---
id: CVE-2026-63795
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  9p: avoid putting oldfid in p9_client_walk() error path

  When p9_client_walk() is called with clone set to false, fid aliases
  oldfid
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  9p: avoid putting oldfid in p9_client_walk() error path

  When p9_client_walk() is called with clone set to false, fid aliases
  oldfid. If the walk subsequently fails aft…
severity: none
published: '2026-07-19'
updated: '2026-07-19'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-63795'
references:
  - url: 'https://git.kernel.org/stable/c/1a3860d46e3eb47dbd60339783cdad7904486b9f'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/6dbe9443d9f5f7fb6d319a7b77108853ae6c6bea'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/99c379ca1e221c3d75c7c804ebbf4e5ee37a3070'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/a61bdcba4f64c2f90d01461913f429ab151f1ca6'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/a7656d368265d085ac9bb85ab31b0cdb72ad8c38'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/b84f46179c806450b89821221ea5bd9a1698aba8'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
tags:
  - nvd
ingestedAt: '2026-07-19T23:34:10.645Z'
epss: 0.00504
epssPercentile: 0.40511
---

## Overview

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

9p: avoid putting oldfid in p9_client_walk() error path

When p9_client_walk() is called with clone set to false, fid aliases
oldfid. If the walk subsequently fails after the request has been sent,
the error path jumps to clunk_fid, which currently calls p9_fid_put(fid)
unconditionally.

This drops a reference to oldfid even though ownership of oldfid remains
with the caller. If this is the last reference, oldfid can be clunked and
destroyed while the caller still expects it to be valid. A later use or
put of oldfid can then trigger a use-after-free or refcount underflow.

Fix this by only putting fid in the clunk_fid error path when it does not
alias oldfid, matching the existing guard in the error path below.

This can be triggered when a multi-component walk is split into multiple
p9_client_walk() calls and a later non-cloning walk fails. A reproducer
and refcount warning logs are available on request.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.