From 4b772869a1e5f9da5cef5b9c722ec0aa424ee0a0 Mon Sep 17 00:00:00 2001 From: Nikolay Aleksandrov Date: Thu, 3 Sep 2026 12:38:51 +0300 Subject: [PATCH] net: bridge: mcast: properly convert mglist to rcu Sashiko reported a bug [1] that br_multicast_del_port_group unlists the port group not using proper rcu helper that preserves the next pointer and after that immediately frees the port group without waiting for rcu grace period. The only rcu walker of mglist is br_multicast_list_adjacent() and it turns out that function has always been buggy because mglist was never properly converted to RCU. Fix it by converting it to rcu and moving its initialization after eth_addr's. Initializing p->next can use RCU_INIT_POINTER because we have a barrier from the hlist_add_head_rcu call later, besides we're initializing an unpublished structure anyway. [1] https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260826014200.362304-1-littleddfu%40gmail.com Fixes: 07f8ac4a1e26 ("bridge: add export of multicast database adjacent to net_dev") Signed-off-by: Nikolay Aleksandrov Reviewed-by: Ido Schimmel Link: https://patch.msgid.link/20260903093851.1494297-1-razor@blackwall.org Signed-off-by: Jakub Kicinski --- net/bridge/br_multicast.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c index 3e9b10f8abf1..2f9bb30e1a1f 100644 --- a/net/bridge/br_multicast.c +++ b/net/bridge/br_multicast.c @@ -1441,16 +1441,17 @@ struct net_bridge_port_group *br_multicast_new_port_group( goto free_out; } - rcu_assign_pointer(p->next, next); timer_setup(&p->timer, br_multicast_port_group_expired, 0); timer_setup(&p->rexmit_timer, br_multicast_port_group_rexmit, 0); - hlist_add_head(&p->mglist, &port->mglist); if (src) memcpy(p->eth_addr, src, ETH_ALEN); else eth_broadcast_addr(p->eth_addr); + RCU_INIT_POINTER(p->next, next); + hlist_add_head_rcu(&p->mglist, &port->mglist); + return p; free_out: @@ -1465,11 +1466,11 @@ void br_multicast_del_port_group(struct net_bridge_port_group *p) struct net_bridge_port *port = p->key.port; __u16 vid = p->key.addr.vid; - hlist_del_init(&p->mglist); + hlist_del_init_rcu(&p->mglist); if (!br_multicast_is_star_g(&p->key.addr)) rhashtable_remove_fast(&port->br->sg_port_tbl, &p->rhnode, br_sg_port_rht_params); - kfree(p); + kfree_rcu(p, rcu); br_multicast_port_ngroups_dec(port, vid); }