netdev - Re: [PATCH net] sctp: update dst pmtu with the correct daddr

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Message-ID: <CADvbK_djerrPki_weXxxwpf3ncT=k2PxK2=gB0BUKToznBRyCA@mail.gmail.com>
Date:   Fri, 21 Sep 2018 15:55:34 +0800
From:   Xin Long <lucien.xin@...il.com>
To:     davem <davem@...emloft.net>
Cc:     network dev <netdev@...r.kernel.org>, linux-sctp@...r.kernel.org,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        Neil Horman <nhorman@...driver.com>
Subject: Re: [PATCH net] sctp: update dst pmtu with the correct daddr

On Fri, Sep 21, 2018 at 2:31 AM David Miller <davem@...emloft.net> wrote:
>
> From: Xin Long <lucien.xin@...il.com>
> Date: Thu, 20 Sep 2018 17:27:28 +0800
>
> > When processing pmtu update from an icmp packet, it calls .update_pmtu
> > with sk instead of skb in sctp_transport_update_pmtu.
> >
> > However for sctp, the daddr in the transport might be different from
> > inet_sock->inet_daddr or sk->sk_v6_daddr, which is used to update or
> > create the route cache. The incorrect daddr will cause a different
> > route cache created for the path.
> >
> > So before calling .update_pmtu, inet_sock->inet_daddr/sk->sk_v6_daddr
> > should be updated with the daddr in the transport, and update it back
> > after it's done.
> >
> > The issue has existed since route exceptions introduction.
> >
> > Fixes: 4895c771c7f0 ("ipv4: Add FIB nexthop exceptions.")
> > Reported-by: ian.periam@...logic.com
> > Signed-off-by: Xin Long <lucien.xin@...il.com>
>
> Applied and queued up for -stable.
>
> Although are you sure it's OK to temporarily change the sockets address
> like this?  What if an asynchronous context looks at the socket state
> and sees the temporarily set address?
It's under the protection of the sock lock, I think any other places that
want to access the address also need to acquire this sock lock first.