Re: [PATCH RFC net] neigh: do not modify unlinked entries

[David Miller <davem@davemloft.net>]

From: Julian Anastasov <ja@ssi.bg>
Date: Tue, 16 Jun 2015 22:56:39 +0300

> The lockless lookups can return entry that is unlinked.
> Sometimes they get reference before last neigh_cleanup_and_release,
> sometimes they do not need reference. Later, any
> modification attempts may result in the following problems:
> 
> 1. entry is not destroyed immediately because neigh_update
> can start the timer for dead entry, eg. on change to NUD_REACHABLE
> state. As result, entry lives for some time but is invisible
> and out of control.
> 
> 2. __neigh_event_send can run in parallel with neigh_destroy
> while refcnt=0 but if timer is started and expired refcnt can
> reach 0 for second time leading to second neigh_destroy and
> possible crash.
> 
> Thanks to Eric Dumazet and Ying Xue for their work and analyze
> on the __neigh_event_send change.
> 
> Fixes: 767e97e1e0db ("neigh: RCU conversion of struct neighbour")
> Fixes: a263b3093641 ("ipv4: Make neigh lookups directly in output packet path.")
> Fixes: 6fd6ce2056de ("ipv6: Do not depend on rt->n in ip6_finish_output2().")
> Cc: Eric Dumazet <eric.dumazet@gmail.com>
> Cc: Ying Xue <ying.xue@windriver.com>
> Signed-off-by: Julian Anastasov <ja@ssi.bg>

Applied and queued up for -stable, thanks!