From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-cve-announce@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@kernel.org>
Subject: CVE-2026-43288: ext4: move ext4_percpu_param_init() before ext4_mb_init()
Date: Fri, 8 May 2026 15:11:53 +0200 [thread overview]
Message-ID: <2026050851-CVE-2026-43288-7514@gregkh> (raw)
From: Greg Kroah-Hartman <gregkh@kernel.org>
Description
===========
In the Linux kernel, the following vulnerability has been resolved:
ext4: move ext4_percpu_param_init() before ext4_mb_init()
When running `kvm-xfstests -c ext4/1k -C 1 generic/383` with the
`DOUBLE_CHECK` macro defined, the following panic is triggered:
==================================================================
EXT4-fs error (device vdc): ext4_validate_block_bitmap:423:
comm mount: bg 0: bad block bitmap checksum
BUG: unable to handle page fault for address: ff110000fa2cc000
PGD 3e01067 P4D 3e02067 PUD 0
Oops: Oops: 0000 [#1] SMP NOPTI
CPU: 0 UID: 0 PID: 2386 Comm: mount Tainted: G W
6.18.0-gba65a4e7120a-dirty #1152 PREEMPT(none)
RIP: 0010:percpu_counter_add_batch+0x13/0xa0
Call Trace:
<TASK>
ext4_mark_group_bitmap_corrupted+0xcb/0xe0
ext4_validate_block_bitmap+0x2a1/0x2f0
ext4_read_block_bitmap+0x33/0x50
mb_group_bb_bitmap_alloc+0x33/0x80
ext4_mb_add_groupinfo+0x190/0x250
ext4_mb_init_backend+0x87/0x290
ext4_mb_init+0x456/0x640
__ext4_fill_super+0x1072/0x1680
ext4_fill_super+0xd3/0x280
get_tree_bdev_flags+0x132/0x1d0
vfs_get_tree+0x29/0xd0
vfs_cmd_create+0x59/0xe0
__do_sys_fsconfig+0x4f6/0x6b0
do_syscall_64+0x50/0x1f0
entry_SYSCALL_64_after_hwframe+0x76/0x7e
==================================================================
This issue can be reproduced using the following commands:
mkfs.ext4 -F -q -b 1024 /dev/sda 5G
tune2fs -O quota,project /dev/sda
mount /dev/sda /tmp/test
With DOUBLE_CHECK defined, mb_group_bb_bitmap_alloc() reads
and validates the block bitmap. When the validation fails,
ext4_mark_group_bitmap_corrupted() attempts to update
sbi->s_freeclusters_counter. However, this percpu_counter has not been
initialized yet at this point, which leads to the panic described above.
Fix this by moving the execution of ext4_percpu_param_init() to occur
before ext4_mb_init(), ensuring the per-CPU counters are initialized
before they are used.
The Linux kernel CVE team has assigned CVE-2026-43288 to this issue.
Affected and fixed versions
===========================
Fixed in 6.6.128 with commit 0d5fcb063cdabb9aeaa8554b7fedad2092c4150e
Fixed in 6.12.75 with commit 9e9fb259bcddf459a0168f4a964e979e500a68a5
Fixed in 6.18.16 with commit bf5b609524497c195f801cd5707252384aed8149
Fixed in 6.19.6 with commit aec095f3cc6cf209effd93278ce35be27db81d73
Fixed in 7.0 with commit 270564513489d98b721a1e4a10017978d5213bff
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-2026-43288
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:
fs/ext4/super.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/0d5fcb063cdabb9aeaa8554b7fedad2092c4150e
https://git.kernel.org/stable/c/9e9fb259bcddf459a0168f4a964e979e500a68a5
https://git.kernel.org/stable/c/bf5b609524497c195f801cd5707252384aed8149
https://git.kernel.org/stable/c/aec095f3cc6cf209effd93278ce35be27db81d73
https://git.kernel.org/stable/c/270564513489d98b721a1e4a10017978d5213bff
reply other threads:[~2026-05-08 13:15 UTC|newest]
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