res_http_websocket: Fix crash due to double freeing memory when receiving a payload length of zero.

Frames with a payload length of 0 were incorrectly handled in res_http_websocket.
Provided a frame with a payload had been received prior it was possible for a double
free to occur. The realloc operation would succeed (thus freeing the payload) but be
treated as an error. When the session was then torn down the payload would be
freed again causing a crash. The read function now takes this into account.

This change also fixes assumptions made by users of res_http_websocket. There is no
guarantee that a frame received from it will be NULL terminated.

ASTERISK-24472 #close
Reported by: Badalian Vyacheslav

Review: https://reviewboard.asterisk.org/r/4220/
Review: https://reviewboard.asterisk.org/r/4219/


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/11@429270 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_sip.c

@@ -2596,12 +2596,16 @@ static void sip_websocket_callback(struct ast_websocket *session, struct ast_var
 		if (opcode == AST_WEBSOCKET_OPCODE_TEXT || opcode == AST_WEBSOCKET_OPCODE_BINARY) {
 			struct sip_request req = { 0, };
+			char data[payload_len + 1];
 			if (!(req.data = ast_str_create(payload_len + 1))) {
 				goto end;
 			}
-			if (ast_str_set(&req.data, -1, "%s", payload) == AST_DYNSTR_BUILD_FAILED) {
+			strncpy(data, payload, payload_len);
+			data[payload_len] = '\0';
+
+			if (ast_str_set(&req.data, -1, "%s", data) == AST_DYNSTR_BUILD_FAILED) {
 				deinit_req(&req);
 				goto end;
 			}

res/res_http_websocket.c

@@ -462,14 +462,6 @@ int AST_OPTIONAL_API_NAME(ast_websocket_read)(struct ast_websocket *session, cha
 			}
 		}
 
-		if (!(new_payload = ast_realloc(session->payload, (session->payload_len + *payload_len)))) {
-			ast_log(LOG_WARNING, "Failed allocation: %p, %zu, %"PRIu64"\n",
-				session->payload, session->payload_len, *payload_len);
-			*payload_len = 0;
-			ast_websocket_close(session, 1009);
-			return 0;
-		}
-
 		/* Per the RFC for PING we need to send back an opcode with the application data as received */
 		if ((*opcode == AST_WEBSOCKET_OPCODE_PING) && (ast_websocket_write(session, AST_WEBSOCKET_OPCODE_PONG, *payload, *payload_len))) {
 			*payload_len = 0;
@@ -477,9 +469,22 @@ int AST_OPTIONAL_API_NAME(ast_websocket_read)(struct ast_websocket *session, cha
 			return 0;
 		}
 
-		session->payload = new_payload;
-		memcpy((session->payload + session->payload_len), (*payload), (*payload_len));
-		session->payload_len += *payload_len;
+		if (*payload_len) {
+			if (!(new_payload = ast_realloc(session->payload, (session->payload_len + *payload_len)))) {
+				ast_log(LOG_WARNING, "Failed allocation: %p, %zu, %"PRIu64"\n",
+					session->payload, session->payload_len, *payload_len);
+				*payload_len = 0;
+				ast_websocket_close(session, 1009);
+				return 0;
+			}
+
+			session->payload = new_payload;
+			memcpy((session->payload + session->payload_len), (*payload), (*payload_len));
+			session->payload_len += *payload_len;
+		} else if (!session->payload_len && session->payload) {
+			ast_free(session->payload);
+			session->payload = NULL;
+		}
 
 		if (!fin && session->reconstruct && (session->payload_len < session->reconstruct)) {
 			/* If this is not a final message we need to defer returning it until later */