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

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Message-Id: <20180920.113113.1168948449098131783.davem@davemloft.net>
Date:   Thu, 20 Sep 2018 11:31:13 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     lucien.xin@...il.com
Cc:     netdev@...r.kernel.org, linux-sctp@...r.kernel.org,
        marcelo.leitner@...il.com, nhorman@...driver.com
Subject: Re: [PATCH net] sctp: update dst pmtu with the correct daddr

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?

Thanks.