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md: reject v0.90 arrays with too many devices

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The v0.90 superblock has room for MD_SB_DISKS device descriptors, but
super_90_load() only rejects nonpositive raid_disks values. A crafted
superblock can therefore copy a larger value into mddev->raid_disks. When
metadata is next updated, super_90_sync() walks sb->disks[] up to that
count and reads and writes beyond the 4 KiB superblock buffer.

A checksum-valid RAID1 member advertising 64 devices can be assembled by
mdadm --incremental --run. The first write to the array then produces
out-of-bounds writes from super_90_sync() under KASAN.

Reject device counts that cannot be represented by the v0.90 format while
loading the superblock.

Assisted-by: Codex:gpt-5
Signed-off-by: Jérémy Jean <Jeremy.Jean@oss.cyber.gouv.fr>
Fixes: 1da177e4c3 ("Linux-2.6.12-rc2")
Link: https://patch.msgid.link/20260820210703.3035608-2-Jeremy.Jean@oss.cyber.gouv.fr
Signed-off-by: Yu Kuai <yukuai@fygo.io>
This commit is contained in:
Jérémy Jean 2026-08-20 21:07:03 +00:00 committed by Yu Kuai
parent f00eb0ff45
commit 1a33a379e6
1 changed files with 1 additions and 1 deletions
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2
drivers/md/md.c
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@ -1393,7 +1393,7 @@ static int super_90_load(struct md_rdev *rdev, struct md_rdev *refdev, int minor
goto abort;
}
if (sb->raid_disks <= 0)
if (sb->raid_disks <= 0 || sb->raid_disks > MD_SB_DISKS)
goto abort;
if (md_csum_fold(calc_sb_csum(sb)) != md_csum_fold(sb->sb_csum)) {