linux-cve-announce - CVE-2025-40201: kernel/sys.c: fix the racy usage of task_lock(tsk->group_leader) in sys

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Message-ID: <2025111246-CVE-2025-40201-b8fe@gregkh>
Date: Wed, 12 Nov 2025 17:01:04 -0500
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-40201: kernel/sys.c: fix the racy usage of task_lock(tsk->group_leader) in sys_prlimit64() paths

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

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

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

kernel/sys.c: fix the racy usage of task_lock(tsk->group_leader) in sys_prlimit64() paths

The usage of task_lock(tsk->group_leader) in sys_prlimit64()->do_prlimit()
path is very broken.

sys_prlimit64() does get_task_struct(tsk) but this only protects task_struct
itself. If tsk != current and tsk is not a leader, this process can exit/exec
and task_lock(tsk->group_leader) may use the already freed task_struct.

Another problem is that sys_prlimit64() can race with mt-exec which changes
->group_leader. In this case do_prlimit() may take the wrong lock, or (worse)
->group_leader may change between task_lock() and task_unlock().

Change sys_prlimit64() to take tasklist_lock when necessary. This is not
nice, but I don't see a better fix for -stable.

The Linux kernel CVE team has assigned CVE-2025-40201 to this issue.


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

	Issue introduced in 5.18 with commit 18c91bb2d87268d23868bf13508f5bc9cf04e89a and fixed in 6.1.157 with commit 1bc0d9315ef5296abb2c9fd840336255850ded18
	Issue introduced in 5.18 with commit 18c91bb2d87268d23868bf13508f5bc9cf04e89a and fixed in 6.6.113 with commit 132f827e7bac7373e1522e89709d70b43cae5342
	Issue introduced in 5.18 with commit 18c91bb2d87268d23868bf13508f5bc9cf04e89a and fixed in 6.12.54 with commit 19b45c84bd9fd42fa97ff80c6350d604cb871c75
	Issue introduced in 5.18 with commit 18c91bb2d87268d23868bf13508f5bc9cf04e89a and fixed in 6.17.4 with commit 6796412decd2d8de8ec708213bbc958fab72f143
	Issue introduced in 5.18 with commit 18c91bb2d87268d23868bf13508f5bc9cf04e89a and fixed in 6.18-rc1 with commit a15f37a40145c986cdf289a4b88390f35efdecc4

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-2025-40201
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/sys.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/1bc0d9315ef5296abb2c9fd840336255850ded18
	https://git.kernel.org/stable/c/132f827e7bac7373e1522e89709d70b43cae5342
	https://git.kernel.org/stable/c/19b45c84bd9fd42fa97ff80c6350d604cb871c75
	https://git.kernel.org/stable/c/6796412decd2d8de8ec708213bbc958fab72f143
	https://git.kernel.org/stable/c/a15f37a40145c986cdf289a4b88390f35efdecc4