[another catch from struct mount audit]
... or we risk stealing final mntput from sync umount - raising mnt_count
after umount(2) has verified that victim is not busy, but before it
has set MNT_SYNC_UMOUNT; in that case __legitimize_mnt() doesn't see
that it's safe to quietly undo mnt_count increment and leaves dropping
the reference to caller, where it'll be a full-blown mntput().
Check under mount_lock is needed; leaving the current one done before
taking that makes no sense - it's nowhere near common enough to bother
with.
Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
---
diff --git a/fs/namespace.c b/fs/namespace.c
index 98a5cd756e9a..eba4748388b1 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -790,12 +790,8 @@ int __legitimize_mnt(struct vfsmount *bastard, unsigned seq)
smp_mb(); // see mntput_no_expire()
if (likely(!read_seqretry(&mount_lock, seq)))
return 0;
- if (bastard->mnt_flags & MNT_SYNC_UMOUNT) {
- mnt_add_count(mnt, -1);
- return 1;
- }
lock_mount_hash();
- if (unlikely(bastard->mnt_flags & MNT_DOOMED)) {
+ if (unlikely(bastard->mnt_flags & (MNT_SYNC_UMOUNT | MNT_DOOMED))) {
mnt_add_count(mnt, -1);
unlock_mount_hash();
return 1;
