CVE-2026-89950: batman-adv: mcast: linearize skbuff for packet generation

CVE-2026-89950: batman-adv: mcast: linearize skbuff for packet generation

[Greg Kroah-Hartman]

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

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

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

batman-adv: mcast: linearize skbuff for packet generation

batadv_mcast_forw_packet() and batadv_mcast_forw_scrape() is not only
called (indirectly) by the unsharing+linearizing batadv_recv_mcast_packet()
handler. When it is called (indirectly) by batadv_mcast_forw_mcsend() then
it will be unshared but not linearized. The SKB_LINEAR_ASSERT() can
therefore cause a fatal BUG().

The linearization should happen during the expansion of the head because
the scrape function can be hit already during the initial
batadv_mcast_forw_mode() selection code:

* batadv_interface_tx
* batadv_mcast_forw_mode
* batadv_mcast_forw_mode_by_count()
* batadv_mcast_forw_push()
  -> calls batadv_mcast_forw_expand_head() before everything else
* batadv_mcast_forw_push_tvlvs()
* batadv_mcast_forw_push_dests()
* batadv_mcast_forw_push_adjust_padding()
* batadv_mcast_forw_scrape()

The Linux kernel CVE team has assigned CVE-2026-89950 to this issue.


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

	Issue introduced in 6.8 with commit 90039133221e33964ccb4a536dad7eb0a372fff7 and fixed in 6.12.110 with commit a9603e0a7cb5e0cddc6b23af153cf7daafc5c55e
	Issue introduced in 6.8 with commit 90039133221e33964ccb4a536dad7eb0a372fff7 and fixed in 6.18.51 with commit c32e5e25c41201c8c3b796a4ab2c45103187091e
	Issue introduced in 6.8 with commit 90039133221e33964ccb4a536dad7eb0a372fff7 and fixed in 7.2.5 with commit 2879177539e3ece483a8e5406970373698e9a6c5
	Issue introduced in 6.8 with commit 90039133221e33964ccb4a536dad7eb0a372fff7 and fixed in 7.3-rc1 with commit 6a30a59e2660afd03c975f1b8eae6a2301161197

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-2026-89950
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/batman-adv/multicast_forw.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/a9603e0a7cb5e0cddc6b23af153cf7daafc5c55e
	https://git.kernel.org/stable/c/c32e5e25c41201c8c3b796a4ab2c45103187091e
	https://git.kernel.org/stable/c/2879177539e3ece483a8e5406970373698e9a6c5
	https://git.kernel.org/stable/c/6a30a59e2660afd03c975f1b8eae6a2301161197