linux-cve-announce - CVE-2025-38496: dm-bufio: fix sched in atomic context

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Message-ID: <2025072818-CVE-2025-38496-4301@gregkh>
Date: Mon, 28 Jul 2025 13:22:38 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-38496: dm-bufio: fix sched in atomic context

From: Greg Kroah-Hartman <gregkh@...nel.org>

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

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

dm-bufio: fix sched in atomic context

If "try_verify_in_tasklet" is set for dm-verity, DM_BUFIO_CLIENT_NO_SLEEP
is enabled for dm-bufio. However, when bufio tries to evict buffers, there
is a chance to trigger scheduling in spin_lock_bh, the following warning
is hit:

BUG: sleeping function called from invalid context at drivers/md/dm-bufio.c:2745
in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 123, name: kworker/2:2
preempt_count: 201, expected: 0
RCU nest depth: 0, expected: 0
4 locks held by kworker/2:2/123:
 #0: ffff88800a2d1548 ((wq_completion)dm_bufio_cache){....}-{0:0}, at: process_one_work+0xe46/0x1970
 #1: ffffc90000d97d20 ((work_completion)(&dm_bufio_replacement_work)){....}-{0:0}, at: process_one_work+0x763/0x1970
 #2: ffffffff8555b528 (dm_bufio_clients_lock){....}-{3:3}, at: do_global_cleanup+0x1ce/0x710
 #3: ffff88801d5820b8 (&c->spinlock){....}-{2:2}, at: do_global_cleanup+0x2a5/0x710
Preemption disabled at:
[<0000000000000000>] 0x0
CPU: 2 UID: 0 PID: 123 Comm: kworker/2:2 Not tainted 6.16.0-rc3-g90548c634bd0 #305 PREEMPT(voluntary)
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
Workqueue: dm_bufio_cache do_global_cleanup
Call Trace:
 <TASK>
 dump_stack_lvl+0x53/0x70
 __might_resched+0x360/0x4e0
 do_global_cleanup+0x2f5/0x710
 process_one_work+0x7db/0x1970
 worker_thread+0x518/0xea0
 kthread+0x359/0x690
 ret_from_fork+0xf3/0x1b0
 ret_from_fork_asm+0x1a/0x30
 </TASK>

That can be reproduced by:

  veritysetup format --data-block-size=4096 --hash-block-size=4096 /dev/vda /dev/vdb
  SIZE=$(blockdev --getsz /dev/vda)
  dmsetup create myverity -r --table "0 $SIZE verity 1 /dev/vda /dev/vdb 4096 4096 <data_blocks> 1 sha256 <root_hash> <salt> 1 try_verify_in_tasklet"
  mount /dev/dm-0 /mnt -o ro
  echo 102400 > /sys/module/dm_bufio/parameters/max_cache_size_bytes
  [read files in /mnt]

The Linux kernel CVE team has assigned CVE-2025-38496 to this issue.


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

	Issue introduced in 6.4 with commit 450e8dee51aa6fa1dd0f64073e88235f1a77b035 and fixed in 6.6.100 with commit 469a39a33a9934af157299bf11c58f6e6cb53f85
	Issue introduced in 6.4 with commit 450e8dee51aa6fa1dd0f64073e88235f1a77b035 and fixed in 6.12.40 with commit 68860d1ade385eef9fcdbf6552f061283091fdb8
	Issue introduced in 6.4 with commit 450e8dee51aa6fa1dd0f64073e88235f1a77b035 and fixed in 6.15.8 with commit 3edfdb1d4ef81320dae0caa40bc24baf8c1bbb86
	Issue introduced in 6.4 with commit 450e8dee51aa6fa1dd0f64073e88235f1a77b035 and fixed in 6.16 with commit b1bf1a782fdf5c482215c0c661b5da98b8e75773

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-2025-38496
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/dm-bufio.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/469a39a33a9934af157299bf11c58f6e6cb53f85
	https://git.kernel.org/stable/c/68860d1ade385eef9fcdbf6552f061283091fdb8
	https://git.kernel.org/stable/c/3edfdb1d4ef81320dae0caa40bc24baf8c1bbb86
	https://git.kernel.org/stable/c/b1bf1a782fdf5c482215c0c661b5da98b8e75773