From 7c1e452b2bcf8a9c060547b0991ff49b5aaa37a9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?B=C3=A9n=C3=A9dikt=20Tran?=
 <10796600+picnixz@users.noreply.github.com>
Date: Sat, 4 Jul 2026 11:16:52 +0200
Subject: [PATCH] gh-152851: fix a crash when copying a BLAKE-2s/2b object.

---
 .../Library/2026-07-04-11-14-06.gh-issue-152851.diYvTf.rst   | 2 ++
 Modules/blake2module.c                                       | 5 ++++-
 2 files changed, 6 insertions(+), 1 deletion(-)
 create mode 100644 Misc/NEWS.d/next/Library/2026-07-04-11-14-06.gh-issue-152851.diYvTf.rst

diff --git a/Misc/NEWS.d/next/Library/2026-07-04-11-14-06.gh-issue-152851.diYvTf.rst b/Misc/NEWS.d/next/Library/2026-07-04-11-14-06.gh-issue-152851.diYvTf.rst
new file mode 100644
index 00000000000000..aab033ebeed695
--- /dev/null
+++ b/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.
diff --git a/Modules/blake2module.c b/Modules/blake2module.c
index b71dd20925611e..ac7265bb9d6836 100644
--- a/Modules/blake2module.c
+++ b/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: