CVE-2026-90400 md: recheck spare changes before starting sync
A race condition in the Linux kernel md driver allows a local attacker to trigger a NULL pointer dereference, causing a system crash.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-90400?
CVE-2026-90400 is a vulnerability in Linux, published on 17 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
md: recheck spare changes before starting sync
remove_spares() and remove_and_add_spares() modify the array's rdev configuration. These operations are only safe after the array has been suspended.
md_start_sync() checks whether spare configuration changes are needed before taking reconfig_mutex. However, the rdev state can change before the mutex is acquired, so the initial check can become stale. In that case, md_choose_sync_action() may remove or replace rdevs while normal I/O is still accessing them.
The race can occur as follows:
raid10d Worker Normal IO ____________ _______________________ ______________________
raid10_write_request() wait_blocked_dev() set Blocked set Faulty Skip Faulty rdev rrdev->nr_pending++ .repl_bio = bio removeable_rdev = false . array not suspended . lock mddev goto err_handle lock mddev (wait) . update sb . clear Blocked . . unlock mddev . lock mddev (acquires) remove_spares() removeable_rdev = true
raid10_remove_disk() rdev = replacement replacement = NULL rdev_dec_pending(NULL) unlock mddev (NULL)->nr_pending--
In this case, rdev_dec_pending() is called with a NULL pointer, resulting in a NULL pointer dereference when attempting to decrement nr_pending.
Fix this by suspending the array when spare configuration changes are needed, including for non-read-write arrays, and checking again after taking reconfig_mutex. If the array was not already suspended and a change is now needed, release the mutex, suspend the array, and reacquire the mutex before continuing.
Which versions are affected by CVE-2026-90400?
How do I fix CVE-2026-90400?
Apply the vendor's patch.
Is CVE-2026-90400 being exploited?
There is no known exploitation of CVE-2026-90400 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-90400, DEBIAN-CVE-2026-90400, GHSA-vwgq-hpcr-5x9r, UBUNTU-CVE-2026-90400.