Don't write the tick_identity to the session

Sessions must be immutable once they can be shared with multiple threads.
We were breaking that rule by writing the ticket index into it during the
handshake. This can lead to incorrect behaviour, including failed
connections in multi-threaded environments.

Reported by David Benjamin.
Reviewed-by: NPaul Dale <paul.dale@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/8383)

(cherry picked from commit c96ce52ce293785b54a42d119c457aef739cc2ce)

ssl/ssl_locl.h

@@ -574,7 +574,6 @@ struct ssl_session_st {
         /* Session lifetime hint in seconds */
         unsigned long tick_lifetime_hint;
         uint32_t tick_age_add;
-        int tick_identity;
         /* Max number of bytes that can be sent as early data */
         uint32_t max_early_data;
         /* The ALPN protocol selected for this session */
@@ -1356,6 +1355,13 @@ struct ssl_st {
          * as this extension is optional on server side.
          */
         uint8_t max_fragment_len_mode;
+
+        /*
+         * On the client side the number of ticket identities we sent in the
+         * ClientHello. On the server side the identity of the ticket we
+         * selected.
+         */
+        int tick_identity;
     } ext;
 
     /*
@@ -2052,9 +2058,6 @@ typedef enum downgrade_en {
 #define TLSEXT_KEX_MODE_FLAG_KE                                 1
 #define TLSEXT_KEX_MODE_FLAG_KE_DHE                             2
 
-/* An invalid index into the TLSv1.3 PSK identities */
-#define TLSEXT_PSK_BAD_IDENTITY                                 -1
-
 #define SSL_USE_PSS(s) (s->s3->tmp.peer_sigalg != NULL && \
                         s->s3->tmp.peer_sigalg->sig == EVP_PKEY_RSA_PSS)
 

ssl/statem/extensions.c

@@ -989,7 +989,6 @@ static int final_server_name(SSL *s, unsigned int context, int sent)
                 ss->ext.ticklen = 0;
                 ss->ext.tick_lifetime_hint = 0;
                 ss->ext.tick_age_add = 0;
-                ss->ext.tick_identity = 0;
                 if (!ssl_generate_session_id(s, ss)) {
                     SSLfatal(s, SSL_AD_INTERNAL_ERROR, SSL_F_FINAL_SERVER_NAME,
                              ERR_R_INTERNAL_ERROR);
@@ -1646,7 +1645,6 @@ static int final_early_data(SSL *s, unsigned int context, int sent)
 
     if (s->max_early_data == 0
             || !s->hit
-            || s->session->ext.tick_identity != 0
             || s->early_data_state != SSL_EARLY_DATA_ACCEPTING
             || !s->ext.early_data_ok
             || s->hello_retry_request != SSL_HRR_NONE

ssl/statem/extensions_clnt.c

@@ -993,7 +993,7 @@ EXT_RETURN tls_construct_ctos_psk(SSL *s, WPACKET *pkt, unsigned int context,
     const EVP_MD *handmd = NULL, *mdres = NULL, *mdpsk = NULL;
     int dores = 0;
 
-    s->session->ext.tick_identity = TLSEXT_PSK_BAD_IDENTITY;
+    s->ext.tick_identity = 0;
 
     /*
      * Note: At this stage of the code we only support adding a single
@@ -1083,6 +1083,7 @@ EXT_RETURN tls_construct_ctos_psk(SSL *s, WPACKET *pkt, unsigned int context,
         agems += s->session->ext.tick_age_add;
 
         reshashsize = EVP_MD_size(mdres);
+        s->ext.tick_identity++;
         dores = 1;
     }
 
@@ -1142,6 +1143,7 @@ EXT_RETURN tls_construct_ctos_psk(SSL *s, WPACKET *pkt, unsigned int context,
                      ERR_R_INTERNAL_ERROR);
             return EXT_RETURN_FAIL;
         }
+        s->ext.tick_identity++;
     }
 
     if (!WPACKET_close(pkt)
@@ -1180,11 +1182,6 @@ EXT_RETURN tls_construct_ctos_psk(SSL *s, WPACKET *pkt, unsigned int context,
         return EXT_RETURN_FAIL;
     }
 
-    if (dores)
-        s->session->ext.tick_identity = 0;
-    if (s->psksession != NULL)
-        s->psksession->ext.tick_identity = (dores ? 1 : 0);
-
     return EXT_RETURN_SENT;
 #else
     return EXT_RETURN_NOT_SENT;
@@ -1927,8 +1924,7 @@ int tls_parse_stoc_early_data(SSL *s, PACKET *pkt, unsigned int context,
     }
 
     if (!s->ext.early_data_ok
-            || !s->hit
-            || s->session->ext.tick_identity != 0) {
+            || !s->hit) {
         /*
          * If we get here then we didn't send early data, or we didn't resume
          * using the first identity, or the SNI/ALPN is not consistent so the
@@ -1956,17 +1952,28 @@ int tls_parse_stoc_psk(SSL *s, PACKET *pkt, unsigned int context, X509 *x,
         return 0;
     }
 
-    if (s->session->ext.tick_identity == (int)identity) {
+    if (identity >= (unsigned int)s->ext.tick_identity) {
+        SSLfatal(s, SSL_AD_ILLEGAL_PARAMETER, SSL_F_TLS_PARSE_STOC_PSK,
+                 SSL_R_BAD_PSK_IDENTITY);
+        return 0;
+    }
+
+    /*
+     * Session resumption tickets are always sent before PSK tickets. If the
+     * ticket index is 0 then it must be for a session resumption ticket if we
+     * sent two tickets, or if we didn't send a PSK ticket.
+     */
+    if (identity == 0 && (s->psksession == NULL || s->ext.tick_identity == 2)) {
         s->hit = 1;
         SSL_SESSION_free(s->psksession);
         s->psksession = NULL;
         return 1;
     }
 
-    if (s->psksession == NULL
-            || s->psksession->ext.tick_identity != (int)identity) {
-        SSLfatal(s, SSL_AD_ILLEGAL_PARAMETER, SSL_F_TLS_PARSE_STOC_PSK,
-                 SSL_R_BAD_PSK_IDENTITY);
+    if (s->psksession == NULL) {
+        /* Should never happen */
+        SSLfatal(s, SSL_AD_INTERNAL_ERROR, SSL_F_TLS_PARSE_STOC_PSK,
+                 ERR_R_INTERNAL_ERROR);
         return 0;
     }
 
@@ -1985,6 +1992,9 @@ int tls_parse_stoc_psk(SSL *s, PACKET *pkt, unsigned int context, X509 *x,
     s->session = s->psksession;
     s->psksession = NULL;
     s->hit = 1;
+    /* Early data is only allowed if we used the first ticket */
+    if (identity != 0)
+        s->ext.early_data_ok = 0;
 #endif
 
     return 1;

ssl/statem/extensions_srvr.c

@@ -1274,7 +1274,7 @@ int tls_parse_ctos_psk(SSL *s, PACKET *pkt, unsigned int context, X509 *x,
         goto err;
     }
 
-    sess->ext.tick_identity = id;
+    s->ext.tick_identity = id;
 
     SSL_SESSION_free(s->session);
     s->session = sess;
@@ -1948,7 +1948,7 @@ EXT_RETURN tls_construct_stoc_psk(SSL *s, WPACKET *pkt, unsigned int context,
 
     if (!WPACKET_put_bytes_u16(pkt, TLSEXT_TYPE_psk)
             || !WPACKET_start_sub_packet_u16(pkt)
-            || !WPACKET_put_bytes_u16(pkt, s->session->ext.tick_identity)
+            || !WPACKET_put_bytes_u16(pkt, s->ext.tick_identity)
             || !WPACKET_close(pkt)) {
         SSLfatal(s, SSL_AD_INTERNAL_ERROR,
                  SSL_F_TLS_CONSTRUCT_STOC_PSK, ERR_R_INTERNAL_ERROR);

ssl/statem/statem_clnt.c

@@ -1613,10 +1613,7 @@ MSG_PROCESS_RETURN tls_process_server_hello(SSL *s, PACKET *pkt)
          * so the PAC-based session secret is always preserved. It'll be
          * overwritten if the server refuses resumption.
          */
-        if (s->session->session_id_length > 0
-                || (SSL_IS_TLS13(s)
-                    && s->session->ext.tick_identity
-                       != TLSEXT_PSK_BAD_IDENTITY)) {
+        if (s->session->session_id_length > 0) {
             tsan_counter(&s->session_ctx->stats.sess_miss);
             if (!ssl_get_new_session(s, 0)) {
                 /* SSLfatal() already called */