CVE-2026-80996: net: l2tp: do not propagate multicast notification errors

CVE-2026-80996: net: l2tp: do not propagate multicast notification errors

[Greg Kroah-Hartman]

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

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

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

net: l2tp: do not propagate multicast notification errors

The tunnel create, tunnel modify, session create, and session modify
netlink handlers send multicast notifications through helpers that can fail
while allocating or encoding a message, or while multicasting it.

For tunnel and session create/modify, a notification is sent after the live
operation has completed. Returning a best-effort notification error as the
command result can therefore report failure for an operation that already
committed and can cause callers to retry and accumulate live objects.

Keep sending notifications for listener visibility, but do not propagate
their best-effort status as the command result. This also keeps the tunnel
modify command consistent with the other notification-only paths.

The Linux kernel CVE team has assigned CVE-2026-80996 to this issue.


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

	Issue introduced in 4.0 with commit 33f72e6f0c67f673fd0c63a8182dbd9ffb8cf50b and fixed in 6.12.109 with commit 0fe037d5eaad938aa3e9143ee071aa237750b42b
	Issue introduced in 4.0 with commit 33f72e6f0c67f673fd0c63a8182dbd9ffb8cf50b and fixed in 6.18.50 with commit 9c340473f4822bb31b151c19afd17448eda5acd1
	Issue introduced in 4.0 with commit 33f72e6f0c67f673fd0c63a8182dbd9ffb8cf50b and fixed in 7.2.4 with commit 50c4038f1670bf9a80c6a58ae83d1602decd8481
	Issue introduced in 4.0 with commit 33f72e6f0c67f673fd0c63a8182dbd9ffb8cf50b and fixed in 7.3-rc1 with commit af20e269f7459d2ce69887fdf2fad7caf986c865

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-2026-80996
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/l2tp/l2tp_netlink.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/0fe037d5eaad938aa3e9143ee071aa237750b42b
	https://git.kernel.org/stable/c/9c340473f4822bb31b151c19afd17448eda5acd1
	https://git.kernel.org/stable/c/50c4038f1670bf9a80c6a58ae83d1602decd8481
	https://git.kernel.org/stable/c/af20e269f7459d2ce69887fdf2fad7caf986c865