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gh-155843: properly initialize HMAC objects to prevent crashes after allocation failures #155845

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gh-155843: properly initialize HMAC objects to prevent crashes after allocation failures #155845

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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2026-08-15-13-54-22.gh-issue-155843.PD5Af3.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
:mod:`hmac`: ensure that HMAC objects are properly initialized to prevent
rare crashes on allocation failures. Patch by Bénédikt Tran.
33 changes: 23 additions & 10 deletions Modules/hmacmodule.c
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Original file line number Diff line number Diff line change
Expand Up @@ -676,6 +676,24 @@ has_uint32_t_buffer_length(const Py_buffer *buffer)

// --- HMAC object ------------------------------------------------------------

/*
* Create a zero-initialized untracked HMAC object.
*
* Return NULL on failure with an exception set.
*/
static HMACObject *
hmac_new_object(PyTypeObject *tp)
{
HMACObject *self = (HMACObject *)tp->tp_alloc(tp, 0);
if (self == NULL) {
return NULL;
}
HASHLIB_INIT_MUTEX(self);
// tp_alloc initialize the memory to zero but the unknown kind must be -1
self->kind = Py_hmac_kind_hash_unknown;
return self;
}

/*
* Use the HMAC information 'info' to populate the corresponding fields.
*
Expand All @@ -687,7 +705,7 @@ hmac_set_hinfo(hmacmodule_state *state,
HMACObject *self, const py_hmac_hinfo *info)
{
assert(info->display_name != NULL);
self->name = Py_NewRef(info->display_name);
Py_XSETREF(self->name, Py_NewRef(info->display_name));
assert_is_static_hmac_hash_kind(info->kind);
self->kind = narrow_hmac_hash_kind(state, info->kind);
assert(info->block_size <= Py_hmac_hash_max_block_size);
Expand Down Expand Up @@ -756,16 +774,15 @@ _hmac_new_impl(PyObject *module, PyObject *keyobj, PyObject *msgobj,
return NULL;
}

HMACObject *self = PyObject_New(HMACObject, state->hmac_type);
HMACObject *self = hmac_new_object(state->hmac_type);
if (self == NULL) {
return NULL;
}
HASHLIB_INIT_MUTEX(self);
hmac_set_hinfo(state, self, info);
int rc;
// Create the HACL* internal state with the given key.
Py_buffer key;
GET_BUFFER_VIEW_OR_ERROR(keyobj, &key, goto error_on_key);
GET_BUFFER_VIEW_OR_ERROR(keyobj, &key, goto error);
rc = hmac_new_initial_state(self, key.buf, key.len);
PyBuffer_Release(&key);
if (rc < 0) {
Expand Down Expand Up @@ -793,8 +810,6 @@ _hmac_new_impl(PyObject *module, PyObject *keyobj, PyObject *msgobj,
assert(rc == 0);
return (PyObject *)self;

error_on_key:
self->state = NULL;
error:
Py_DECREF(self);
return NULL;
Expand All @@ -807,7 +822,7 @@ static void
hmac_copy_hinfo(HMACObject *out, const HMACObject *src)
{
assert(src->name != NULL);
out->name = Py_NewRef(src->name);
Py_XSETREF(out->name, Py_NewRef(src->name));
assert(src->kind != Py_hmac_kind_hash_unknown);
out->kind = src->kind;
assert(src->block_size <= Py_hmac_hash_max_block_size);
Expand Down Expand Up @@ -850,8 +865,7 @@ static PyObject *
_hmac_HMAC_copy_impl(HMACObject *self, PyTypeObject *cls)
/*[clinic end generated code: output=a955bfa55b65b215 input=17b2c0ad0b147e36]*/
{
hmacmodule_state *state = get_hmacmodule_state_by_cls(cls);
HMACObject *copy = PyObject_New(HMACObject, state->hmac_type);
HMACObject *copy = hmac_new_object(Py_TYPE(self));
if (copy == NULL) {
return NULL;
}
Expand All @@ -868,7 +882,6 @@ _hmac_HMAC_copy_impl(HMACObject *self, PyTypeObject *cls)
return NULL;
}

HASHLIB_INIT_MUTEX(copy);
return (PyObject *)copy;
}

Expand Down
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