Don't cache stateless tickets in TLSv1.3

In TLSv1.2 and below we always cache new sessions by default on the server
side in the internal cache (even when we're using session tickets). This is
in order to support resumption from a session id.

In TLSv1.3 there is no session id. It is only possible to resume using the
ticket. Therefore, in the default case,  there is no point in caching the
session in the internal store.

There is still a reason to call the external cache new session callback
because applications may be using the callbacks just to know about when
sessions are created (and not necessarily implementing a full cache). If
the application also implements the remove session callback then we are
forced to also store it in the internal cache so that we can create
timeout events. Otherwise the external cache could just fill up
indefinitely.

This mostly addresses the issue described in #5628. That issue also proposes
having an option to not create full stateless tickets when using the
internal cache. That aspect hasn't been addressed yet.

Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Ben Kaduk <kaduk@mit.edu>
(Merged from https://github.com/openssl/openssl/pull/6293)

diff --git a/ssl/ssl_lib.c b/ssl/ssl_lib.c
index c38fc58a5d232625d42ae735011da46a0a3624da..1dd355d0dadd4357480b490deb2b38496c5c0fb3 100644 (file)
--- a/ssl/ssl_lib.c
+++ b/ssl/ssl_lib.c
@@ -3365,13 +3365,33 @@ void ssl_update_cache(SSL *s, int mode)
 
     i = s->session_ctx->session_cache_mode;
     if ((i & mode) != 0
-        && (!s->hit || SSL_IS_TLS13(s))
-        && ((i & SSL_SESS_CACHE_NO_INTERNAL_STORE) != 0
-            || SSL_CTX_add_session(s->session_ctx, s->session))
-        && s->session_ctx->new_session_cb != NULL) {
-        SSL_SESSION_up_ref(s->session);
-        if (!s->session_ctx->new_session_cb(s, s->session))
-            SSL_SESSION_free(s->session);
+        && (!s->hit || SSL_IS_TLS13(s))) {
+        /*
+         * Add the session to the internal cache. In server side TLSv1.3 we
+         * normally don't do this because its a full stateless ticket with only
+         * a dummy session id so there is no reason to cache it, unless:
+         * - we are doing early_data, in which case we cache so that we can
+         *   detect replays
+         * - the application has set a remove_session_cb so needs to know about
+         *   session timeout events
+         */
+        if ((i & SSL_SESS_CACHE_NO_INTERNAL_STORE) == 0
+                && (!SSL_IS_TLS13(s)
+                    || !s->server
+                    || s->max_early_data > 0
+                    || s->session_ctx->remove_session_cb != NULL))
+            SSL_CTX_add_session(s->session_ctx, s->session);
+
+        /*
+         * Add the session to the external cache. We do this even in server side
+         * TLSv1.3 without early data because some applications just want to
+         * know about the creation of a session and aren't doing a full cache.
+         */
+        if (s->session_ctx->new_session_cb != NULL) {
+            SSL_SESSION_up_ref(s->session);
+            if (!s->session_ctx->new_session_cb(s, s->session))
+                SSL_SESSION_free(s->session);
+        }
     }
 
     /* auto flush every 255 connections */

diff --git a/test/sslapitest.c b/test/sslapitest.c
index fe355f2f4c9e3f4b2fa1b16d85c248e73fc0badc..fe1c1e6ff3a92658acde5a1283a3928ac60c05dd 100644 (file)
--- a/test/sslapitest.c
+++ b/test/sslapitest.c
@@ -1072,9 +1072,22 @@ static int execute_test_session(int maxprot, int use_int_cache,
             || !TEST_ptr(sess2 = SSL_get1_session(serverssl1)))
         goto end;
 
-    /* Should fail because it should already be in the cache */
-    if (use_int_cache && !TEST_false(SSL_CTX_add_session(sctx, sess2)))
-        goto end;
+    if (use_int_cache) {
+        if (maxprot == TLS1_3_VERSION && !use_ext_cache) {
+            /*
+             * In TLSv1.3 it should not have been added to the internal cache,
+             * except in the case where we also have an external cache (in that
+             * case it gets added to the cache in order to generate remove
+             * events after timeout).
+             */
+            if (!TEST_false(SSL_CTX_remove_session(sctx, sess2)))
+                goto end;
+        } else {
+            /* Should fail because it should already be in the cache */
+            if (!TEST_false(SSL_CTX_add_session(sctx, sess2)))
+                goto end;
+        }
+    }
 
     if (use_ext_cache) {
         SSL_SESSION *tmp = sess2;
@@ -1088,7 +1101,7 @@ static int execute_test_session(int maxprot, int use_int_cache,
          * the external cache. We take a copy first because
          * SSL_CTX_remove_session() also marks the session as non-resumable.
          */
-        if (use_int_cache) {
+        if (use_int_cache && maxprot != TLS1_3_VERSION) {
             if (!TEST_ptr(tmp = SSL_SESSION_dup(sess2))
                     || !TEST_true(SSL_CTX_remove_session(sctx, sess2)))
                 goto end;