CVE-2026-74347: netfilter: cttimeout: detach dataplane timeout policy and repurpose refcount

From: Greg Kroah-Hartman <[email protected]>

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

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

netfilter: cttimeout: detach dataplane timeout policy and repurpose refcount

Add a refcount for struct nf_ct_timeout which is used by ct extension to
set the custom ct timeout policy, this tells us that the ct timeout is
being used by a conntrack entry. When the last conntrack entry drops the
refcount on the ct timeout, the ct timeout is released.

Remove the refcount for control plane which controls if the ruleset
refers to the timeout policy. After this update, it is possible to
remove the ct timeout policy from nfnetlink_cttimeout immediately.
This is for simplicity not to handle two refcounts on a single object.

Remove nf_queue_nf_hook_drop(): a packet sitting in nfqueue will just
hold a reference to the nf_ct_timeout object until packet is reinjected,
since this is part of the ct extension, this will be released by the
time the conntrack is freed.

nf_ct_untimeout() is still called to clean up in a best effort basis:
the ct timeout on existing entries gets removed when the ct timeout goes
away, but as long as the iptables ruleset still refers to the ct timeout
through a template, new conntracks may keep attaching it and extend its
lifetime until the rule is removed.

nf_ct_untimeout() is not called anymore from module removal path, this
is unlikely to find timeouts give module refcount is bumped, and the new
refcount already tracks the ct timeout policy use so it is released when
unused.

The Linux kernel CVE team has assigned CVE-2026-74347 to this issue.


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

	Issue introduced in 3.4 with commit 50978462300f74dc48aea4a38471cb69bdf741a5 and fixed in 7.1.5 with commit 9aeb0dcfeb460d33d61d434148b51103ab1d2013
	Issue introduced in 3.4 with commit 50978462300f74dc48aea4a38471cb69bdf741a5 and fixed in 7.2-rc1 with commit 7d6a9cdb8d3a51d9cfe546a09a518ab3d2671549

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-2026-74347
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/netfilter/nf_conntrack_timeout.h
	net/netfilter/nf_conntrack_core.c
	net/netfilter/nf_conntrack_timeout.c
	net/netfilter/nfnetlink_cttimeout.c
	net/netfilter/nft_ct.c
	net/netfilter/xt_CT.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/9aeb0dcfeb460d33d61d434148b51103ab1d2013
	https://git.kernel.org/stable/c/7d6a9cdb8d3a51d9cfe546a09a518ab3d2671549