mnt: Clear mnt_expire during pivot_root

When inspecting the pivot_root and the current mount expiry logic I
realized that pivot_root fails to clear like mount move does.

Add the missing line in case someone does the interesting feat of
moving an expirable submount.  This gives a strong guarantee that root
of the filesystem tree will never expire.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/fs/namespace.c b/fs/namespace.c
index f87a90b98da2..fe1c77145a78 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2967,6 +2967,8 @@ SYSCALL_DEFINE2(pivot_root, const char __user *, new_root,
         /* mount new_root on / */
         attach_mnt(new_mnt, real_mount(root_parent.mnt), root_mp);
         touch_mnt_namespace(current->nsproxy->mnt_ns);
+        /* A moved mount should not expire automatically */
+        list_del_init(&new_mnt->mnt_expire);
         unlock_mount_hash();
         chroot_fs_refs(&root, &new);
         put_mountpoint(root_mp);