CVE-2026-72170

Technical Description

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

9p: skip nlink update in cacheless mode to fix WARN_ON

v9fs_dec_count() unconditionally calls drop_nlink() on regular files,

even when the inode's nlink is already zero. In cacheless mode the

client refetches inode metadata from the server (the source of truth)

on every operation, so by the time v9fs_remove() returns, the locally

cached nlink may already reflect the post-unlink value:

1. Client initiates unlink, server processes it and sets nlink to 0

2. Client refetches inode metadata (nlink=0) before unlink returns

3. Client's v9fs_remove() completes successfully

4. Client calls v9fs_dec_count() which calls drop_nlink() on nlink=0

This race is easily triggered under heavy unlink workloads, such as

stress-ng's unlink stressor, producing the following warning:

WARNING: fs/inode.c:417 at drop_nlink+0x4c/0xc8

Call trace:

drop_nlink+0x4c/0xc8

v9fs_remove+0x1e0/0x250 [9p]

v9fs_vfs_unlink+0x20/0x38

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References