CVE-2025-40125 blk-mq: check kobject state_in_sysfs before deleting in blk_mq_unregister_hctx
A local attacker with high privileges can trigger a kernel warning and potential denial of service by manipulating block device queue settings after a sysfs registration failure.
- Exploited in the wild
- Not known
- Login needed
- An administrator
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-40125?
CVE-2025-40125 is a vulnerability in Linux, published on 12 Nov 2025. 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:
blk-mq: check kobject state_in_sysfs before deleting in blk_mq_unregister_hctx
In __blk_mq_update_nr_hw_queues() the return value of blk_mq_sysfs_register_hctxs() is not checked. If sysfs creation for hctx fails, later changing the number of hw_queues or removing disk will trigger the following warning:
kernfs: can not remove 'nr_tags', no directory WARNING: CPU: 2 PID: 637 at fs/kernfs/dir.c:1707 kernfs_remove_by_name_ns+0x13f/0x160 Call Trace: remove_files.isra.1+0x38/0xb0 sysfs_remove_group+0x4d/0x100 sysfs_remove_groups+0x31/0x60 __kobject_del+0x23/0xf0 kobject_del+0x17/0x40 blk_mq_unregister_hctx+0x5d/0x80 blk_mq_sysfs_unregister_hctxs+0x94/0xd0 blk_mq_update_nr_hw_queues+0x124/0x760 nullb_update_nr_hw_queues+0x71/0xf0 [null_blk] nullb_device_submit_queues_store+0x92/0x120 [null_blk]
kobjct_del() was called unconditionally even if sysfs creation failed. Fix it by checkig the kobject creation statusbefore deleting it.
Which versions are affected by CVE-2025-40125?
How do I fix CVE-2025-40125?
Apply the vendor's patch.
Is CVE-2025-40125 being exploited?
There is no known exploitation of CVE-2025-40125 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2025-40125, DEBIAN-CVE-2025-40125, GHSA-8mqf-xr44-qqq9, ROOT-OS-UBUNTU-2404-CVE-2025-40125, UBUNTU-CVE-2025-40125.