6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Fourie Zhang commit ab1404ac81154a89fb61ac50ae9a04cd8d4834dc upstream. br_mdb_flush_pgs() keeps a pointer-to-pointer cursor while walking mp->ports. br_multicast_del_pg() can re-enter the same MDB entry through br_multicast_sg_del_exclude_ports() and unlink other port groups. If the cursor points into one of those groups, the next iteration dereferences a stale cursor and can leave mp->ports pointing at freed memory. A following RTM_GETMDB exposes the dangling pointer: BUG: KASAN: slab-use-after-free in br_mdb_dump Read of size 8 br_mdb_dump rtnl_mdb_dump rtnl_dumpit netlink_dump Reset the cursor to mp->ports after every deletion. The deletion removes at least the selected group, so the restarted walk always makes progress. Fixes: a6acb535afb2 ("bridge: mdb: Add MDB bulk deletion support") Cc: stable@vger.kernel.org Signed-off-by: Fourie Zhang Acked-by: Nikolay Aleksandrov Link: https://patch.msgid.link/20260920110852.60293-1-fouriezhang@tencent.com Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman --- net/bridge/br_mdb.c | 2 ++ 1 file changed, 2 insertions(+) --- a/net/bridge/br_mdb.c +++ b/net/bridge/br_mdb.c @@ -1523,6 +1523,8 @@ static void br_mdb_flush_pgs(struct net_ } br_multicast_del_pg(mp, p, pp); + /* br_multicast_del_pg() can remove other groups from this list. */ + pp = &mp->ports; } }