output number of exts from tls_collect_extensions()

Modify the API of tls_collect_extensions() to be able to output the number of
extensions that are known (i.e., the length of its 'res' output).  This number
can never be zero on a successful return due to the builtin extensions list,
but use a separate output variable so as to not overload the return value
semantics.

Having this value easily available will give consumers a way to avoid repeating
the calculation.
Reviewed-by: NMatt Caswell <matt@openssl.org>
Reviewed-by: NRichard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2279)

ssl/statem/extensions.c

@@ -382,10 +382,11 @@ static int extension_is_relevant(SSL *s, unsigned int extctx,
  * extensions that we know about. We ignore others.
  */
 int tls_collect_extensions(SSL *s, PACKET *packet, unsigned int context,
-                           RAW_EXTENSION **res, int *al)
+                           RAW_EXTENSION **res, int *al, size_t *len)
 {
     PACKET extensions = *packet;
     size_t i = 0;
+    size_t num_exts;
     custom_ext_methods *exts = NULL;
     RAW_EXTENSION *raw_extensions = NULL;
     const EXTENSION_DEFINITION *thisexd;
@@ -403,9 +404,8 @@ int tls_collect_extensions(SSL *s, PACKET *packet, unsigned int context,
         exts = &s->cert->cli_ext;
     }
 
-    raw_extensions = OPENSSL_zalloc((OSSL_NELEM(ext_defs)
-                                     + (exts != NULL ? exts->meths_count : 0))
-                                     * sizeof(*raw_extensions));
+    num_exts = OSSL_NELEM(ext_defs) + (exts != NULL ? exts->meths_count : 0);
+    raw_extensions = OPENSSL_zalloc(num_exts * sizeof(*raw_extensions));
     if (raw_extensions == NULL) {
         *al = SSL_AD_INTERNAL_ERROR;
         SSLerr(SSL_F_TLS_COLLECT_EXTENSIONS, ERR_R_MALLOC_FAILURE);
@@ -454,6 +454,8 @@ int tls_collect_extensions(SSL *s, PACKET *packet, unsigned int context,
     }
 
     *res = raw_extensions;
+    if (len != NULL)
+        *len = num_exts;
     return 1;
 
  err:

ssl/statem/statem_clnt.c

@@ -1254,7 +1254,7 @@ MSG_PROCESS_RETURN tls_process_server_hello(SSL *s, PACKET *pkt)
 
     context = SSL_IS_TLS13(s) ? EXT_TLS1_3_SERVER_HELLO
                               : EXT_TLS1_2_SERVER_HELLO;
-    if (!tls_collect_extensions(s, &extpkt, context, &extensions, &al))
+    if (!tls_collect_extensions(s, &extpkt, context, &extensions, &al, NULL))
         goto f_err;
 
     s->hit = 0;
@@ -1524,7 +1524,7 @@ static MSG_PROCESS_RETURN tls_process_hello_retry_request(SSL *s, PACKET *pkt)
     }
 
     if (!tls_collect_extensions(s, &extpkt, EXT_TLS1_3_HELLO_RETRY_REQUEST,
-                                &extensions, &al)
+                                &extensions, &al, NULL)
             || !tls_parse_all_extensions(s, EXT_TLS1_3_HELLO_RETRY_REQUEST,
                                          extensions, NULL, 0, &al))
         goto f_err;
@@ -1596,7 +1596,7 @@ MSG_PROCESS_RETURN tls_process_server_certificate(SSL *s, PACKET *pkt)
                 goto f_err;
             }
             if (!tls_collect_extensions(s, &extensions, EXT_TLS1_3_CERTIFICATE,
-                                        &rawexts, &al)
+                                        &rawexts, &al, NULL)
                     || !tls_parse_all_extensions(s, EXT_TLS1_3_CERTIFICATE,
                                                  rawexts, x, chainidx, &al)) {
                 OPENSSL_free(rawexts);
@@ -2399,7 +2399,7 @@ MSG_PROCESS_RETURN tls_process_new_session_ticket(SSL *s, PACKET *pkt)
         if (!PACKET_as_length_prefixed_2(pkt, &extpkt)
                 || !tls_collect_extensions(s, &extpkt,
                                            EXT_TLS1_3_NEW_SESSION_TICKET,
-                                           &exts, &al)
+                                           &exts, &al, NULL)
                 || !tls_parse_all_extensions(s, EXT_TLS1_3_NEW_SESSION_TICKET,
                                              exts, NULL, 0, &al)) {
             SSLerr(SSL_F_TLS_PROCESS_NEW_SESSION_TICKET, SSL_R_BAD_EXTENSION);
@@ -3362,7 +3362,7 @@ static MSG_PROCESS_RETURN tls_process_encrypted_extensions(SSL *s, PACKET *pkt)
     }
 
     if (!tls_collect_extensions(s, &extensions, EXT_TLS1_3_ENCRYPTED_EXTENSIONS,
-                                &rawexts, &al)
+                                &rawexts, &al, NULL)
             || !tls_parse_all_extensions(s, EXT_TLS1_3_ENCRYPTED_EXTENSIONS,
                                          rawexts, NULL, 0, &al))
         goto err;

ssl/statem/statem_locl.h

@@ -167,7 +167,7 @@ __owur int tls_construct_new_session_ticket(SSL *s, WPACKET *pkt);
 /* Extension processing */
 
 __owur int tls_collect_extensions(SSL *s, PACKET *packet, unsigned int context,
-                                  RAW_EXTENSION **res, int *al);
+                                  RAW_EXTENSION **res, int *al, size_t *len);
 __owur int tls_parse_extension(SSL *s, TLSEXT_INDEX idx, int context,
                                RAW_EXTENSION *exts,  X509 *x, size_t chainidx,
                                int *al);

ssl/statem/statem_srvr.c

@@ -1423,7 +1423,7 @@ MSG_PROCESS_RETURN tls_process_client_hello(SSL *s, PACKET *pkt)
     /* Preserve the raw extensions PACKET for later use */
     extensions = clienthello.extensions;
     if (!tls_collect_extensions(s, &extensions, EXT_CLIENT_HELLO,
-                                &clienthello.pre_proc_exts, &al)) {
+                                &clienthello.pre_proc_exts, &al, NULL)) {
         /* SSLerr already been called */
         goto f_err;
     }
@@ -3128,7 +3128,7 @@ MSG_PROCESS_RETURN tls_process_client_certificate(SSL *s, PACKET *pkt)
                 goto f_err;
             }
             if (!tls_collect_extensions(s, &extensions, EXT_TLS1_3_CERTIFICATE,
-                                        &rawexts, &al)
+                                        &rawexts, &al, NULL)
                     || !tls_parse_all_extensions(s, EXT_TLS1_3_CERTIFICATE,
                                                  rawexts, x, chainidx, &al)) {
                 OPENSSL_free(rawexts);