Explain the weird copy dance in EVP_DigestSignFinal()

with jsing

1 files changed, 3 insertions, 2 deletions

diff --git a/src/lib/libcrypto/evp/m_sigver.c b/src/lib/libcrypto/evp/m_sigver.c
index 090134c40c..d427e05db0 100644
--- a/src/lib/libcrypto/evp/m_sigver.c
+++ b/src/lib/libcrypto/evp/m_sigver.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: m_sigver.c,v 1.25 2024/03/27 06:53:15 tb Exp $ */
+/* $OpenBSD: m_sigver.c,v 1.26 2024/03/27 07:36:59 tb Exp $ */
 /* Written by Dr Stephen N Henson (steve@openssl.org) for the OpenSSL
  * project 2006.
  */
@@ -191,7 +191,7 @@ EVP_DigestSignFinal(EVP_MD_CTX *ctx, unsigned char *sigret, size_t *siglen)
                 return 1;
         }
 
-
+        /* Use a copy since EVP_DigestFinal_ex() clears secrets. */
         if ((md_ctx = EVP_MD_CTX_new()) == NULL)
                 goto err;
         if (!EVP_MD_CTX_copy_ex(md_ctx, ctx))
@@ -203,6 +203,7 @@ EVP_DigestSignFinal(EVP_MD_CTX *ctx, unsigned char *sigret, size_t *siglen)
         } else {
                 if (!EVP_DigestFinal_ex(md_ctx, md, &mdlen))
                         goto err;
+                /* Use the original ctx since secrets were cleared. */
                 if (EVP_PKEY_sign(ctx->pctx, sigret, siglen, md, mdlen) <= 0)
                         goto err;
         }