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.
History

Fri, 05 Sep 2025 14:15:00 +0000

Type Values Removed Values Added
First Time appeared Linux
Linux linux Kernel
Vendors & Products Linux
Linux linux Kernel

Fri, 05 Sep 2025 00:15:00 +0000

Type Values Removed Values Added
References
Metrics threat_severity

None

cvssV3_1

{'score': 7.0, 'vector': 'CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H'}

threat_severity

Moderate


Thu, 04 Sep 2025 15:45:00 +0000

Type Values Removed Values Added
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.
Title loop: Avoid updating block size under exclusive owner
References

cve-icon MITRE

Status: PUBLISHED

Assigner: Linux

Published:

Updated: 2025-09-04T15:32:59.818Z

Reserved: 2025-04-16T04:51:24.033Z

Link: CVE-2025-38709

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Awaiting Analysis

Published: 2025-09-04T16:15:39.997

Modified: 2025-09-05T17:47:24.833

Link: CVE-2025-38709

cve-icon Redhat

Severity : Moderate

Publid Date: 2025-09-04T00:00:00Z

Links: CVE-2025-38709 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2025-09-05T14:02:40Z