linux-cve-announce - CVE-2025-21857: net/sched: cls_api: fix error handling causing NULL dereference

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Message-ID: <2025031215-CVE-2025-21857-ab00@gregkh>
Date: Wed, 12 Mar 2025 10:42:23 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2025-21857: net/sched: cls_api: fix error handling causing NULL dereference

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

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

net/sched: cls_api: fix error handling causing NULL dereference

tcf_exts_miss_cookie_base_alloc() calls xa_alloc_cyclic() which can
return 1 if the allocation succeeded after wrapping. This was treated as
an error, with value 1 returned to caller tcf_exts_init_ex() which sets
exts->actions to NULL and returns 1 to caller fl_change().

fl_change() treats err == 1 as success, calling tcf_exts_validate_ex()
which calls tcf_action_init() with exts->actions as argument, where it
is dereferenced.

Example trace:

BUG: kernel NULL pointer dereference, address: 0000000000000000
CPU: 114 PID: 16151 Comm: handler114 Kdump: loaded Not tainted 5.14.0-503.16.1.el9_5.x86_64 #1
RIP: 0010:tcf_action_init+0x1f8/0x2c0
Call Trace:
 tcf_action_init+0x1f8/0x2c0
 tcf_exts_validate_ex+0x175/0x190
 fl_change+0x537/0x1120 [cls_flower]

The Linux kernel CVE team has assigned CVE-2025-21857 to this issue.


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

	Issue introduced in 6.3 with commit 80cd22c35c9001fe72bf614d29439de41933deca and fixed in 6.6.80 with commit de4b679aa3b4da7ec34f639df068b914f20e3c3c
	Issue introduced in 6.3 with commit 80cd22c35c9001fe72bf614d29439de41933deca and fixed in 6.12.17 with commit 3e4c56cf41876ef2a82f0877fe2a67648f8632b8
	Issue introduced in 6.3 with commit 80cd22c35c9001fe72bf614d29439de41933deca and fixed in 6.13.5 with commit 3c74b5787caf59bb1e9c5fe0a360643a71eb1e8a
	Issue introduced in 6.3 with commit 80cd22c35c9001fe72bf614d29439de41933deca and fixed in 6.14-rc4 with commit 071ed42cff4fcdd89025d966d48eabef59913bf2

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-2025-21857
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/sched/cls_api.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/de4b679aa3b4da7ec34f639df068b914f20e3c3c
	https://git.kernel.org/stable/c/3e4c56cf41876ef2a82f0877fe2a67648f8632b8
	https://git.kernel.org/stable/c/3c74b5787caf59bb1e9c5fe0a360643a71eb1e8a
	https://git.kernel.org/stable/c/071ed42cff4fcdd89025d966d48eabef59913bf2