mount: Enable "DefaultPermissions" FUSE option by default

This enforces the Unix permissions of the snapshot files within the mounted filesystem, which will only allow users to access snapshot files if they had access to the file outside of the snapshot.

cmd/restic/cmd_mount.go

@@ -120,6 +120,8 @@ func mount(opts MountOptions, gopts GlobalOptions, mountpoint string) error {
 		mountOptions = append(mountOptions, systemFuse.AllowOther())
 	}
 
+	mountOptions = append(mountOptions, systemFuse.DefaultPermissions())
+
 	c, err := systemFuse.Mount(mountpoint, mountOptions...)
 	if err != nil {
 		return err