Subject: CVE-2024-27390: ipv6: mcast: remove one synchronize_net() barrier in ipv6_mc_down()

From: Greg Kroah-Hartman <[email-masked]>

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

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

ipv6: mcast: remove one synchronize_net() barrier in ipv6_mc_down()

As discussed in the past (commit 2d3916f31891 ("ipv6: fix skb drops
in igmp6_event_query() and igmp6_event_report()")) I think the
synchronize_net() call in ipv6_mc_down() is not needed.

Under load, synchronize_net() can last between 200 usec and 5 ms.

KASAN seems to agree as well.

The Linux kernel CVE team has assigned CVE-2024-27390 to this issue.

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

	Issue introduced in 5.13 with commit f185de28d9ae and fixed in 5.15.153 with commit 9d159d6637cc
	Issue introduced in 5.13 with commit f185de28d9ae and fixed in 6.1.83 with commit a03ede2282eb
	Issue introduced in 5.13 with commit f185de28d9ae and fixed in 6.6.23 with commit 26d4bac55750
	Issue introduced in 5.13 with commit f185de28d9ae and fixed in 6.7.11 with commit 7eb06ee59211
	Issue introduced in 5.13 with commit f185de28d9ae and fixed in 6.8.2 with commit 5da9a218340a
	Issue introduced in 5.13 with commit f185de28d9ae and fixed in 6.9 with commit 17ef8efc00b3

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-2024-27390
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/ipv6/mcast.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/9d159d6637ccce25f879d662a480541ef4ba3a50
	https://git.kernel.org/stable/c/a03ede2282ebbd181bd6f5c38cbfcb5765afcd04
	https://git.kernel.org/stable/c/26d4bac55750d535f1f0b8790dc26daf6089e373
	https://git.kernel.org/stable/c/7eb06ee5921189812e6b4bfe7b0f1e878be16df7
	https://git.kernel.org/stable/c/5da9a218340a2bc804dc4327e5804392e24a0b88
	https://git.kernel.org/stable/c/17ef8efc00b34918b966388b2af0993811895a8c