CVE-2026-72248: netfilter: flowtable: support IPIP tunnel with direct xmit

CVE-2026-72248: netfilter: flowtable: support IPIP tunnel with direct xmit

[Greg Kroah-Hartman]

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

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

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

netfilter: flowtable: support IPIP tunnel with direct xmit

The combination of IPIP tunnel with direct xmit, eg. bridge device,
breaks because no dst_entry is provided to check the skb headroom and to
set the iph->frag_off field. This leads to invalid dst usage and can
trigger a crash in the tunnel transmit path.

Fix this by moving dst_cache and dst_cookie out of the runtime union so
that they can be shared by neighbour, xfrm, and direct tunnel flows.
For FLOW_OFFLOAD_XMIT_DIRECT tuples carrying tunnel metadata, preserve
route state in these shared fields and release it through the common
dst release path.

Since dst_entry is now available to the three supported xmit modes and
dst_release() already deals with NULL dst, remove the xmit type check
in nft_flow_dst_release(). Moreover, skip the check if the dst entry
is NULL in nf_flow_dst_check() which is now the case for the direct
xmit case.

Based on patch from Rein Wei <n05ec@lzu.edu.cn>.

The Linux kernel CVE team has assigned CVE-2026-72248 to this issue.


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

	Issue introduced in 6.19 with commit d30301ba4b07ac92eb38353a111833b009003170 and fixed in 7.1.5 with commit 0880c4ed122d0cddc9f29a2b28f055d1f24f0fca
	Issue introduced in 6.19 with commit d30301ba4b07ac92eb38353a111833b009003170 and fixed in 7.2-rc3 with commit fa7395c02d95e51bad2952325d2d6503bfbad437

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-2026-72248
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_flow_table.h
	net/netfilter/nf_flow_table_core.c
	net/netfilter/nf_flow_table_ip.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/0880c4ed122d0cddc9f29a2b28f055d1f24f0fca
	https://git.kernel.org/stable/c/fa7395c02d95e51bad2952325d2d6503bfbad437