Subject: CVE-2024-26718: dm-crypt, dm-verity: disable tasklets

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

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

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

dm-crypt, dm-verity: disable tasklets

Tasklets have an inherent problem with memory corruption. The function
tasklet_action_common calls tasklet_trylock, then it calls the tasklet
callback and then it calls tasklet_unlock. If the tasklet callback frees
the structure that contains the tasklet or if it calls some code that may
free it, tasklet_unlock will write into free memory.

The commits 8e14f610159d and d9a02e016aaf try to fix it for dm-crypt, but
it is not a sufficient fix and the data corruption can still happen [1].
There is no fix for dm-verity and dm-verity will write into free memory
with every tasklet-processed bio.

There will be atomic workqueues implemented in the kernel 6.9 [2]. They
will have better interface and they will not suffer from the memory
corruption problem.

But we need something that stops the memory corruption now and that can be
backported to the stable kernels. So, I'm proposing this commit that
disables tasklets in both dm-crypt and dm-verity. This commit doesn't
remove the tasklet support, because the tasklet code will be reused when
atomic workqueues will be implemented.

[1] https://lore.kernel.org/all/[email-masked]/T/
[2] https://lore.kernel.org/lkml/[email-masked]/

The Linux kernel CVE team has assigned CVE-2024-26718 to this issue.

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

	Issue introduced in 5.9 with commit 39d42fa96ba1 and fixed in 5.15.169 with commit b825e0f9d68c
	Issue introduced in 5.9 with commit 39d42fa96ba1 and fixed in 6.1.79 with commit 30884a44e0ce
	Issue introduced in 5.9 with commit 39d42fa96ba1 and fixed in 6.6.18 with commit 5735a2671ffb
	Issue introduced in 5.9 with commit 39d42fa96ba1 and fixed in 6.7.6 with commit 0c45a20cbe68
	Issue introduced in 5.9 with commit 39d42fa96ba1 and fixed in 6.8 with commit 0a9bab391e33

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-2024-26718
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/md/dm-crypt.c
	drivers/md/dm-verity-target.c
	drivers/md/dm-verity.h

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/b825e0f9d68c178072bffd32dd34c39e3d2d597a
	https://git.kernel.org/stable/c/30884a44e0cedc3dfda8c22432f3ba4078ec2d94
	https://git.kernel.org/stable/c/5735a2671ffb70ea29ca83969fe01316ee2ed6fc
	https://git.kernel.org/stable/c/0c45a20cbe68bc4d681734f5c03891124a274257
	https://git.kernel.org/stable/c/0a9bab391e336489169b95cb0d4553d921302189