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

[Craig Gallek <kraigatgoog@gmail.com>]

On Tue, Jan 19, 2016 at 11:36 AM, Eric Dumazet <eric.dumazet@gmail.com> wrote:
> From: Eric Dumazet <edumazet@google.com>
>
> 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@google.com>
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Cc: Craig Gallek <kraigatgoog@gmail.com>

Thanks Eric!

Acked-by: Craig Gallek <kraig@google.com>