Use flexible array member for 'struct trigger_service_params3'

No functional change, but the new code is shorter (and simpler).  Also
drop a pointless check that the command is NUL-terminated, as
qrexec-daemon will do that anyway.

agent/qrexec-agent.c

@@ -819,9 +819,7 @@ static void reap_children(void)
 static void handle_trigger_io(void)
 {
     struct msg_header hdr;
-    struct trigger_service_params3 params;
-    char *command = NULL;
-    size_t command_len;
+    struct trigger_service_params3 *params = NULL;
     int client_fd;
 
     client_fd = do_accept(trigger_fd);
@@ -830,40 +828,32 @@ static void handle_trigger_io(void)
     if (!read_all(client_fd, &hdr, sizeof(hdr)))
         goto error;
     if (hdr.type != MSG_TRIGGER_SERVICE3 ||
-            hdr.len <= sizeof(params) ||
-            hdr.len > sizeof(params) + MAX_SERVICE_NAME_LEN) {
+            hdr.len <= sizeof(*params) ||
+            hdr.len > sizeof(*params) + MAX_SERVICE_NAME_LEN) {
         LOG(ERROR, "Invalid request received from qrexec-client-vm, is it outdated?");
         goto error;
     }
-    if (!read_all(client_fd, &params, sizeof(params)))
+    params = malloc(hdr.len);
+    if (!params)
         goto error;
-    command_len = hdr.len - sizeof(params);
-    command = malloc(command_len);
-    if (!command)
-        goto error;
-    if (!read_all(client_fd, command, command_len))
-        goto error;
-    if (command[command_len-1] != '\0')
+    if (!read_all(client_fd, params, hdr.len))
         goto error;
 
-    int res = snprintf(params.request_id.ident, sizeof(params.request_id), "SOCKET%d", client_fd);
-    if (res < 0 || res >= (int)sizeof(params.request_id))
+    int res = snprintf(params->request_id.ident, sizeof(params->request_id), "SOCKET%d", client_fd);
+    if (res < 0 || res >= (int)sizeof(params->request_id))
         abort();
     if (libvchan_send(ctrl_vchan, &hdr, sizeof(hdr)) != sizeof(hdr))
         handle_vchan_error("write hdr");
-    if (libvchan_send(ctrl_vchan, &params, sizeof(params)) != sizeof(params))
+    if (libvchan_send(ctrl_vchan, params, hdr.len) != (int)hdr.len)
         handle_vchan_error("write params");
-    if (libvchan_send(ctrl_vchan, command, command_len) != (int)command_len)
-        handle_vchan_error("write command");
 
-    free(command);
+    free(params);
     /* do not close client_fd - we'll need it to send the connection details
      * later (when dom0 accepts the request) */
     return;
 error:
     LOG(ERROR, "Failed to retrieve/execute request from qrexec-client-vm");
-    if (command)
-        free(command);
+    free(params);
     close(client_fd);
 }
 

daemon/qrexec-daemon.c

@@ -1412,55 +1412,48 @@ void handle_message_from_agent(void)
             return;
         }
         case MSG_TRIGGER_SERVICE3: {
-            struct trigger_service_params3 untrusted_params3, params3;
-            size_t service_name_len = hdr.len - sizeof(untrusted_params3), nul_offset;
-            char *untrusted_service_name = malloc(service_name_len), *service_name = NULL;
+            struct trigger_service_params3 *untrusted_params3, *params3;
 
-            if (!untrusted_service_name)
+            untrusted_params3 = malloc(hdr.len);
+            if (!untrusted_params3)
                 handle_vchan_error("malloc(service_name)");
 
-            if (libvchan_recv(vchan, &untrusted_params3, sizeof(untrusted_params3))
-                    != sizeof(untrusted_params3)) {
-                free(untrusted_service_name);
-                handle_vchan_error("recv params3");
-            }
-            if (libvchan_recv(vchan, untrusted_service_name, service_name_len)
-                    != (int)service_name_len) {
-                free(untrusted_service_name);
+            if (libvchan_recv(vchan, untrusted_params3, hdr.len)
+                    != (int)hdr.len) {
+                free(untrusted_params3);
                 handle_vchan_error("recv params3(service_name)");
             }
-            service_name_len -= 1;
+            size_t const service_name_len = hdr.len - sizeof(*untrusted_params3) - 1;
 
             /* sanitize start */
-            ENSURE_NULL_TERMINATED(untrusted_params3.target_domain);
-            sanitize_name(untrusted_params3.target_domain, "@:");
-            if (!validate_request_id(&untrusted_params3.request_id, "MSG_TRIGGER_SERVICE3"))
+            ENSURE_NULL_TERMINATED(untrusted_params3->target_domain);
+            sanitize_name(untrusted_params3->target_domain, "@:");
+            if (!validate_request_id(&untrusted_params3->request_id, "MSG_TRIGGER_SERVICE3"))
                 goto fail3;
-            params3 = untrusted_params3;
-            if (untrusted_service_name[service_name_len] != 0) {
+            if (untrusted_params3->service_name[service_name_len] != 0) {
                 LOG(ERROR, "Service name not NUL-terminated");
                 goto fail3;
             }
-            nul_offset = strlen(untrusted_service_name);
+            size_t const nul_offset = strlen(untrusted_params3->service_name);
             if (nul_offset != service_name_len) {
                 LOG(ERROR, "Service name contains NUL byte at offset %zu", nul_offset);
                 goto fail3;
             }
-            if (!validate_service_name(untrusted_service_name))
+            if (!validate_service_name(untrusted_params3->service_name))
                 goto fail3;
-            service_name = untrusted_service_name;
-            untrusted_service_name = NULL;
+            params3 = untrusted_params3;
+            untrusted_params3 = NULL;
             /* sanitize end */
 
             handle_execute_service(remote_domain_id, remote_domain_name,
-                    params3.target_domain,
-                    service_name,
-                    &params3.request_id);
-            free(service_name);
+                    params3->target_domain,
+                    params3->service_name,
+                    &params3->request_id);
+            free(params3);
             return;
 fail3:
-            send_service_refused(vchan, &untrusted_params3.request_id);
-            free(untrusted_service_name);
+            send_service_refused(vchan, &untrusted_params3->request_id);
+            free(untrusted_params3);
             return;
         }
         case MSG_CONNECTION_TERMINATED:

libqrexec/qrexec.h

@@ -139,7 +139,7 @@ struct trigger_service_params {
 struct trigger_service_params3 {
     char target_domain[64];           /* null terminated ASCII string */
     struct service_params request_id; /* service request id */
-    // char service_name[0];          /* null terminated ASCII string, size = msg_header.len - sizeof(struct trigger_service_params3) */
+    char service_name[];              /* null terminated ASCII string, size = msg_header.len - sizeof(struct trigger_service_params3) */
 };
 
 struct peer_info {