CVE-2025-38058: __legitimize_mnt(): check for MNT_SYNC_UMOUNT should be under mount_lock

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-06-18 · updated 2026-10-15
Weakness: CWE-667

Description

In the Linux kernel, the following vulnerability has been resolved: __legitimize_mnt(): check for MNT_SYNC_UMOUNT should be under mount_lock ... or we risk stealing final mntput from sync umount - raising mnt_count after umount(2) has verified that victim is not busy, but before it has set MNT_SYNC_UMOUNT; in that case __legitimize_mnt() doesn't see that it's safe to quietly undo mnt_count increment and leaves dropping the reference to caller, where it'll be a full-blown mntput(). Check under mount_lock is needed; leaving the current one done before taking that makes no sense - it's nowhere near common enough to bother with.

Affected products

Debian Linux: 11.0
Linux kernel: before 5.4.294; from 5.5 before 5.10.238; from 5.11 before 5.15.185; from 5.16 before 6.1.141; from 6.2 before 6.6.93; from 6.7 before 6.12.31 — fixed in 5.10.238, 5.15.185, 5.4.294, 6.1.141, 6.12.31, 6.14.9

How to fix

Upgrade to a fixed version: Linux kernel 5.10.238, 5.15.185, 5.4.294, 6.1.141. Check the vendor advisory for mitigations.

References

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