Tolerate DTLS alerts with an incorrect version number

In the case of a protocol version alert being sent by a peer the record
version number may not be what we are expecting. In DTLS records with an
unexpected version number are silently discarded. This probably isn't
appropriate for alerts, so we tolerate a mismatch in the minor version
number.

This resolves an issue reported on openssl-users where an OpenSSL server
chose DTLS1.0 but the client was DTLS1.2 only and sent a protocol_version
alert with a 1.2 record number. This was silently ignored by the server.

Reviewed-by: Viktor Dukhovni <viktor@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5018)

(cherry picked from commit 08455bc9b0e69ed5f25c16fc30cc2db57cdca842)

diff --git a/ssl/record/ssl3_record.c b/ssl/record/ssl3_record.c
index a1890922546e30a0059f2e3c4df75b6f642de65b..6c74ea56896e30a953715fc32dde5a297a0ad8ee 100644 (file)
--- a/ssl/record/ssl3_record.c
+++ b/ssl/record/ssl3_record.c
@@ -1530,8 +1530,11 @@ int dtls1_get_record(SSL *s)
 
         n2s(p, rr->length);
 
-        /* Lets check version */
-        if (!s->first_packet) {
+        /*
+         * Lets check the version. We tolerate alerts that don't have the exact
+         * version number (e.g. because of protocol version errors)
+         */
+        if (!s->first_packet && rr->type != SSL3_RT_ALERT) {
             if (version != s->version) {
                 /* unexpected version, silently discard */
                 rr->length = 0;