CVE-2026-72170

Status: UPDATED  |  Advisory ID: CVE-2026-72170

Key Details

Affected Products, Subsystems & Sectors

What to Know

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 [9p]

vfs_unlink+0x13c/0x258

...

In cacheless mode the server is authoritative and the inode is on its

way out, so locally adjusting nlink buys nothing. Skip v9fs_dec_count()

entirely when neither CACHE_META nor CACHE_LOOSE is set, which both

avoids the warning and removes a class of nlink races (two concurrent

unlinkers observing nlink > 0 and both calling drop_nlink()) that an

nlink == 0 guard alone would only narrow rather than close. (NVD)

What to Do

Monitor Linux's web page for any future patch releases.

References