* [PATCH AUTOSEL 5.10 3/3] __legitimize_mnt(): check for MNT_SYNC_UMOUNT should be under mount_lock
[not found] <20250512180528.438177-1-sashal@kernel.org>
@ 2025-05-12 18:05 ` Sasha Levin
0 siblings, 0 replies; only message in thread
From: Sasha Levin @ 2025-05-12 18:05 UTC (permalink / raw)
To: patches, stable
Cc: Al Viro, Christian Brauner, Sasha Levin, linux-fsdevel,
linux-kernel
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 2f97112657adc..9f9d0d9ba4dc7 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()
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;
--
2.39.5
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