gh-152851: fix a crash when copying a BLAKE-2s/2b object (#153008)

Author: picnixz

Misc/NEWS.d/next/Library/2026-07-04-11-14-06.gh-issue-152851.diYvTf.rst

@@ -0,0 +1,2 @@
+Prevent a crash when allocation fails while copying a :func:`BLAKE-2s/2b
+<hashlib.blake2b>` object. Patch by Bénédikt Tran.

Modules/blake2module.c

@@ -757,6 +757,10 @@ blake2_blake2b_copy_unlocked(Blake2Object *self, Blake2Object *cpy)
         }                                                                   \
     } while (0)
 
+    // Ensure that the implementation type is consistent with the HACL* state.
+    // See https://github.com/python/cpython/issues/152851 for details.
+    cpy->impl = self->impl;
+
     switch (self->impl) {
 #if _Py_HACL_CAN_COMPILE_VEC256
         case Blake2b_256:
@@ -778,7 +782,6 @@ blake2_blake2b_copy_unlocked(Blake2Object *self, Blake2Object *cpy)
             Py_UNREACHABLE();
     }
 #undef BLAKE2_COPY
-    cpy->impl = self->impl;
     return 0;
 
 error: