Validate ClientHello session_id field length and send alert on failure

RT#4080
Reviewed-by: NRich Salz <rsalz@openssl.org>
Reviewed-by: NMatt Caswell <matt@openssl.org>

ssl/ssl_sess.c

@@ -529,12 +529,8 @@ int ssl_get_prev_session(SSL *s, const PACKET *ext, const PACKET *session_id)
     int fatal = 0;
     int try_session_cache = 1;
     int r;
-    size_t len = PACKET_remaining(session_id);
 
-    if (len > SSL_MAX_SSL_SESSION_ID_LENGTH)
-        goto err;
-
-    if (len == 0)
+    if (PACKET_remaining(session_id) == 0)
         try_session_cache = 0;
 
     /* sets s->tlsext_ticket_expected and extended master secret flag */

ssl/statem/statem_srvr.c

@@ -1082,6 +1082,12 @@ MSG_PROCESS_RETURN tls_process_client_hello(SSL *s, PACKET *pkt)
             goto f_err;
         }
 
+        if (session_id_len > SSL_MAX_SSL_SESSION_ID_LENGTH) {
+            al = SSL_AD_DECODE_ERROR;
+            SSLerr(SSL_F_TLS_PROCESS_CLIENT_HELLO, SSL_R_LENGTH_MISMATCH);
+            goto f_err;
+        }
+
         if (!PACKET_get_sub_packet(pkt, &cipher_suites, cipher_len)
             || !PACKET_get_sub_packet(pkt, &session_id, session_id_len)
             || !PACKET_get_sub_packet(pkt, &challenge, challenge_len)
@@ -1116,6 +1122,12 @@ MSG_PROCESS_RETURN tls_process_client_hello(SSL *s, PACKET *pkt)
             goto f_err;
         }
 
+        if (PACKET_remaining(&session_id) > SSL_MAX_SSL_SESSION_ID_LENGTH) {
+            al = SSL_AD_DECODE_ERROR;
+            SSLerr(SSL_F_TLS_PROCESS_CLIENT_HELLO, SSL_R_LENGTH_MISMATCH);
+            goto f_err;
+        }
+
         if (SSL_IS_DTLS(s)) {
             if (!PACKET_get_length_prefixed_1(pkt, &cookie)) {
                 al = SSL_AD_DECODE_ERROR;