Re: [PATCH net] udp: fix potential infinite loop in SO_REUSEPORT logic

[David Miller]

From: Eric Dumazet <eric.dumazet@xxxxxxxxx>
Date: Tue, 19 Jan 2016 08:36:43 -0800

> From: Eric Dumazet <edumazet@xxxxxxxxxx>
> 
> Using a combination of connected and un-connected sockets, Dmitry
> was able to trigger soft lockups with his fuzzer.
> 
> The problem is that sockets in the SO_REUSEPORT array might have
> different scores.
> 
> Right after sk2=socket(), setsockopt(sk2,...,SO_REUSEPORT, on) and
> bind(sk2, ...), but _before_ the connect(sk2) is done, sk2 is added into
> the soreuseport array, with a score which is smaller than the score of
> first socket sk1 found in hash table (I am speaking of the regular UDP
> hash table), if sk1 had the connect() done, giving a +8 to its score.
> 
> hash bucket [X] -> sk1 -> sk2 -> NULL
> 
> sk1 score = 14  (because it did a connect())
> sk2 score = 6
> 
> SO_REUSEPORT fast selection is an optimization. If it turns out the
> score of the selected socket does not match score of first socket, just
> fallback to old SO_REUSEPORT logic instead of trying to be too smart.
> 
> Normal SO_REUSEPORT users do not mix different kind of sockets, as this
> mechanism is used for load balance traffic.
> 
> Fixes: e32ea7e74727 ("soreuseport: fast reuseport UDP socket selection")
> Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
> Cc: Craig Gallek <kraigatgoog@xxxxxxxxx>

Applied, thanks Eric.