CVE-2026-64112 in Linux
Summary
by MITRE • 07/19/2026
In the Linux kernel, the following vulnerability has been resolved:
rbd: eliminate a race in lock_dwork draining on unmap
Given how rbd_lock_add_request() and rbd_img_exclusive_lock() are written, lock_dwork may be (re)queued more than it's actually needed: for example in case a new I/O request comes in while we are in the middle of rbd_acquire_lock() on behalf of another I/O request. This is expected and with rbd_release_lock() preemptively canceling lock_dwork is benign under normal operation.
A more problematic example is maybe_kick_acquire():
if (have_requests || delayed_work_pending(&rbd_dev->lock_dwork)) {
dout("%s rbd_dev %p kicking lock_dwork\n", __func__, rbd_dev); mod_delayed_work(rbd_dev->task_wq, &rbd_dev->lock_dwork, 0); }
It's not unrealistic for lock_dwork to get canceled right after delayed_work_pending() returns true and for mod_delayed_work() to requeue it right there anyway. This is a classic TOCTOU race.
When it comes to unmapping the image, there is an implicit assumption of no self-initiated exclusive lock activity past the point of return from rbd_dev_image_unlock() which unlocks the lock if it happens to be held. This unlock is assumed to be final and lock_dwork (as well as all other exclusive lock tasks, really) isn't expected to get queued again. However, lock_dwork is canceled only in cancel_tasks_sync() (i.e. later in the unmap sequence) and on top of that the cancellation can get in effect nullified by maybe_kick_acquire(). This may result in rbd_acquire_lock() executing after rbd_dev_device_release() and rbd_dev_image_release() run and free and/or reset a bunch of things. One of the possible failure modes then is a violated
rbd_assert(rbd_image_format_valid(rbd_dev->image_format));
in rbd_dev_header_info() which is called via rbd_dev_refresh() from rbd_post_acquire_action().
Redo exclusive lock task draining to provide saner semantics and try to meet the assumptions around rbd_dev_image_unlock().
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Analysis
by VulDB Data Team • 07/19/2026
The vulnerability in the Linux kernel's rbd (RADOS Block Device) subsystem stems from a race condition during the lock_dwork draining process when unmapping RBD images. This issue manifests through improper handling of exclusive lock operations that can lead to memory corruption and system instability. The root cause lies in how the rbd_lock_add_request() and rbd_img_exclusive_lock() functions manage delayed work queuing, creating scenarios where lock_dwork may be unnecessarily requeued multiple times during concurrent I/O operations.
The race condition becomes particularly problematic in the maybe_kick_acquire() function where a time-of-check to time-of-use vulnerability exists. When delayed_work_pending() returns true and immediately followed by mod_delayed_work() requeuing the work, there's a window where the cancellation of lock_dwork can occur after the check but before the requeue operation. This TOCTOU race condition is classified as CWE-367 and represents a classic timing attack scenario that can be exploited to disrupt normal operation sequences.
During the unmap sequence, the system assumes that no self-initiated exclusive lock activities will occur after rbd_dev_image_unlock() completes its operation. However, this assumption breaks down when lock_dwork cancellation in cancel_tasks_sync() occurs after the unlock operation but before all potential requeuing operations are completed. The race condition allows rbd_acquire_lock() to execute after rbd_dev_device_release() and rbd_dev_image_release() have already freed or reset critical data structures, creating a scenario where memory references become invalid.
The most significant failure mode occurs when rbd_dev_header_info() is called via rbd_dev_refresh() from rbd_post_acquire_action(), resulting in a violated assertion that checks rbd_image_format_valid(rbd_dev->image_format). This condition directly violates security assumptions about data integrity and can lead to kernel panics or memory corruption. The vulnerability affects the fundamental operational semantics of exclusive lock task draining, where the expected behavior of immediate task completion is not guaranteed, leading to inconsistent system states.
The solution requires a complete redesign of the exclusive lock task draining mechanism to provide more predictable and safer semantics. This involves ensuring that all lock_dwork operations are properly synchronized with the unmap sequence and that no stale references persist after resource cleanup has occurred. The fix must address the implicit assumptions about lock state management during device release and ensure proper ordering of operations to prevent the execution of lock acquisition functions against freed memory structures, thereby maintaining system stability and preventing potential privilege escalation or denial of service conditions.