CVE-2026-64032: bridge: mcast: Fix a possible use-after-free when removing a bridge port

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

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

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

bridge: mcast: Fix a possible use-after-free when removing a bridge port

When per-VLAN multicast snooping is enabled, the bridge iterates over
all the bridge ports, disables the per-port multicast context on each
port and enables the per-{port, VLAN} multicast contexts instead. The
reverse happens when per-VLAN multicast snooping is disabled.

When global multicast snooping is enabled, the bridge iterates over all
the bridge ports and enables the per-port multicast context on each
port. The reverse happens when multicast snooping is disabled.

The above scheme can result in a situation where both types of contexts
(per-port and per-{port, VLAN}) are enabled on a single bridge port:

 # ip link add name br1 up type bridge mcast_snooping 1 mcast_querier 1 vlan_filtering 1
 # ip link add name dummy1 up master br1 type dummy
 # ip link set dev br1 type bridge mcast_vlan_snooping 1
 # ip link set dev br1 type bridge mcast_snooping 0
 # ip link set dev br1 type bridge mcast_snooping 1

This is not intended and it is a problem since the commit cited below.
Prior to this commit, when removing a bridge port,
br_multicast_disable_port() would disable the per-port multicast context
and the per-{port, VLAN} multicast contexts would get disabled when
flushing VLANs.

After this commit, br_multicast_disable_port() only disables the
per-port multicast context if per-VLAN multicast snooping is disabled.
If both types of contexts were enabled on the port when it was removed,
the per-port multicast context would remain enabled when freeing the
bridge port, leading to a use-after-free [1].

Fix by preventing the bridge from enabling / disabling the per-port
multicast contexts when toggling global multicast snooping if per-VLAN
multicast snooping is enabled.

[1]
ODEBUG: free active (active state 0) object: ffff88810f8bda78 object type: timer_list hint: br_ip6_multicast_port_query_expired (net/bridge/br_multicast.c:1927)
WARNING: lib/debugobjects.c:629 at debug_print_object+0x1b1/0x3e0, CPU#5: swapper/5/0
[...]
Call Trace:
<IRQ>
__debug_check_no_obj_freed (lib/debugobjects.c:1116)
kfree (mm/slub.c:2620 mm/slub.c:6250 mm/slub.c:6565)
kobject_cleanup (lib/kobject.c:689)
rcu_do_batch (kernel/rcu/tree.c:2617)
rcu_core (kernel/rcu/tree.c:2869)
handle_softirqs (kernel/softirq.c:622)
__irq_exit_rcu (kernel/softirq.c:656 kernel/softirq.c:496 kernel/softirq.c:735)
irq_exit_rcu (kernel/softirq.c:752)
sysvec_apic_timer_interrupt (arch/x86/kernel/apic/apic.c:1061 (discriminator 47) arch/x86/kernel/apic/apic.c:1061 (discriminator 47))
</IRQ>

The Linux kernel CVE team has assigned CVE-2026-64032 to this issue.


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

	Issue introduced in 5.15.186 with commit 410a033bfa8c7daefbae0225c836693db2149ec1 and fixed in 5.15.209 with commit ddefd1b8e5eb58933a697ab38334f0fd82e7fb8b
	Issue introduced in 6.1.142 with commit c6d16eab122744df698f18b47cf771945cd55066 and fixed in 6.1.175 with commit ed3b69e60385a03df11c6d12e5d7bdf0f4a11b70
	Issue introduced in 6.6.95 with commit b4c83b37490d61cfdd62a2b29e98a9b89004b5c0 and fixed in 6.6.142 with commit 1900ca8acb92fbea8bf9abef9927c7fed03db7fc
	Issue introduced in 6.12.35 with commit 78f768e36c065ca3f88272fcf39014782c2d4ecd and fixed in 6.12.92 with commit ebe5561154c823b323bd06e350b55e0b8604d851
	Issue introduced in 6.16 with commit 4b30ae9adb047dd0a7982975ec3933c529537026 and fixed in 6.18.34 with commit a9224862d597d0eed0a34bbb27343f703fc4113f
	Issue introduced in 6.16 with commit 4b30ae9adb047dd0a7982975ec3933c529537026 and fixed in 7.0.11 with commit 7213256c91ed778a0997c2029c152b18dc50e4fd
	Issue introduced in 6.16 with commit 4b30ae9adb047dd0a7982975ec3933c529537026 and fixed in 7.1 with commit 4df78ff02629c7729168f0696a7a2123c389818d
	Issue introduced in 6.15.4 with commit c996e25df0b3282c724bb5aca434518bc08cd963

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-2026-64032
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/bridge/br_multicast.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/ddefd1b8e5eb58933a697ab38334f0fd82e7fb8b
	https://git.kernel.org/stable/c/ed3b69e60385a03df11c6d12e5d7bdf0f4a11b70
	https://git.kernel.org/stable/c/1900ca8acb92fbea8bf9abef9927c7fed03db7fc
	https://git.kernel.org/stable/c/ebe5561154c823b323bd06e350b55e0b8604d851
	https://git.kernel.org/stable/c/a9224862d597d0eed0a34bbb27343f703fc4113f
	https://git.kernel.org/stable/c/7213256c91ed778a0997c2029c152b18dc50e4fd
	https://git.kernel.org/stable/c/4df78ff02629c7729168f0696a7a2123c389818d