5.4-stable review patch. If anyone has any objections, please let me know.
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From: Al Viro viro@zeniv.linux.org.uk
[ Upstream commit 250cf3693060a5f803c5f1ddc082bb06b16112a9 ]
... 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.
Reviewed-by: Christian Brauner brauner@kernel.org Signed-off-by: Al Viro viro@zeniv.linux.org.uk Signed-off-by: Sasha Levin sashal@kernel.org --- fs/namespace.c | 6 +----- 1 file changed, 1 insertion(+), 5 deletions(-)
diff --git a/fs/namespace.c b/fs/namespace.c index 809ec3acb147c..a5cb608778b1e 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -572,12 +572,8 @@ int __legitimize_mnt(struct vfsmount *bastard, unsigned seq) smp_mb(); // see mntput_no_expire() and do_umount() 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;