AST-2018-009: Fix crash processing websocket HTTP Upgrade requests
The HTTP request processing in res_http_websocket allocates additional space on the stack for various headers received during an Upgrade request. An attacker could send a specially crafted request that causes this code to overflow the stack, resulting in a crash. * No longer allocate memory from the stack in a loop to parse the header values. NOTE: There is a slight API change when using the passed in strings as is. We now require the passed in strings to no longer have leading or trailing whitespace. This isn't a problem as the only callers have already done this before passing the strings to the affected function. ASTERISK-28013 #close Change-Id: Ia564825a8a95e085fd17e658cb777fe1afa8091a
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@ -751,7 +751,8 @@ static void websocket_bad_request(struct ast_tcptls_session_instance *ser)
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int AST_OPTIONAL_API_NAME(ast_websocket_uri_cb)(struct ast_tcptls_session_instance *ser, const struct ast_http_uri *urih, const char *uri, enum ast_http_method method, struct ast_variable *get_vars, struct ast_variable *headers)
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{
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struct ast_variable *v;
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char *upgrade = NULL, *key = NULL, *key1 = NULL, *key2 = NULL, *protos = NULL, *requested_protocols = NULL, *protocol = NULL;
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const char *upgrade = NULL, *key = NULL, *key1 = NULL, *key2 = NULL, *protos = NULL;
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char *requested_protocols = NULL, *protocol = NULL;
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int version = 0, flags = 1;
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struct ast_websocket_protocol *protocol_handler = NULL;
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struct ast_websocket *session;
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@ -770,16 +771,15 @@ int AST_OPTIONAL_API_NAME(ast_websocket_uri_cb)(struct ast_tcptls_session_instan
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/* Get the minimum headers required to satisfy our needs */
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for (v = headers; v; v = v->next) {
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if (!strcasecmp(v->name, "Upgrade")) {
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upgrade = ast_strip(ast_strdupa(v->value));
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upgrade = v->value;
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} else if (!strcasecmp(v->name, "Sec-WebSocket-Key")) {
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key = ast_strip(ast_strdupa(v->value));
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key = v->value;
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} else if (!strcasecmp(v->name, "Sec-WebSocket-Key1")) {
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key1 = ast_strip(ast_strdupa(v->value));
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key1 = v->value;
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} else if (!strcasecmp(v->name, "Sec-WebSocket-Key2")) {
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key2 = ast_strip(ast_strdupa(v->value));
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key2 = v->value;
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} else if (!strcasecmp(v->name, "Sec-WebSocket-Protocol")) {
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requested_protocols = ast_strip(ast_strdupa(v->value));
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protos = ast_strdupa(requested_protocols);
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protos = v->value;
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} else if (!strcasecmp(v->name, "Sec-WebSocket-Version")) {
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if (sscanf(v->value, "%30d", &version) != 1) {
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version = 0;
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@ -793,7 +793,7 @@ int AST_OPTIONAL_API_NAME(ast_websocket_uri_cb)(struct ast_tcptls_session_instan
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ast_sockaddr_stringify(&ser->remote_address));
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ast_http_error(ser, 426, "Upgrade Required", NULL);
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return 0;
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} else if (ast_strlen_zero(requested_protocols)) {
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} else if (ast_strlen_zero(protos)) {
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/* If there's only a single protocol registered, and the
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* client doesn't specify what protocol it's using, go ahead
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* and accept the connection */
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@ -814,9 +814,12 @@ int AST_OPTIONAL_API_NAME(ast_websocket_uri_cb)(struct ast_tcptls_session_instan
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return 0;
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}
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/* Iterate through the requested protocols trying to find one that we have a handler for */
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while (!protocol_handler && (protocol = strsep(&requested_protocols, ","))) {
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protocol_handler = ao2_find(server->protocols, ast_strip(protocol), OBJ_KEY);
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if (!protocol_handler && protos) {
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requested_protocols = ast_strdupa(protos);
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/* Iterate through the requested protocols trying to find one that we have a handler for */
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while (!protocol_handler && (protocol = strsep(&requested_protocols, ","))) {
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protocol_handler = ao2_find(server->protocols, ast_strip(protocol), OBJ_KEY);
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}
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}
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/* If no protocol handler exists bump this back to the requester */
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