conf: restrict open for lxc_mount_rootfs()

src/lxc/conf.c

@@ -1271,7 +1271,7 @@ static int lxc_mount_rootfs(struct lxc_conf *conf)
 	      rootfs->path, rootfs->mount,
 	      rootfs->options ? rootfs->options : "(null)");
 
-	rootfs->mntpt_fd = openat(-1, rootfs->mount, O_RDONLY | O_CLOEXEC | O_DIRECTORY | O_PATH);
+	rootfs->mntpt_fd = open_at(-EBADF, rootfs->mount, PROTECT_OPATH_DIRECTORY, PROTECT_LOOKUP_ABSOLUTE_XDEV, 0);
 	if (rootfs->mntpt_fd < 0)
 		return -errno;
 

src/lxc/syscall_wrappers.h

@@ -262,6 +262,7 @@ struct lxc_open_how {
 #define PROTECT_LOOKUP_ABSOLUTE (PROTECT_LOOKUP_BENEATH & ~RESOLVE_BENEATH)
 #define PROTECT_LOOKUP_ABSOLUTE_WITH_SYMLINKS (PROTECT_LOOKUP_ABSOLUTE & ~RESOLVE_NO_SYMLINKS)
 #define PROTECT_LOOKUP_ABSOLUTE_WITH_MAGICLINKS (PROTECT_LOOKUP_ABSOLUTE & ~(RESOLVE_NO_SYMLINKS | RESOLVE_NO_MAGICLINKS))
+#define PROTECT_LOOKUP_ABSOLUTE_XDEV (PROTECT_LOOKUP_ABSOLUTE & ~RESOLVE_NO_XDEV)
 
 #define PROTECT_OPATH_FILE (O_NOFOLLOW | O_PATH | O_CLOEXEC)
 #define PROTECT_OPATH_DIRECTORY (PROTECT_OPATH_FILE | O_DIRECTORY)