From 4df78ff02629c7729168f0696a7a2123c389818d Mon Sep 17 00:00:00 2001 From: Ido Schimmel Date: Sun, 17 May 2026 15:11:21 +0300 Subject: [PATCH] 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: __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)) Fixes: 4b30ae9adb04 ("net: bridge: mcast: re-implement br_multicast_{enable, disable}_port functions") Reported-by: syzbot+ae231e0552fa77b26ea1@syzkaller.appspotmail.com Closes: https://lore.kernel.org/netdev/87qznowlfs.ffs@tglx/ Reported-by: Thomas Gleixner Acked-by: Nikolay Aleksandrov Signed-off-by: Ido Schimmel Link: https://patch.msgid.link/20260517121122.188333-2-idosch@nvidia.com Signed-off-by: Jakub Kicinski --- net/bridge/br_multicast.c | 22 +++++++++++++++++----- 1 file changed, 17 insertions(+), 5 deletions(-) diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c index 881d866d687a..2eef4f3345cd 100644 --- a/net/bridge/br_multicast.c +++ b/net/bridge/br_multicast.c @@ -4640,10 +4640,24 @@ static void br_multicast_start_querier(struct net_bridge_mcast *brmctx, rcu_read_unlock(); } -static void br_multicast_del_grps(struct net_bridge *br) +static void br_multicast_enable_all_ports(struct net_bridge *br) { struct net_bridge_port *port; + if (br_opt_get(br, BROPT_MCAST_VLAN_SNOOPING_ENABLED)) + return; + + list_for_each_entry(port, &br->port_list, list) + __br_multicast_enable_port_ctx(&port->multicast_ctx); +} + +static void br_multicast_disable_all_ports(struct net_bridge *br) +{ + struct net_bridge_port *port; + + if (br_opt_get(br, BROPT_MCAST_VLAN_SNOOPING_ENABLED)) + return; + list_for_each_entry(port, &br->port_list, list) __br_multicast_disable_port_ctx(&port->multicast_ctx); } @@ -4651,7 +4665,6 @@ static void br_multicast_del_grps(struct net_bridge *br) int br_multicast_toggle(struct net_bridge *br, unsigned long val, struct netlink_ext_ack *extack) { - struct net_bridge_port *port; bool change_snoopers = false; int err = 0; @@ -4668,7 +4681,7 @@ int br_multicast_toggle(struct net_bridge *br, unsigned long val, br_opt_toggle(br, BROPT_MULTICAST_ENABLED, !!val); if (!br_opt_get(br, BROPT_MULTICAST_ENABLED)) { change_snoopers = true; - br_multicast_del_grps(br); + br_multicast_disable_all_ports(br); goto unlock; } @@ -4676,8 +4689,7 @@ int br_multicast_toggle(struct net_bridge *br, unsigned long val, goto unlock; br_multicast_open(br); - list_for_each_entry(port, &br->port_list, list) - __br_multicast_enable_port_ctx(&port->multicast_ctx); + br_multicast_enable_all_ports(br); change_snoopers = true;