CVE-2026-53013: macvlan: fix macvlan_get_size() not reserving space for IFLA_MACVLAN_BC_CUTOFF

CVE-2026-53013: macvlan: fix macvlan_get_size() not reserving space for IFLA_MACVLAN_BC_CUTOFF

[Greg Kroah-Hartman]

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

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

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

macvlan: fix macvlan_get_size() not reserving space for IFLA_MACVLAN_BC_CUTOFF

macvlan_get_size() does not account for IFLA_MACVLAN_BC_CUTOFF, but
macvlan_fill_info() conditionally includes it when port->bc_cutoff != 1.
This causes nla_put_s32() to fail with -EMSGSIZE when the netlink skb
runs out of space, triggering a WARN_ON in rtnetlink and preventing the
interface from being dumped.

The bug can be reproduced with:

  ip link add macvlan0 link eth0 type macvlan mode bridge
  ip link set macvlan0 type macvlan bc_cutoff 0
  ip -d link show macvlan0   # fails with -EMSGSIZE

The bc_cutoff feature was added in commit 954d1fa1ac93 ("macvlan: Add
netlink attribute for broadcast cutoff"), which added the nla_put_s32()
call in macvlan_fill_info() but missed adding the corresponding
nla_total_size(4) in macvlan_get_size(). A follow-up commit
55cef78c244d ("macvlan: add forgotten nla_policy for
IFLA_MACVLAN_BC_CUTOFF") fixed the missing nla_policy entry but still
did not fix the size calculation.

The Linux kernel CVE team has assigned CVE-2026-53013 to this issue.


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

	Issue introduced in 6.4 with commit 954d1fa1ac93aa8a66f7d9a9ba545cf7f020d348 and fixed in 6.6.141 with commit 4979252758387b338ca968ba7e0515b0ae2257e3
	Issue introduced in 6.4 with commit 954d1fa1ac93aa8a66f7d9a9ba545cf7f020d348 and fixed in 6.12.91 with commit 77ecfa4e27f282d224215895ddfbeb916fc75e24
	Issue introduced in 6.4 with commit 954d1fa1ac93aa8a66f7d9a9ba545cf7f020d348 and fixed in 6.18.33 with commit b6b7154e9f5d75b608ceb2d05b376de8c638c40e
	Issue introduced in 6.4 with commit 954d1fa1ac93aa8a66f7d9a9ba545cf7f020d348 and fixed in 7.0.10 with commit 1c004f14ccdc11585625c168bb9a7c5e1b8afb0c
	Issue introduced in 6.4 with commit 954d1fa1ac93aa8a66f7d9a9ba545cf7f020d348 and fixed in 7.1 with commit fa92a77b0ed4d5f11a71665a232ac5a54a4b055d

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-2026-53013
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:
	drivers/net/macvlan.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/4979252758387b338ca968ba7e0515b0ae2257e3
	https://git.kernel.org/stable/c/77ecfa4e27f282d224215895ddfbeb916fc75e24
	https://git.kernel.org/stable/c/b6b7154e9f5d75b608ceb2d05b376de8c638c40e
	https://git.kernel.org/stable/c/1c004f14ccdc11585625c168bb9a7c5e1b8afb0c
	https://git.kernel.org/stable/c/fa92a77b0ed4d5f11a71665a232ac5a54a4b055d