PT-2026-61111 · Linux · Linux

CVE-2026-63795 · Published 2026-07-19 · Updated 2026-07-19

NVD

CVSS v3.1

10

Critical

Base vector

AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

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.

Fix

Related Identifiers

CVE-2026-63795

Affected Products

Linux

References · 7

• https://nvd.nist.gov/vuln/detail/CVE-2026-63795 · Security Note
• https://git.kernel.org/stable/c/a61bdcba4f64c2f90d01461913f429ab151f1ca6 · Note
• https://git.kernel.org/stable/c/1a3860d46e3eb47dbd60339783cdad7904486b9f · Note
• https://git.kernel.org/stable/c/b84f46179c806450b89821221ea5bd9a1698aba8 · Note
• https://git.kernel.org/stable/c/6dbe9443d9f5f7fb6d319a7b77108853ae6c6bea · Note
• https://git.kernel.org/stable/c/a7656d368265d085ac9bb85ab31b0cdb72ad8c38 · Note
• https://git.kernel.org/stable/c/99c379ca1e221c3d75c7c804ebbf4e5ee37a3070 · Note