CVE-2026-53125
Description
In the Linux kernel, the following vulnerability has been resolved:
md: fix array_state=clear sysfs deadlock
When "clear" is written to array_state, md_attr_store() breaks sysfs
active protection so the array can delete itself from its own sysfs
store method.
However, md_attr_store() currently drops the mddev reference before
calling sysfs_unbreak_active_protection(). Once do_md_stop(..., 0)
has made the mddev eligible for delayed deletion, the temporary
kobject reference taken by sysfs_break_active_protection() can become
the last kobject reference protecting the md kobject.
That allows sysfs_unbreak_active_protection() to drop the last
kobject reference from the current sysfs writer context. kobject
teardown then recurses into kernfs removal while the current sysfs
node is still being unwound, and lockdep reports recursive locking on
kn->active with kernfs_drain() in the call chain.
Reproducer on an existing level:
1. Create an md0 linear array and activate it:
mknod /dev/md0 b 9 0
echo none > /sys/block/md0/md/metadata_version
echo linear > /sys/block/md0/md/level
echo 1 > /sys/block/md0/md/raid_disks
echo "$(cat /sys/class/block/sdb/dev)" > /sys/block/md0/md/new_dev
echo "$(($(cat /sys/class/block/sdb/size) / 2))" > \
/sys/block/md0/md/dev-sdb/size
echo 0 > /sys/block/md0/md/dev-sdb/slot
echo active > /sys/block/md0/md/array_state
2. Wait briefly for the array to settle, then clear it:
sleep 2
echo clear > /sys/block/md0/md/array_state
The warning looks like:
WARNING: possible recursive locking detected
bash/588 is trying to acquire lock:
(kn->active#65) at __kernfs_remove+0x157/0x1d0
but task is already holding lock:
(kn->active#65) at sysfs_unbreak_active_protection+0x1f/0x40
...
Call Trace:
kernfs_drain
__kernfs_remove
kernfs_remove_by_name_ns
sysfs_remove_group
sysfs_remove_groups
__kobject_del
kobject_put
md_attr_store
kernfs_fop_write_iter
vfs_write
ksys_write
Restore active protection before mddev_put() so the extra sysfs
kobject reference is dropped while the mddev is still held alive. The
actual md kobject deletion is then deferred until after the sysfs
write path has fully returned.
Summary dbcve.org
A race condition in Linux kernel's MD (multiple device) subsystem causes a deadlock when clearing an array via sysfs. The issue occurs because md_attr_store() drops the mddev reference before calling sysfs_unbreak_active_protection(), allowing the kobject reference to become the last protection. This causes kobject teardown to recurse into kernfs removal while the sysfs node is still unwinding, triggering lockdep warnings for recursive locking on kn->active.
Mitigation
Apply the kernel patch that restores active protection before mddev_put() to defer md kobject deletion until after the sysfs write path completes. This is a kernel code fix requiring rebuild of the affected kernel modules.