CVE-2026-64032

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>