CVE-2025-21807
MediumCVSS 5.5Exploitation Probability (EPSS)
Low risk2th percentile - higher than 2% of all known CVEs
Summary
A deadlock vulnerability (ABBA) was found in the Linux kernel's block layer when modifying queue limits via sysfs. The issue occurs when a user changes a limit (freezing the queue) while a device driver (e.g., SCSI sd) simultaneously revalidates limits, causing mutual blocking.
Risk Assessment
This deadlock can lead to a complete hang of the filesystem or block devices, resulting in denial of service (DoS) and potential data loss during critical I/O operations.
Recommendation
Immediately update the Linux kernel to a version containing the fix (commit that removes queue freezing before the store_limit method). For production systems, apply the security patch or upgrade to a stable kernel release with the fix.
Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: block: fix queue freeze vs limits lock order in sysfs store methods queue_attr_store() always freezes a device queue before calling the attribute store operation. For attributes that control queue limits, the store operation will also lock the queue limits with a call to queue_limits_start_update(). However, some drivers (e.g. SCSI sd) may need to issue commands to a device to obtain limit values from the hardware with the queue limits locked. This creates a potential ABBA deadlock situation if a user attempts to modify a limit (thus freezing the device queue) while the device driver starts a revalidation of the device queue limits. Avoid such deadlock by not freezing the queue before calling the ->store_limit() method in struct queue_sysfs_entry and instead use the queue_limits_commit_update_frozen helper to freeze the queue after taking the limits lock. This also removes taking the sysfs lock for the store_limit method as it doesn't protect anything here, but creates even more nesting. Hopefully it will go away from the actual sysfs methods entirely soon. (commit log adapted from a similar patch from Damien Le Moal)