CVE-2025-38709: linux kernel — Fix

Description

In the Linux kernel, the following vulnerability has been resolved: loop: Avoid updating block size under exclusive owner Syzbot came up with a reproducer where a loop device block size is changed underneath a mounted filesystem. This causes a mismatch between the block device block size and the block size stored in the superblock causing confusion in various places such as fs/buffer.c. The particular issue triggered by syzbot was a warning in __getblk_slow() due to requested buffer size not matching block device block size. Fix the problem by getting exclusive hold of the loop device to change its block size. This fails if somebody (such as filesystem) has already an exclusive ownership of the block device and thus prevents modifying the loop device under some exclusive owner which doesn't expect it.

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CVSS v3.1 Score

5.5

MEDIUM

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Affected Products

Vendor	Product	Versions
linux	linux_kernel	< 6.6.109
linux	linux_kernel	6.7 — 6.12.43
linux	linux_kernel	6.13 — 6.15.11
linux	linux_kernel	6.16 — 6.16.2

References

Advisories & Patches

https://git.kernel.org/stable/c/139a000d20f2f38ce34296feddd641d730fe1c08 https://git.kernel.org/stable/c/457d2c5e112fd08dc1039b1ae39a83ec1782360d https://git.kernel.org/stable/c/5d67b30aefeb7a949040bbb1b4e3b84c5d29a624 https://git.kernel.org/stable/c/7e49538288e523427beedd26993d446afef1a6fb https://git.kernel.org/stable/c/b928438cc87c0bf7ae078e4b7b6e14261e84c5c5

Frequently Asked Questions

What is CVE-2025-38709? +

In the Linux kernel, the following vulnerability has been resolved: loop: Avoid updating block size under exclusive owner Syzbot came up with a reproducer where a loop device block size is changed underneath a mounted filesystem. This causes a mismatch between the block device block size and the block size stored in the superblock causing confusion in various places such as fs/buffer.c. The particular issue triggered by syzbot was a warning in __getblk_slow() due to requested buffer size not matching block device block size. Fix the problem by getting exclusive hold of the loop device to change its block size. This fails if somebody (such as filesystem) has already an exclusive ownership of the block device and thus prevents modifying the loop device under some exclusive owner which doesn't expect it. It has a CVSS v3.1 base score of 5.5 (MEDIUM).

How severe is CVE-2025-38709? +

CVE-2025-38709 has a CVSS v3.1 score of 5.5 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance.

What products are affected by CVE-2025-38709? +

CVE-2025-38709 affects products from linux, specifically: linux_kernel. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2025-38709? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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