linux/fs/kernfs
Christian Brauner 2d2a2d7aa9
super: make iterate_supers_type() deletion-safe
iterate_supers_type() drops sb_lock while invoking the callback and keeps
only a passive reference to the current superblock. That reference keeps
the object allocated, but does not keep its s_instances node linked.

After the iterator releases s_umount, final teardown can unlink the current
s_instances node. The iterator then advances through a reinitialized node.
With the current hlist it stops without visiting the remaining superblocks.
The unlink moved from generic_shutdown_super() to kill_super_notify(), but
the cursor lifetime has been unsafe since the helper was introduced.

The CIFS DFS lookup can consequently miss a matching superblock and return
-EINVAL.

Move removal from fs_supers to put_super(), alongside removal from
super_blocks, so a passive reference keeps both list nodes linked. Keep
the filesystem module reference until then, since unlinking s_instances
may touch type->fs_supers.

Make sget_fc() skip SB_DEAD superblocks before invoking test(), and set
SB_DEAD under sb_lock to serialize with those callbacks. This allows
kernfs to free its private information after kill_anon_super() returns.
Keep matching SB_DYING superblocks until SB_DEAD is set so concurrent
mounts still wait for teardown before retrying.

Fixes: 43e15cdbef ("new helper: iterate_supers_type()")
Reported-by: Karl Mehltretter <kmehltretter@gmail.com>
Closes: https://lore.kernel.org/r/20260903013336.92081-1-kmehltretter@gmail.com
Suggested-by: Jan Kara <jack@suse.cz>
Cc: stable@vger.kernel.org
Tested-by: Karl Mehltretter <kmehltretter@gmail.com>
[kmehltretter: supplied the commit message]
Signed-off-by: Karl Mehltretter <kmehltretter@gmail.com>
Link: https://patch.msgid.link/20260909193034.7467-1-kmehltretter@gmail.com
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
2026-09-23 09:26:46 +02:00
..
dir.c kernfs: simplify kernfs_name_hash() 2026-07-18 16:07:22 +02:00
file.c kernfs: fix xattr race condition with multiple superblocks 2026-06-06 15:21:40 +02:00
inode.c kernfs: preserve security xattrs without allocating iattrs 2026-09-01 17:11:19 +02:00
Kconfig treewide: Add SPDX license identifier - Makefile/Kconfig 2019-05-21 10:50:46 +02:00
kernfs-internal.h simpe_xattr: use per-sb cache 2026-06-06 15:21:41 +02:00
Makefile treewide: Add SPDX license identifier - Makefile/Kconfig 2019-05-21 10:50:46 +02:00
mount.c super: make iterate_supers_type() deletion-safe 2026-09-23 09:26:46 +02:00
symlink.c kernfs: Replace strcpy(s, "../") with memcpy(s, "../", 4) 2026-07-18 16:07:22 +02:00