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[3.13] gh-128657: fix _hashopenssl ref/data race (GH-128886) #129853

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Merged
merged 2 commits into from
Feb 8, 2025
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[3.13] gh-128657: fix _hashopenssl ref/data race (GH-128886) #129853

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610aa38
[3.13] gh-128657: fix _hashopenssl ref/data race (GH-128886)
tom-pytel Feb 8, 2025
53453d7
fix comment alignment
tom-pytel Feb 8, 2025
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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Library/2025-01-15-15-45-21.gh-issue-128657.P5LNQA.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Fix possible extra reference when using objects returned by :func:`hashlib.sha256` under :term:`free threading`.
34 changes: 26 additions & 8 deletions Modules/_hashopenssl.c
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Expand Up @@ -27,12 +27,13 @@
#include "pycore_hashtable.h"
#include "pycore_pyhash.h" // _Py_HashBytes()
#include "pycore_strhex.h" // _Py_strhex()
#include "pycore_pyatomic_ft_wrappers.h" // FT_ATOMIC_LOAD_PTR_RELAXED
#include "hashlib.h"

/* EVP is the preferred interface to hashing in OpenSSL */
#include <openssl/evp.h>
#include <openssl/hmac.h>
#include <openssl/crypto.h> // FIPS_mode()
#include <openssl/crypto.h> // FIPS_mode()
/* We use the object interface to discover what hashes OpenSSL supports. */
#include <openssl/objects.h>
#include <openssl/err.h>
Expand Down Expand Up @@ -370,6 +371,7 @@ static PY_EVP_MD*
py_digest_by_name(PyObject *module, const char *name, enum Py_hash_type py_ht)
{
PY_EVP_MD *digest = NULL;
PY_EVP_MD *other_digest = NULL;
_hashlibstate *state = get_hashlib_state(module);
py_hashentry_t *entry = (py_hashentry_t *)_Py_hashtable_get(
state->hashtable, (const void*)name
Expand All @@ -380,20 +382,36 @@ py_digest_by_name(PyObject *module, const char *name, enum Py_hash_type py_ht)
case Py_ht_evp:
case Py_ht_mac:
case Py_ht_pbkdf2:
if (entry->evp == NULL) {
entry->evp = PY_EVP_MD_fetch(entry->ossl_name, NULL);
digest = FT_ATOMIC_LOAD_PTR_RELAXED(entry->evp);
if (digest == NULL) {
digest = PY_EVP_MD_fetch(entry->ossl_name, NULL);
#ifdef Py_GIL_DISABLED
// exchange just in case another thread did same thing at same time
other_digest = _Py_atomic_exchange_ptr(&entry->evp, digest);
#else
entry->evp = digest;
#endif
}
digest = entry->evp;
break;
case Py_ht_evp_nosecurity:
if (entry->evp_nosecurity == NULL) {
entry->evp_nosecurity = PY_EVP_MD_fetch(entry->ossl_name, "-fips");
digest = FT_ATOMIC_LOAD_PTR_RELAXED(entry->evp_nosecurity);
if (digest == NULL) {
digest = PY_EVP_MD_fetch(entry->ossl_name, "-fips");
#ifdef Py_GIL_DISABLED
// exchange just in case another thread did same thing at same time
other_digest = _Py_atomic_exchange_ptr(&entry->evp_nosecurity, digest);
#else
entry->evp_nosecurity = digest;
#endif
}
digest = entry->evp_nosecurity;
break;
}
// if another thread same thing at same time make sure we got same ptr
assert(other_digest == NULL || other_digest == digest);
if (digest != NULL) {
PY_EVP_MD_up_ref(digest);
if (other_digest == NULL) {
PY_EVP_MD_up_ref(digest);
}
}
} else {
// Fall back for looking up an unindexed OpenSSL specific name.
Expand Down
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