linux-cve-announce - CVE-2025-21846: acct: perform last write from workqueue

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Message-ID: <2025031211-CVE-2025-21846-25c1@gregkh>
Date: Wed, 12 Mar 2025 10:42:12 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2025-21846: acct: perform last write from workqueue

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

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

acct: perform last write from workqueue

In [1] it was reported that the acct(2) system call can be used to
trigger NULL deref in cases where it is set to write to a file that
triggers an internal lookup. This can e.g., happen when pointing acc(2)
to /sys/power/resume. At the point the where the write to this file
happens the calling task has already exited and called exit_fs(). A
lookup will thus trigger a NULL-deref when accessing current->fs.

Reorganize the code so that the the final write happens from the
workqueue but with the caller's credentials. This preserves the
(strange) permission model and has almost no regression risk.

This api should stop to exist though.

The Linux kernel CVE team has assigned CVE-2025-21846 to this issue.


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

	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 6.1.130 with commit 5ee8da9bea70dda492d61f075658939af33d8410
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 6.6.80 with commit 5c928e14a2ccd99462f2351ead627b58075bb736
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 6.12.17 with commit 5a59ced8ffc71973d42c82484a719c8f6ac8f7f7
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 6.13.5 with commit a8136afca090412a36429cb6c2543c714d9c0f84
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 6.14-rc4 with commit 56d5f3eba3f5de0efdd556de4ef381e109b973a9

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-2025-21846
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:
	kernel/acct.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/5ee8da9bea70dda492d61f075658939af33d8410
	https://git.kernel.org/stable/c/5c928e14a2ccd99462f2351ead627b58075bb736
	https://git.kernel.org/stable/c/5a59ced8ffc71973d42c82484a719c8f6ac8f7f7
	https://git.kernel.org/stable/c/a8136afca090412a36429cb6c2543c714d9c0f84
	https://git.kernel.org/stable/c/56d5f3eba3f5de0efdd556de4ef381e109b973a9