__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: [email protected]
Suggested-by: Nikolay Aleksandrov <[email protected]>
Reported-by: TencentOS Corvus AI <[email protected]>
Assisted-by: tencentos-corvus-ai:kimi-k3
Signed-off-by: Jun Yang <[email protected]>
---
v3: skip already-unlinked groups at the top of br_multicast_find_del_pg()
instead of in each teardown walk, per Nikolay's suggestion, so the
preserved ->next no longer leads to the trailing WARN_ON(1).
v2: https://lore.kernel.org/netdev/[email protected]/
Use hlist_del_init_rcu() to preserve ->next, as suggested by Nikolay,
instead of restarting the walks.
v1: https://lore.kernel.org/all/[email protected]/
net/bridge/br_multicast.c | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)
diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
index 00aa9b2879d6..ea0a50eb8b77 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;
--
2.43.7
