Subject: CVE-2024-40925: block: fix request.queuelist usage in flush

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

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

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

block: fix request.queuelist usage in flush

Friedrich Weber reported a kernel crash problem and bisected to commit
81ada09cc25e ("blk-flush: reuse rq queuelist in flush state machine").

The root cause is that we use "list_move_tail(&rq->queuelist, pending)"
in the PREFLUSH/POSTFLUSH sequences. But rq->queuelist.next == xxx since
it's popped out from plug->cached_rq in __blk_mq_alloc_requests_batch().
We don't initialize its queuelist just for this first request, although
the queuelist of all later popped requests will be initialized.

Fix it by changing to use "list_add_tail(&rq->queuelist, pending)" so
rq->queuelist doesn't need to be initialized. It should be ok since rq
can't be on any list when PREFLUSH or POSTFLUSH, has no move actually.

Please note the commit 81ada09cc25e ("blk-flush: reuse rq queuelist in
flush state machine") also has another requirement that no drivers would
touch rq->queuelist after blk_mq_end_request() since we will reuse it to
add rq to the post-flush pending list in POSTFLUSH. If this is not true,
we will have to revert that commit IMHO.

This updated version adds "list_del_init(&rq->queuelist)" in flush rq
callback since the dm layer may submit request of a weird invalid format
(REQ_FSEQ_PREFLUSH | REQ_FSEQ_POSTFLUSH), which causes double list_add
if without this "list_del_init(&rq->queuelist)". The weird invalid format
problem should be fixed in dm layer.

The Linux kernel CVE team has assigned CVE-2024-40925 to this issue.

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

	Issue introduced in 6.6 with commit 81ada09cc25e and fixed in 6.6.35 with commit fe1e395563cc
	Issue introduced in 6.6 with commit 81ada09cc25e and fixed in 6.9.6 with commit 87907bd69721
	Issue introduced in 6.6 with commit 81ada09cc25e and fixed in 6.10 with commit d0321c812d89

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-2024-40925
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:
	block/blk-flush.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/fe1e395563ccb051e9dbd8fa99859f5caaad2e71
	https://git.kernel.org/stable/c/87907bd69721a8506618a954d41a1de3040e88aa
	https://git.kernel.org/stable/c/d0321c812d89c5910d8da8e4b10c891c6b96ff70