CVE-2026-64112: rbd: eliminate a race in lock_dwork draining on unmap

From: Greg Kroah-Hartman <[email protected]>

Description
===========

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().

The Linux kernel CVE team has assigned CVE-2026-64112 to this issue.


Affected and fixed versions
===========================

	Fixed in 6.12.92 with commit 3427d7ae38337066ce88b68302e285d344ab756b
	Fixed in 6.18.34 with commit 9dcd4f5c99b491c37be90b0bd9988db48225fb75
	Fixed in 7.0.11 with commit 9400efc76b42c751211974a25c91d2c19c65b01b
	Fixed in 7.1 with commit 9fc75b71fdd38465c76c6f6a884cdd4ae3c72d90

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-64112
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	drivers/block/rbd.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/3427d7ae38337066ce88b68302e285d344ab756b
	https://git.kernel.org/stable/c/9dcd4f5c99b491c37be90b0bd9988db48225fb75
	https://git.kernel.org/stable/c/9400efc76b42c751211974a25c91d2c19c65b01b
	https://git.kernel.org/stable/c/9fc75b71fdd38465c76c6f6a884cdd4ae3c72d90