linux-cve-announce - CVE-2025-40305: 9p/trans_fd: p9_fd

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Message-ID: <2025120820-CVE-2025-40305-d66a@gregkh>
Date: Mon,  8 Dec 2025 09:47:29 +0900
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-40305: 9p/trans_fd: p9_fd_request: kick rx thread if EPOLLIN

From: Greg Kroah-Hartman <gregkh@...nel.org>

Description
===========

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

9p/trans_fd: p9_fd_request: kick rx thread if EPOLLIN

p9_read_work() doesn't set Rworksched and doesn't do schedule_work(m->rq)
if list_empty(&m->req_list).

However, if the pipe is full, we need to read more data and this used to
work prior to commit aaec5a95d59615 ("pipe_read: don't wake up the writer
if the pipe is still full").

p9_read_work() does p9_fd_read() -> ... -> anon_pipe_read() which (before
the commit above) triggered the unnecessary wakeup. This wakeup calls
p9_pollwake() which kicks p9_poll_workfn() -> p9_poll_mux(), p9_poll_mux()
will notice EPOLLIN and schedule_work(&m->rq).

This no longer happens after the optimization above, change p9_fd_request()
to use p9_poll_mux() instead of only checking for EPOLLOUT.

The Linux kernel CVE team has assigned CVE-2025-40305 to this issue.

Affected and fixed versions
===========================

	Fixed in 6.12.58 with commit 2e1461034aef99e905a1fe5589aaf00eaea73eee
	Fixed in 6.17.8 with commit 242531004d7de8c159f9bfadebe33fe8060b1046
	Fixed in 6.18 with commit e8fe3f07a357c39d429e02ca34f740692d88967a

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2025-40305
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	net/9p/trans_fd.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/2e1461034aef99e905a1fe5589aaf00eaea73eee
	https://git.kernel.org/stable/c/242531004d7de8c159f9bfadebe33fe8060b1046
	https://git.kernel.org/stable/c/e8fe3f07a357c39d429e02ca34f740692d88967a