Subject: CVE-2024-43914: md/raid5: avoid BUG_ON() while continue reshape after reassembling

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

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

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

md/raid5: avoid BUG_ON() while continue reshape after reassembling

Currently, mdadm support --revert-reshape to abort the reshape while
reassembling, as the test 07revert-grow. However, following BUG_ON()
can be triggerred by the test:

kernel BUG at drivers/md/raid5.c:6278!
invalid opcode: 0000 [#1] PREEMPT SMP PTI
irq event stamp: 158985
CPU: 6 PID: 891 Comm: md0_reshape Not tainted 6.9.0-03335-g7592a0b0049a #94
RIP: 0010:reshape_request+0x3f1/0xe60
Call Trace:
 <TASK>
 raid5_sync_request+0x43d/0x550
 md_do_sync+0xb7a/0x2110
 md_thread+0x294/0x2b0
 kthread+0x147/0x1c0
 ret_from_fork+0x59/0x70
 ret_from_fork_asm+0x1a/0x30
 </TASK>

Root cause is that --revert-reshape update the raid_disks from 5 to 4,
while reshape position is still set, and after reassembling the array,
reshape position will be read from super block, then during reshape the
checking of 'writepos' that is caculated by old reshape position will
fail.

Fix this panic the easy way first, by converting the BUG_ON() to
WARN_ON(), and stop the reshape if checkings fail.

Noted that mdadm must fix --revert-shape as well, and probably md/raid
should enhance metadata validation as well, however this means
reassemble will fail and there must be user tools to fix the wrong
metadata.

The Linux kernel CVE team has assigned CVE-2024-43914 to this issue.

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

	Fixed in 4.19.320 with commit 2c92f8c1c456
	Fixed in 5.4.282 with commit 6b33c468d543
	Fixed in 5.10.224 with commit c384dd4f1fb3
	Fixed in 5.15.165 with commit bf0ff69a42a3
	Fixed in 6.1.105 with commit 3b33740c1750
	Fixed in 6.6.46 with commit 775a9ba16c9f
	Fixed in 6.10.5 with commit 4811d6e5d9f4
	Fixed in 6.11 with commit 305a5170dc5c

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-2024-43914
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/raid5.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/2c92f8c1c456d556f15cbf51667b385026b2e6a0
	https://git.kernel.org/stable/c/6b33c468d543f6a83de2d61f09fec74b27e19fd2
	https://git.kernel.org/stable/c/c384dd4f1fb3b14a2fd199360701cc163ea88705
	https://git.kernel.org/stable/c/bf0ff69a42a3d2d46876d0514ecf13dffc516666
	https://git.kernel.org/stable/c/3b33740c1750a39e046339ff9240e954f0156707
	https://git.kernel.org/stable/c/775a9ba16c9ffe98fe54ebf14e55d5660f2bf600
	https://git.kernel.org/stable/c/4811d6e5d9f4090c3e0ff9890eb24077108046ab
	https://git.kernel.org/stable/c/305a5170dc5cf3d395bb4c4e9239bca6d0b54b49