Fail if an unrecognised record type is received

TLS1.0 and TLS1.1 say you SHOULD ignore unrecognised record types, but
TLS 1.2 says you MUST send an unexpected message alert. We swap to the
TLS 1.2 behaviour for all protocol versions to prevent issues where no
progress is being made and the peer continually sends unrecognised record
types, using up resources processing them.

Issue reported by 郭志攀
Reviewed-by: NTim Hudson <tjh@openssl.org>

ssl/record/rec_layer_s3.c

@@ -1463,14 +1463,12 @@ int ssl3_read_bytes(SSL *s, int type, int *recvd_type, unsigned char *buf,
     switch (SSL3_RECORD_get_type(rr)) {
     default:
         /*
-         * TLS up to v1.1 just ignores unknown message types: TLS v1.2 give
-         * an unexpected message alert.
+         * TLS 1.0 and 1.1 say you SHOULD ignore unrecognised record types, but
+         * TLS 1.2 says you MUST send an unexpected message alert. We use the
+         * TLS 1.2 behaviour for all protocol versions to prevent issues where
+         * no progress is being made and the peer continually sends unrecognised
+         * record types, using up resources processing them.
          */
-        if (s->version >= TLS1_VERSION && s->version <= TLS1_1_VERSION) {
-            SSL3_RECORD_set_length(rr, 0);
-            SSL3_RECORD_set_read(rr);
-            goto start;
-        }
         al = SSL_AD_UNEXPECTED_MESSAGE;
         SSLerr(SSL_F_SSL3_READ_BYTES, SSL_R_UNEXPECTED_RECORD);
         goto f_err;