CVE-2026-97939: ipmr: account multicast table and route memory

CVE-2026-97939: ipmr: account multicast table and route memory

[Greg Kroah-Hartman]

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

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

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

ipmr: account multicast table and route memory

A netadmin in a user+net namespace can create many IPv4 and IPv6
multicast routing tables with MRT_TABLE and MRT6_TABLE. Each unseen
id allocates an mr_table via the shared mr_table_alloc(), links it
into the per-net list, and leaves it until netns teardown. Those
objects were not charged to memcg, so the host unreclaimable slab
grows with the table count.

Account mr_table allocations with GFP_KERNEL_ACCOUNT and mark the
IPv4/IPv6 MFC caches SLAB_ACCOUNT. This matches the established
handling of IP addresses, routes and alternate interface names.

Unresolved MFC entries are still allocated from softIRQ with
GFP_ATOMIC and are not charged. They expire after 10 seconds and are
bounded by the socket receive queue; see commit 0079ad8e8dc3
("ipmr: remove hard code cache_resolve_queue_len limit").

The Linux kernel CVE team has assigned CVE-2026-97939 to this issue.


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

	Issue introduced in 2.6.35 with commit f0ad0860d01e47a3ffd220564c5c653b3afbe962 and fixed in 6.18.53 with commit 0264b3ee09b118fec8a5471b4ca288f8ab84722f
	Issue introduced in 2.6.35 with commit f0ad0860d01e47a3ffd220564c5c653b3afbe962 and fixed in 7.2.7 with commit d0a2e2a4ee6bfe51e398bfb6921a7d0f4c26bc1c
	Issue introduced in 2.6.35 with commit f0ad0860d01e47a3ffd220564c5c653b3afbe962 and fixed in 7.3-rc3 with commit b7ee18725f2292ab554aa96a101ae42d45f008bd

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-2026-97939
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/ipv4/ipmr.c
	net/ipv4/ipmr_base.c
	net/ipv6/ip6mr.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/0264b3ee09b118fec8a5471b4ca288f8ab84722f
	https://git.kernel.org/stable/c/d0a2e2a4ee6bfe51e398bfb6921a7d0f4c26bc1c
	https://git.kernel.org/stable/c/b7ee18725f2292ab554aa96a101ae42d45f008bd