Annotate misuse of EVP_Digest()

The session_id member of SSL_SESSION has 32 bytes for historical
reasons.  This precisely accommodates a SHA-256 and is currently
computed using this hash.  If the hash function is ever changed,
this will likely overflow.  This should be fixed in code.  Leave
it at an XXX comment for now.

Pointed out by jsing

diff --git a/lib/libssl/ssl_clnt.c b/lib/libssl/ssl_clnt.c
index d5791e3..9cedc08 100644 (file)
--- a/lib/libssl/ssl_clnt.c
+++ b/lib/libssl/ssl_clnt.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ssl_clnt.c,v 1.155 2022/10/02 16:36:41 jsing Exp $ */
+/* $OpenBSD: ssl_clnt.c,v 1.156 2022/10/20 15:18:54 tb Exp $ */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -1647,6 +1647,7 @@ ssl3_get_new_session_ticket(SSL *s)
         * assumptions elsewhere in OpenSSL. The session ID is set
         * to the SHA256 hash of the ticket.
         */
+       /* XXX - ensure this doesn't overflow session_id if hash is changed. */
        if (!EVP_Digest(CBS_data(&session_ticket), CBS_len(&session_ticket),
            s->session->session_id, &session_id_length, EVP_sha256(), NULL)) {
                al = SSL_AD_INTERNAL_ERROR;