linux-cve-announce - CVE-2025-68768: inet: frags: flush pending skbs in fqdir_pre

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Message-ID: <2026011356-CVE-2025-68768-d458@gregkh>
Date: Tue, 13 Jan 2026 16:28:54 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-68768: inet: frags: flush pending skbs in fqdir_pre_exit()

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

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

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

inet: frags: flush pending skbs in fqdir_pre_exit()

We have been seeing occasional deadlocks on pernet_ops_rwsem since
September in NIPA. The stuck task was usually modprobe (often loading
a driver like ipvlan), trying to take the lock as a Writer.
lockdep does not track readers for rwsems so the read wasn't obvious
from the reports.

On closer inspection the Reader holding the lock was conntrack looping
forever in nf_conntrack_cleanup_net_list(). Based on past experience
with occasional NIPA crashes I looked thru the tests which run before
the crash and noticed that the crash follows ip_defrag.sh. An immediate
red flag. Scouring thru (de)fragmentation queues reveals skbs sitting
around, holding conntrack references.

The problem is that since conntrack depends on nf_defrag_ipv6,
nf_defrag_ipv6 will load first. Since nf_defrag_ipv6 loads first its
netns exit hooks run _after_ conntrack's netns exit hook.

Flush all fragment queue SKBs during fqdir_pre_exit() to release
conntrack references before conntrack cleanup runs. Also flush
the queues in timer expiry handlers when they discover fqdir->dead
is set, in case packet sneaks in while we're running the pre_exit
flush.

The commit under Fixes is not exactly the culprit, but I think
previously the timer firing would eventually unblock the spinning
conntrack.

The Linux kernel CVE team has assigned CVE-2025-68768 to this issue.

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

	Issue introduced in 5.3 with commit d5dd88794a13c2f24cce31abad7a0a6c5e0ed2db and fixed in 6.18.3 with commit c70df25214ac9b32b53e18e6ae3b8f073ffa6903
	Issue introduced in 5.3 with commit d5dd88794a13c2f24cce31abad7a0a6c5e0ed2db and fixed in 6.19-rc2 with commit 006a5035b495dec008805df249f92c22c89c3d2e

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-2025-68768
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:
	include/net/inet_frag.h
	include/net/ipv6_frag.h
	net/ipv4/inet_fragment.c
	net/ipv4/ip_fragment.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/c70df25214ac9b32b53e18e6ae3b8f073ffa6903
	https://git.kernel.org/stable/c/006a5035b495dec008805df249f92c22c89c3d2e