mlkem_public_to_private: fix overread/information leak

After the guts of MLKEM_public_key were changed from a union to a struct,
the aligner grew the struct, leaking as many bytes of private key data as
the struct grew (on normal platforms that would be 2).

Ideally this would all be a bit more robust.

CID 621603 621604

ok jsing kenjiro

1 files changed, 3 insertions, 3 deletions

diff --git a/src/lib/libcrypto/mlkem/mlkem_internal.c b/src/lib/libcrypto/mlkem/mlkem_internal.c
index 653b2f332d..19dd22e036 100644
--- a/src/lib/libcrypto/mlkem/mlkem_internal.c
+++ b/src/lib/libcrypto/mlkem/mlkem_internal.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: mlkem_internal.c,v 1.1 2025/09/05 23:30:12 beck Exp $ */
+/* $OpenBSD: mlkem_internal.c,v 1.2 2025/09/14 16:47:37 tb Exp $ */
 /*
  * Copyright (c) 2024, Google Inc.
  * Copyright (c) 2024, 2025 Bob Beck <beck@obtuse.com>
@@ -990,12 +990,12 @@ mlkem_public_from_private(const MLKEM_private_key *private_key,
         case RANK768:
                 memcpy(out_public_key->key_768->bytes,
                     private_key->key_768->bytes,
-                    sizeof(struct MLKEM768_public_key));
+                    sizeof(out_public_key->key_768->bytes));
                 break;
         case RANK1024:
                 memcpy(out_public_key->key_1024->bytes,
                     private_key->key_1024->bytes,
-                    sizeof(struct MLKEM1024_public_key));
+                    sizeof(out_public_key->key_1024->bytes));
                 break;
         }
 }