CVE-2023-1667:packet_cb: Log more verbose error if signature verification fails

Signed-off-by: Jakub Jelen <jjelen@redhat.com>
Reviewed-by: Norbert Pocs <npocs@redhat.com>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>

src/packet_cb.c

@@ -156,6 +156,9 @@ SSH_PACKET_CALLBACK(ssh_packet_newkeys){
                                   session->next_crypto->digest_len);
     SSH_SIGNATURE_FREE(sig);
     if (rc == SSH_ERROR) {
+      ssh_set_error(session,
+                    SSH_FATAL,
+                    "Failed to verify server hostkey signature");
       goto error;
     }
     SSH_LOG(SSH_LOG_PROTOCOL,"Signature verified and valid");