Commit 5a3f7a683aee for kernel

commit 5a3f7a683aee56e1f15c9d53041f3236767eaae7
Author: Jun Yang <littleddfu@gmail.com>
Date:   Mon Aug 31 19:13:04 2026 +0800

    net: bridge: mcast: don't truncate the port group walk on teardown

    __br_multicast_disable_port_ctx() and br_multicast_del_port() walk
    port->mglist with hlist_for_each_entry_safe(). However,
    br_multicast_find_del_pg() can also delete other entries from the same
    list through br_multicast_fwd_src_remove() or __fwd_del_star_excl().

    If such an entry is the iterator's saved next node, hlist_del_init()
    clears its ->next and terminates the walk early. The reproducer triggers
    this in both teardown walks, leaving port groups in the bridge mdb with
    a dangling ->key.port after del_nbp() frees the port:

      BUG: KASAN: slab-use-after-free in __mdb_fill_info+0x1191/0x1320
       __mdb_fill_info+0x1191/0x1320
       br_mdb_dump+0x594/0xe40
       rtnl_mdb_dump+0x1cf/0x5d0

    Use hlist_del_init_rcu() to unlink the group while preserving ->next.
    br_multicast_del_pg() and the teardown walks run under
    br->multicast_lock. The GC worker must acquire the same lock before
    detaching the group for destruction, so the node remains alive while
    the walk uses the preserved pointer.

    Preserving ->next means a walk can now reach a group that an earlier
    iteration already deleted as a side effect. That group is off mp->ports,
    so br_multicast_find_del_pg() would fall through its port scan and hit
    the trailing WARN_ON(1). Skip such groups at the top of that helper: a
    port group is put on port->mglist when it is created and only unlinked
    when it is deleted, so hlist_unhashed() identifies exactly this case.

    Fixes: b08123684bd5 ("net: bridge: mcast: install S,G entries automatically based on reports")
    Cc: stable@vger.kernel.org
    Suggested-by: Nikolay Aleksandrov <razor@blackwall.org>
    Reported-by: TencentOS Corvus AI <corvus@tencent.com>
    Signed-off-by: Jun Yang <junvyyang@tencent.com>
    Reviewed-by: Nikolay Aleksandrov <razor@blackwall.org>
    Link: https://patch.msgid.link/20260831111330.199543-1-junvyyang@tencent.com
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
index 3ef5d8bbf552..3e9b10f8abf1 100644
--- a/net/bridge/br_multicast.c
+++ b/net/bridge/br_multicast.c
@@ -808,7 +808,11 @@ void br_multicast_del_pg(struct net_bridge_mdb_entry *mp,
 	struct hlist_node *tmp;

 	rcu_assign_pointer(*pp, pg->next);
-	hlist_del_init(&pg->mglist);
+	/* Keep ->next (held under multicast_lock, freed later by the GC work):
+	 * a port->mglist teardown walk may have latched this node as its next,
+	 * and deleting other groups of the same port must not truncate it.
+	 */
+	hlist_del_init_rcu(&pg->mglist);
 	br_multicast_eht_clean_sets(pg);
 	hlist_for_each_entry_safe(ent, tmp, &pg->src_list, node)
 		br_multicast_del_group_src(ent, false);
@@ -835,6 +839,13 @@ static void br_multicast_find_del_pg(struct net_bridge *br,
 	struct net_bridge_mdb_entry *mp;
 	struct net_bridge_port_group *p;

+	/* A teardown walk over port->mglist can reach a group that an earlier
+	 * iteration already deleted as a side effect. It is off mp->ports by
+	 * now, so skip it instead of falling through to the WARN_ON() below.
+	 */
+	if (hlist_unhashed(&pg->mglist))
+		return;
+
 	mp = br_mdb_ip_get(br, &pg->key.addr);
 	if (WARN_ON(!mp))
 		return;