CVE-2026-98441: net/sched: act_ct: avoid modifying shared unconfirmed ct entry

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

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

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

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

net/sched: act_ct: avoid modifying shared unconfirmed ct entry

In a case where skb with an unconfirmed ct entry gets cloned, we may
end up processing both again but with different sets of extensions.

The series of events:

 1. The first clone wants to commit and runs the helpers wiring up
    the extension pointer into the expectation list.
 2. Then it looses the confirmation keeping the entry unconfirmed.
 3. Second clone now wants to commit labels or run NAT and adds the
    new extension for that breaking the pointer in the expectation
    list causing UAF on the destruction path later.

While this is possible to trigger, there should be no practical
network pipeline where we need to process both clones without
modifications in the same zone.  So, let's just reset the entry in
case for some reason we got an skb with a shared one.  This doesn't
affect any known use cases, but avoids any potential problems with
sharing and modification of the unconfirmed ct entry.

Unlike openvswitch module, act_ct allows for NAT without commit.
Changing that would be a uAPI break.  So, act_ct needs to reset on NAT
regardless of the commit flag to avoid reallocation of the extension
space.  This, however, doesn't really change the picture for sensible
networking cases as there should be no need to run the same packet
twice (before and after the clone) through conntrack without packet
header or zone changes and without commit.

The fixes tag points to the introduction of helpers, since that's the
main UAF trigger for the sharing.

The Linux kernel CVE team has assigned CVE-2026-98441 to this issue.


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

	Issue introduced in 6.2 with commit a21b06e7319129994f339ed47f512bbe57b77f5b and fixed in 6.12.112 with commit 2b783c562c3238ff50c34fd7a72a735c9cc73d9a
	Issue introduced in 6.2 with commit a21b06e7319129994f339ed47f512bbe57b77f5b and fixed in 6.18.55 with commit 4a04ed91575819fb1859311113e95700b709bec7
	Issue introduced in 6.2 with commit a21b06e7319129994f339ed47f512bbe57b77f5b and fixed in 7.2.9 with commit b097d9d7a5b09c8ec5c4c1a08e35ac5a66b06b44
	Issue introduced in 6.2 with commit a21b06e7319129994f339ed47f512bbe57b77f5b and fixed in 7.3-rc5 with commit f85009dfcd65e5969526b0db7a49b5413746e630

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-2026-98441
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/act_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/2b783c562c3238ff50c34fd7a72a735c9cc73d9a
	https://git.kernel.org/stable/c/4a04ed91575819fb1859311113e95700b709bec7
	https://git.kernel.org/stable/c/b097d9d7a5b09c8ec5c4c1a08e35ac5a66b06b44
	https://git.kernel.org/stable/c/f85009dfcd65e5969526b0db7a49b5413746e630