Vulnerability CVE-2024-43914
Published: 2024-08-26

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.

 References:
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
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