launch: add internal helper for socket paths creation

Introduce an internal helper to create paths for sockets -- will be
useful for changing later the logic for placing sockets.
Futhermore, check that the length of sockets won't overflow the buffer
for their filenames.

src/guestfs-internal.h

@@ -782,6 +782,7 @@ extern void guestfs_int_launch_send_progress (guestfs_h *g, int perdozen);
 extern char *guestfs_int_appliance_command_line (guestfs_h *g, const char *appliance_dev, int flags);
 #define APPLIANCE_COMMAND_LINE_IS_TCG 1
 const char *guestfs_int_get_cpu_model (int kvm);
+int guestfs_int_create_socketname (guestfs_h *g, const char *filename, char (*sockname)[UNIX_PATH_MAX]);
 extern void guestfs_int_register_backend (const char *name, const struct backend_ops *);
 extern int guestfs_int_set_backend (guestfs_h *g, const char *method);
 

src/launch-direct.c

@@ -295,7 +295,9 @@ launch_direct (guestfs_h *g, void *datav, const char *arg)
   /* Using virtio-serial, we need to create a local Unix domain socket
    * for qemu to connect to.
    */
-  snprintf (data->guestfsd_sock, sizeof data->guestfsd_sock, "%s/guestfsd.sock", g->tmpdir);
+  if (guestfs_int_create_socketname (g, "guestfsd.sock",
+                                     &data->guestfsd_sock) == -1)
+    goto cleanup0;
 
   daemon_accept_sock = socket (AF_UNIX, SOCK_STREAM|SOCK_CLOEXEC, 0);
   if (daemon_accept_sock == -1) {

src/launch-libvirt.c

@@ -395,8 +395,9 @@ launch_libvirt (guestfs_h *g, void *datav, const char *libvirt_uri)
   /* Using virtio-serial, we need to create a local Unix domain socket
    * for qemu to connect to.
    */
-  snprintf (data->guestfsd_path, sizeof data->guestfsd_path,
-            "%s/guestfsd.sock", g->tmpdir);
+  if (guestfs_int_create_socketname (g, "guestfsd.sock",
+                                     &data->guestfsd_path) == -1)
+    goto cleanup;
 
   set_socket_create_context (g);
 
@@ -421,8 +422,9 @@ launch_libvirt (guestfs_h *g, void *datav, const char *libvirt_uri)
   }
 
   /* For the serial console. */
-  snprintf (data->console_path, sizeof data->console_path,
-            "%s/console.sock", g->tmpdir);
+  if (guestfs_int_create_socketname (g, "console.sock",
+                                     &data->console_path) == -1)
+    goto cleanup;
 
   console_sock = socket (AF_UNIX, SOCK_STREAM|SOCK_CLOEXEC, 0);
   if (console_sock == -1) {

src/launch.c

@@ -418,6 +418,23 @@ guestfs_int_get_cpu_model (int kvm)
 #endif
 }
 
+/* Create the path for a socket with the selected filename in the
+ * tmpdir.
+ */
+int
+guestfs_int_create_socketname (guestfs_h *g, const char *filename,
+                               char (*sockpath)[UNIX_PATH_MAX])
+{
+  if (strlen (g->tmpdir) + 1 + strlen (filename) > UNIX_PATH_MAX-1) {
+    error (g, _("socket path too long: %s/%s"), g->tmpdir, filename);
+    return -1;
+  }
+
+  snprintf (*sockpath, UNIX_PATH_MAX, "%s/%s", g->tmpdir, filename);
+
+  return 0;
+}
+
 /* glibc documents, but does not actually implement, a 'getumask(3)'
  * call.  This implements a thread-safe way to get the umask.  Note
  * this is only called when g->verbose is true and after g->tmpdir