Add an anti-replay mechanism

If the server is configured to allow early data then we check if the PSK
session presented by the client is available in the cache or not. If it
isn't then this may be a replay and we disallow it. If it is then we allow
it and remove the session from the cache. Note: the anti-replay protection
is not used for externally established PSKs.
Reviewed-by: NRich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5644)

ssl/ssl_sess.c

@@ -761,10 +761,10 @@ static int remove_session_lock(SSL_CTX *ctx, SSL_SESSION *c, int lck)
     if ((c != NULL) && (c->session_id_length != 0)) {
         if (lck)
             CRYPTO_THREAD_write_lock(ctx->lock);
-        if ((r = lh_SSL_SESSION_retrieve(ctx->sessions, c)) == c) {
+        if ((r = lh_SSL_SESSION_retrieve(ctx->sessions, c)) != NULL) {
             ret = 1;
-            r = lh_SSL_SESSION_delete(ctx->sessions, c);
-            SSL_SESSION_list_remove(ctx, c);
+            r = lh_SSL_SESSION_delete(ctx->sessions, r);
+            SSL_SESSION_list_remove(ctx, r);
         }
         c->not_resumable = 1;
 

ssl/statem/extensions_srvr.c

@@ -1134,6 +1134,14 @@ int tls_parse_ctos_psk(SSL *s, PACKET *pkt, unsigned int context, X509 *x,
             if (ret == SSL_TICKET_NO_DECRYPT)
                 continue;
 
+            /* Check for replay */
+            if (s->max_early_data > 0
+                    && !SSL_CTX_remove_session(s->session_ctx, sess)) {
+                SSL_SESSION_free(sess);
+                sess = NULL;
+                continue;
+            }
+
             ticket_age = (uint32_t)ticket_agel;
             now = (uint32_t)time(NULL);
             agesec = now - (uint32_t)sess->time;