net: bridge: mdb: restart port group walk after deletion

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 <fouriezhang@tencent.com>
Acked-by: Nikolay Aleksandrov <razor@blackwall.org>
Link: https://patch.msgid.link/20260920110852.60293-1-fouriezhang@tencent.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

0 files changed, 0 insertions, 0 deletions