linux-cve-announce - CVE-2025-40249: gpio: cdev: make sure the cdev fd is still active before emitting events

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Message-ID: <2025120430-CVE-2025-40249-3972@gregkh>
Date: Thu,  4 Dec 2025 16:57:30 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-40249: gpio: cdev: make sure the cdev fd is still active before emitting events

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

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

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

gpio: cdev: make sure the cdev fd is still active before emitting events

With the final call to fput() on a file descriptor, the release action
may be deferred and scheduled on a work queue. The reference count of
that descriptor is still zero and it must not be used. It's possible
that a GPIO change, we want to notify the user-space about, happens
AFTER the reference count on the file descriptor associated with the
character device went down to zero but BEFORE the .release() callback
was called from the workqueue and so BEFORE we unregistered from the
notifier.

Using the regular get_file() routine in this situation triggers the
following warning:

  struct file::f_count incremented from zero; use-after-free condition present!

So use the get_file_active() variant that will return NULL on file
descriptors that have been or are being released.

The Linux kernel CVE team has assigned CVE-2025-40249 to this issue.

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

	Issue introduced in 6.13 with commit 40b7c49950bd56c984b1f6722f865b922879260e and fixed in 6.17.10 with commit dccc6daa8afa0f64c432e4c867f275747e3415e1
	Issue introduced in 6.13 with commit 40b7c49950bd56c984b1f6722f865b922879260e and fixed in 6.18 with commit d4cd0902c156b2ca60fdda8cd8b5bcb4b0e9ed64

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-2025-40249
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:
	drivers/gpio/gpiolib-cdev.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/dccc6daa8afa0f64c432e4c867f275747e3415e1
	https://git.kernel.org/stable/c/d4cd0902c156b2ca60fdda8cd8b5bcb4b0e9ed64