CVE-2026-72451: xfrm: Fix xfrm state cache insertion race

CVE-2026-72451: xfrm: Fix xfrm state cache insertion race

[Greg Kroah-Hartman]

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

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

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

xfrm: Fix xfrm state cache insertion race

The xfrm input state cache insertion code checks the validity of
the state before acquiring the global xfrm_state_lock.  Thus it's
possible for someone else to kill the state after it passed the
validity check, and then the insertion will add the dead state
to the cache.

Fix this by moving the validity check inside the lock.

This entire function is called on the input path, where BH must
be off (e.g., the caller of this function xfrm_input acquires
its spinlocks without disabling BH).

So there is no need to disable BH here or take the RCU read lock.
Remove both and replace them with an assertion that trips if BH
is accidentally enabled on some future calling path.

The Linux kernel CVE team has assigned CVE-2026-72451 to this issue.


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

	Issue introduced in 6.12.13 with commit 5e4334dc39443645415450163ff5ff1ee7e79784 and fixed in 6.12.97 with commit 6dab4dec9a49121d079981ac913569f232c06b06
	Issue introduced in 6.13 with commit 81a331a0e72ddc2f75092603d9577bd1a0ca23ad and fixed in 6.18.40 with commit a1a3360a0c44b8b5c134db2a9d0667b61c9cf523
	Issue introduced in 6.13 with commit 81a331a0e72ddc2f75092603d9577bd1a0ca23ad and fixed in 7.1.5 with commit 041859fd55c81ea55e76d051e39b7b79975b8c7d
	Issue introduced in 6.13 with commit 81a331a0e72ddc2f75092603d9577bd1a0ca23ad and fixed in 7.2-rc1 with commit ddd3d0132920319ac426e12456013eadbae67e15

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-2026-72451
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/xfrm/xfrm_state.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/6dab4dec9a49121d079981ac913569f232c06b06
	https://git.kernel.org/stable/c/a1a3360a0c44b8b5c134db2a9d0667b61c9cf523
	https://git.kernel.org/stable/c/041859fd55c81ea55e76d051e39b7b79975b8c7d
	https://git.kernel.org/stable/c/ddd3d0132920319ac426e12456013eadbae67e15