attrname):
+ self.check_HACL_attribute(_sha2, f"sha{size}", attrname)
+
+ @requires_sha3
+ @support.subTests("size", [224, 256, 384, 512])
+ @support.subTests(
+ "attrname",
+ ["block_size", "digest_size", "_capacity_bits", "_rate_bits"],
+ )
+ def test_HACL_sha3_attributes(self, size, attrname):
+ self.check_HACL_attribute(_sha3, f"sha3_{size}", attrname)
+
+ @requires_sha3
+ @support.subTests("size", [128, 256])
+ @support.subTests(
+ "attrname",
+ ["block_size", "digest_size", "_capacity_bits", "_rate_bits"],
+ )
+ def test_HACL_shake_attributes(self, size, attrname):
+ self.check_HACL_attribute(_sha3, f"shake_{size}", attrname)
+
+
if __name__ == "__main__":
unittest.main()
diff --git
a/Misc/NEWS.d/next/Library/2026-08-15-13-12-09.gh-issue-155835.DsbSmy.rst
b/Misc/NEWS.d/next/Library/2026-08-15-13-12-09.gh-issue-155835.DsbSmy.rst
new file mode 100644
index 00000000000000..7c48daad1c29d8
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-08-15-13-12-09.gh-issue-155835.DsbSmy.rst
@@ -0,0 +1,3 @@
+:mod:`hashlib`: Fix data races when accessing
+:attr:`~hashlib.hash.digest_size` and :attr:`~hashlib.hash.block_size` on
+SHA-3 objects. Patch by Bénédikt Tran.
diff --git a/Modules/sha3module.c b/Modules/sha3module.c
index 3ddd0323575b70..3f694238de8654 100644
--- a/Modules/sha3module.c
+++ b/Modules/sha3module.c
@@ -67,6 +67,12 @@ sha3_get_state(PyObject *module)
typedef struct {
HASHLIB_OBJECT_HEAD
Hacl_Hash_SHA3_state_t *hash_state;
+ // HACL* update functions entirely replace the state, which can lead
+ // to races on the free-threaded build. Since the kind of hash is static,
+ // we can store its corresponding metadata once.
+ uint32_t digest_size;
+ uint32_t block_size;
+ int is_shake;
} SHA3object;
#define _SHA3object_CAST(op) ((SHA3object *)(op))
@@ -96,7 +102,7 @@ newSHA3object(PyTypeObject *type)
return NULL;
}
HASHLIB_INIT_MUTEX(newobj);
-
+ newobj->digest_size = newobj->block_size = 0;
PyObject_GC_Track(newobj);
return newobj;
}
@@ -179,6 +185,11 @@ py_sha3_new_impl(PyTypeObject *type, PyObject *data_obj,
int usedforsecurity,
goto error;
}
+ // set the metadata once we know that the state is valid
+ int is_shake = Hacl_Hash_SHA3_is_shake(self->hash_state);
+ self->digest_size = is_shake ? 0 :
Hacl_Hash_SHA3_hash_len(self->hash_state);
+ self->block_size = Hacl_Hash_SHA3_block_len(self->hash_state);
+
if (data) {
GET_BUFFER_VIEW_OR_ERROR(data, &buf, goto error);
/* Do not use self->mutex here as this is the constructor
@@ -253,6 +264,8 @@ _sha3_sha3_224_copy_impl(SHA3object *self, PyTypeObject
*cls)
Py_DECREF(newobj);
return PyErr_NoMemory();
}
+ newobj->digest_size = self->digest_size;
+ newobj->block_size = self->block_size;
return (PyObject *)newobj;
}
@@ -273,8 +286,7 @@ _sha3_sha3_224_digest_impl(SHA3object *self)
HASHLIB_ACQUIRE_LOCK(self);
(void)Hacl_Hash_SHA3_digest(self->hash_state, digest);
HASHLIB_RELEASE_LOCK(self);
- return PyBytes_FromStringAndSize((const char *)digest,
- Hacl_Hash_SHA3_hash_len(self->hash_state));
+ return PyBytes_FromStringAndSize((const char *)digest, self->digest_size);
}
@@ -292,8 +304,7 @@ _sha3_sha3_224_hexdigest_impl(SHA3object *self)
HASHLIB_ACQUIRE_LOCK(self);
(void)Hacl_Hash_SHA3_digest(self->hash_state, digest);
HASHLIB_RELEASE_LOCK(self);
- return _Py_strhex((const char *)digest,
- Hacl_Hash_SHA3_hash_len(self->hash_state));
+ return _Py_strhex((const char *)digest, self->digest_size);
}
@@ -334,8 +345,7 @@ static PyObject *
SHA3_get_block_size(PyObject *op, void *Py_UNUSED(closure))
{
SHA3object *self = _SHA3object_CAST(op);
- uint32_t rate = Hacl_Hash_SHA3_block_len(self->hash_state);
- return PyLong_FromLong(rate);
+ return PyLong_FromLong(self->block_size);
}
@@ -371,10 +381,7 @@ SHA3_get_digest_size(PyObject *op, void
*Py_UNUSED(closure))
{
// Preserving previous behavior: variable-length algorithms return 0
SHA3object *self = _SHA3object_CAST(op);
- if (Hacl_Hash_SHA3_is_shake(self->hash_state))
- return PyLong_FromLong(0);
- else
- return PyLong_FromLong(Hacl_Hash_SHA3_hash_len(self->hash_state));
+ return PyLong_FromLong(self->digest_size);
}
@@ -382,7 +389,7 @@ static PyObject *
SHA3_get_capacity_bits(PyObject *op, void *Py_UNUSED(closure))
{
SHA3object *self = _SHA3object_CAST(op);
- uint32_t rate = Hacl_Hash_SHA3_block_len(self->hash_state) * 8;
+ uint32_t rate = self->block_size * 8;
assert(rate <= 1600);
int capacity = 1600 - rate;
return PyLong_FromLong(capacity);
@@ -393,8 +400,7 @@ static PyObject *
SHA3_get_rate_bits(PyObject *op, void *Py_UNUSED(closure))
{
SHA3object *self = _SHA3object_CAST(op);
- uint32_t rate = Hacl_Hash_SHA3_block_len(self->hash_state) * 8;
- return PyLong_FromLong(rate);
+ return PyLong_FromLong(self->block_size * 8);
}
static PyObject *
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