From 8dca36978aa80bab9d4da130c211db75c9e00048 Mon Sep 17 00:00:00 2001 From: Nikolay Aleksandrov Date: Wed, 5 Nov 2025 13:19:18 +0200 Subject: net: bridge: fix use-after-free due to MST port state bypass syzbot reported[1] a use-after-free when deleting an expired fdb. It is due to a race condition between learning still happening and a port being deleted, after all its fdbs have been flushed. The port's state has been toggled to disabled so no learning should happen at that time, but if we have MST enabled, it will bypass the port's state, that together with VLAN filtering disabled can lead to fdb learning at a time when it shouldn't happen while the port is being deleted. VLAN filtering must be disabled because we flush the port VLANs when it's being deleted which will stop learning. This fix adds a check for the port's vlan group which is initialized to NULL when the port is getting deleted, that avoids the port state bypass. When MST is enabled there would be a minimal new overhead in the fast-path because the port's vlan group pointer is cache-hot. [1] https://syzkaller.appspot.com/bug?extid=dd280197f0f7ab3917be Fixes: ec7328b59176 ("net: bridge: mst: Multiple Spanning Tree (MST) mode") Reported-by: syzbot+dd280197f0f7ab3917be@syzkaller.appspotmail.com Closes: https://lore.kernel.org/netdev/69088ffa.050a0220.29fc44.003d.GAE@google.com/ Signed-off-by: Nikolay Aleksandrov Reviewed-by: Ido Schimmel Link: https://patch.msgid.link/20251105111919.1499702-2-razor@blackwall.org Signed-off-by: Jakub Kicinski --- net/bridge/br_forward.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'net/bridge/br_forward.c') diff --git a/net/bridge/br_forward.c b/net/bridge/br_forward.c index 870bdf2e082c..dea09096ad0f 100644 --- a/net/bridge/br_forward.c +++ b/net/bridge/br_forward.c @@ -25,7 +25,7 @@ static inline int should_deliver(const struct net_bridge_port *p, vg = nbp_vlan_group_rcu(p); return ((p->flags & BR_HAIRPIN_MODE) || skb->dev != p->dev) && - (br_mst_is_enabled(p->br) || p->state == BR_STATE_FORWARDING) && + (br_mst_is_enabled(p) || p->state == BR_STATE_FORWARDING) && br_allowed_egress(vg, skb) && nbp_switchdev_allowed_egress(p, skb) && !br_skb_isolated(p, skb); } -- cgit v1.2.3