CVE-2026-72254: netfilter: nft_fib: reject fib expression on the netdev egress hook

CVE-2026-72254: netfilter: nft_fib: reject fib expression on the netdev egress hook

[Greg Kroah-Hartman]

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

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

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

netfilter: nft_fib: reject fib expression on the netdev egress hook

A fib expression in a netdev egress base chain dereferences nft_in(pkt),
NULL on the transmit path, causing a NULL pointer dereference at eval.
nft_fib_validate() masks the hook with NF_INET_* values, but netdev hook
numbers are a separate enum that aliases them (NF_NETDEV_EGRESS ==
NF_INET_LOCAL_IN), so an egress chain passes validation and then faults.

Add nft_fib_netdev_validate() that limits each result/flag to the netdev
hook where the device it reads exists: the input-device cases (OIF,
OIFNAME, ADDRTYPE with F_IIF) to ingress, the output-device case (ADDRTYPE
with F_OIF) to egress, ADDRTYPE with no device flag to both. Also restrict
nft_fib_validate() to NFPROTO_IPV4/IPV6/INET so its NF_INET_* masks are
not applied to another family's hooks.

The Linux kernel CVE team has assigned CVE-2026-72254 to this issue.


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

	Issue introduced in 5.16 with commit 42df6e1d221dddc0f2acf2be37e68d553ad65f96 and fixed in 6.6.148 with commit 4fee43759b489559a491f7c95f9bfa7a1d0c7a10
	Issue introduced in 5.16 with commit 42df6e1d221dddc0f2acf2be37e68d553ad65f96 and fixed in 6.12.101 with commit 568931f26af4727a51e8521f72efbc78d3b82410
	Issue introduced in 5.16 with commit 42df6e1d221dddc0f2acf2be37e68d553ad65f96 and fixed in 6.18.42 with commit d01c913febead04a01a5f3a6374d1f45504dc523
	Issue introduced in 5.16 with commit 42df6e1d221dddc0f2acf2be37e68d553ad65f96 and fixed in 7.1.5 with commit f68305267ebda7e839b5e8f77e8d77535a3d5a0f
	Issue introduced in 5.16 with commit 42df6e1d221dddc0f2acf2be37e68d553ad65f96 and fixed in 7.2-rc2 with commit d07955dd34ecae17d35d8c7d0a273a3fba653a8c

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-2026-72254
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/netfilter/nft_fib.c
	net/netfilter/nft_fib_netdev.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/4fee43759b489559a491f7c95f9bfa7a1d0c7a10
	https://git.kernel.org/stable/c/568931f26af4727a51e8521f72efbc78d3b82410
	https://git.kernel.org/stable/c/d01c913febead04a01a5f3a6374d1f45504dc523
	https://git.kernel.org/stable/c/f68305267ebda7e839b5e8f77e8d77535a3d5a0f
	https://git.kernel.org/stable/c/d07955dd34ecae17d35d8c7d0a273a3fba653a8c