CVE-2025-68823

In the Linux kernel, the following vulnerability has been resolved:

ublk: fix deadlock when reading partition table

When one process(such as udev) opens ublk block device (e.g., to read the partition table via bdev_open()), a deadlock[1] can occur:

1. bdev_open() grabs disk->open_mutex
2. The process issues read I/O to ublk backend to read partition table
3. In __ublk_complete_rq(), blk_update_request() or blk_mq_end_request() runs bio->bi_end_io() callbacks
4. If this triggers fput() on file descriptor of ublk block device, the work may be deferred to current tasks task work (see fput() implementation)
5. This eventually calls blkdev_release() from the same context
6. blkdev_release() tries to grab disk->open_mutex again
7. Deadlock: same task waiting for a mutex it already holds

The fix is to run blk_update_request() and blk_mq_end_request() with bottom halves disabled. This forces blkdev_release() to run in kernel work-queue context instead of current task work context, and allows ublk server to make forward progress, and avoids the deadlock.

[axboe: rewrite comment in ublk]

Weakness

The product does not properly acquire or release a lock on a resource, leading to unexpected resource state changes and behaviors.

Affected Software

Extended Description

Locking is a type of synchronization behavior that ensures that multiple independently-operating processes or threads do not interfere with each other when accessing the same resource. All processes/threads are expected to follow the same steps for locking. If these steps are not followed precisely - or if no locking is done at all - then another process/thread could modify the shared resource in a way that is not visible or predictable to the original process. This can lead to data or memory corruption, denial of service, etc.

Potential Mitigations

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/25.html
• https://cwe.mitre.org/data/definitions/26.html
• https://cwe.mitre.org/data/definitions/27.html

References

• https://git.kernel.org/stable/c/0460e09a614291f06c008443f47393c37b7358e7
• https://git.kernel.org/stable/c/64c0b7e2293757e8320f13434cd809f1c9257a62
• https://git.kernel.org/stable/c/9bcc47343ee0ef346aa7b2b460c8ff56bd882fe7
• https://git.kernel.org/stable/c/c258f5c4502c9667bccf5d76fa731ab9c96687c1