neighbour: Prevent a dead entry from updating gc_list
Following race condition was detected: <CPU A, t0> - neigh_flush_dev() is under execution and calls neigh_mark_dead(n) marking the neighbour entry 'n' as dead. <CPU B, t1> - Executing: __netif_receive_skb() -> __netif_receive_skb_core() -> arp_rcv() -> arp_process().arp_process() calls __neigh_lookup() which takes a reference on neighbour entry 'n'. <CPU A, t2> - Moves further along neigh_flush_dev() and calls neigh_cleanup_and_release(n), but since reference count increased in t2, 'n' couldn't be destroyed. <CPU B, t3> - Moves further along, arp_process() and calls neigh_update()-> __neigh_update() -> neigh_update_gc_list(), which adds the neighbour entry back in gc_list(neigh_mark_dead(), removed it earlier in t0 from gc_list) <CPU B, t4> - arp_process() finally calls neigh_release(n), destroying the neighbour entry. This leads to 'n' still being part of gc_list, but the actual neighbour structure has been freed. The situation can be prevented from happening if we disallow a dead entry to have any possibility of updating gc_list. This is what the patch intends to achieve. Fixes: 9c29a2f5 ("neighbor: Fix locking order for gc_list changes") Signed-off-by: Chinmay Agarwal <chinagar@codeaurora.org> Reviewed-by: Cong Wang <xiyou.wangcong@gmail.com> Reviewed-by: David Ahern <dsahern@kernel.org> Link: https://lore.kernel.org/r/20210127165453.GA20514@chinagar-linux.qualcomm.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>
Showing
Please register or sign in to comment