linux-cve-announce - CVE-2025-38415: Squashfs: check return result of sb_min

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Message-ID: <2025072513-CVE-2025-38415-c634@gregkh>
Date: Fri, 25 Jul 2025 15:32:14 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-38415: Squashfs: check return result of sb_min_blocksize

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

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

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

Squashfs: check return result of sb_min_blocksize

Syzkaller reports an "UBSAN: shift-out-of-bounds in squashfs_bio_read" bug.

Syzkaller forks multiple processes which after mounting the Squashfs
filesystem, issues an ioctl("/dev/loop0", LOOP_SET_BLOCK_SIZE, 0x8000). 
Now if this ioctl occurs at the same time another process is in the
process of mounting a Squashfs filesystem on /dev/loop0, the failure
occurs.  When this happens the following code in squashfs_fill_super()
fails.

----
msblk->devblksize = sb_min_blocksize(sb, SQUASHFS_DEVBLK_SIZE);
msblk->devblksize_log2 = ffz(~msblk->devblksize);
----

sb_min_blocksize() returns 0, which means msblk->devblksize is set to 0.

As a result, ffz(~msblk->devblksize) returns 64, and msblk->devblksize_log2
is set to 64.

This subsequently causes the

UBSAN: shift-out-of-bounds in fs/squashfs/block.c:195:36
shift exponent 64 is too large for 64-bit type 'u64' (aka
'unsigned long long')

This commit adds a check for a 0 return by sb_min_blocksize().

The Linux kernel CVE team has assigned CVE-2025-38415 to this issue.


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

	Issue introduced in 2.6.29 with commit 0aa666190509ffab81c202c5095a166be23961ac and fixed in 5.4.295 with commit db7096ea160e40d78c67fce52e7cc51bde049497
	Issue introduced in 2.6.29 with commit 0aa666190509ffab81c202c5095a166be23961ac and fixed in 5.10.239 with commit 549f9e3d7b60d53808c98b9fde49b4f46d0524a5
	Issue introduced in 2.6.29 with commit 0aa666190509ffab81c202c5095a166be23961ac and fixed in 5.15.186 with commit 5c51aa862cbeed2f3887f0382a2708956710bd68
	Issue introduced in 2.6.29 with commit 0aa666190509ffab81c202c5095a166be23961ac and fixed in 6.1.142 with commit 6abf6b78c6fb112eee495f5636ffcc350dd2ce25
	Issue introduced in 2.6.29 with commit 0aa666190509ffab81c202c5095a166be23961ac and fixed in 6.6.94 with commit 4f99357dadbf9c979ad737156ad4c37fadf7c56b
	Issue introduced in 2.6.29 with commit 0aa666190509ffab81c202c5095a166be23961ac and fixed in 6.12.34 with commit 0aff95d9bc7fb5400ca8af507429c4b067bdb425
	Issue introduced in 2.6.29 with commit 0aa666190509ffab81c202c5095a166be23961ac and fixed in 6.15.3 with commit 295ab18c2dbce8d0ac6ecf7c5187e16e1ac8b282
	Issue introduced in 2.6.29 with commit 0aa666190509ffab81c202c5095a166be23961ac and fixed in 6.16-rc1 with commit 734aa85390ea693bb7eaf2240623d41b03705c84

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-2025-38415
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/squashfs/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/db7096ea160e40d78c67fce52e7cc51bde049497
	https://git.kernel.org/stable/c/549f9e3d7b60d53808c98b9fde49b4f46d0524a5
	https://git.kernel.org/stable/c/5c51aa862cbeed2f3887f0382a2708956710bd68
	https://git.kernel.org/stable/c/6abf6b78c6fb112eee495f5636ffcc350dd2ce25
	https://git.kernel.org/stable/c/4f99357dadbf9c979ad737156ad4c37fadf7c56b
	https://git.kernel.org/stable/c/0aff95d9bc7fb5400ca8af507429c4b067bdb425
	https://git.kernel.org/stable/c/295ab18c2dbce8d0ac6ecf7c5187e16e1ac8b282
	https://git.kernel.org/stable/c/734aa85390ea693bb7eaf2240623d41b03705c84