Explain the weird copy dance in EVP_DigestSignFinal()

with jsing

diff --git a/lib/libcrypto/evp/m_sigver.c b/lib/libcrypto/evp/m_sigver.c
index 090134c..d427e05 100644 (file)
--- a/lib/libcrypto/evp/m_sigver.c
+++ b/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;
        }