Re: [PATCH net] sctp: set flow sport from saddr only when it's 0

[David Miller <davem@davemloft.net>]

From: Xin Long <lucien.xin@gmail.com>
Date: Tue, 22 Jan 2019 02:42:41 +0800

> Now sctp_transport_pmtu() passes transport->saddr into .get_dst() to set
> flow sport from 'saddr'. However, transport->saddr is set only when
> transport->dst exists in sctp_transport_route().
> 
> If sctp_transport_pmtu() is called without transport->saddr set, like
> when transport->dst doesn't exists, the flow sport will be set to 0
> from transport->saddr, which will cause a wrong route to be got.
> 
> Commit 6e91b578bf3f ("sctp: re-use sctp_transport_pmtu in
> sctp_transport_route") made the issue be triggered more easily
> since sctp_transport_pmtu() would be called in sctp_transport_route()
> after that.
> 
> In gerneral, fl4->fl4_sport should always be set to
> htons(asoc->base.bind_addr.port), unless transport->asoc doesn't exist
> in sctp_v4/6_get_dst(), which is the case:
> 
>   sctp_ootb_pkt_new() ->
>     sctp_transport_route()
> 
> For that, we can simply handle it by setting flow sport from saddr only
> when it's 0 in sctp_v4/6_get_dst().
> 
> Fixes: 6e91b578bf3f ("sctp: re-use sctp_transport_pmtu in sctp_transport_route")
> Reported-by: Ying Xu <yinxu@redhat.com>
> Signed-off-by: Xin Long <lucien.xin@gmail.com>

Applied and queued up for -stable.