From: Chinmay Agarwal chinagar@codeaurora.org
commit eb4e8fac00d1e01ada5e57c05d24739156086677 upstream.
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: 9c29a2f55ec0 ("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.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/core/neighbour.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)
--- a/net/core/neighbour.c +++ b/net/core/neighbour.c @@ -1244,13 +1244,14 @@ static int __neigh_update(struct neighbo old = neigh->nud_state; err = -EPERM;
- if (!(flags & NEIGH_UPDATE_F_ADMIN) && - (old & (NUD_NOARP | NUD_PERMANENT))) - goto out; if (neigh->dead) { NL_SET_ERR_MSG(extack, "Neighbor entry is now dead"); + new = old; goto out; } + if (!(flags & NEIGH_UPDATE_F_ADMIN) && + (old & (NUD_NOARP | NUD_PERMANENT))) + goto out;
ext_learn_change = neigh_update_ext_learned(neigh, flags, ¬ify);