netdev - Re: [PATCH] ipv4: Fix ip_skb_dst_mtu to use the sk passed by ip_finish

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Message-Id: <20160630.090315.592285556929128713.davem@davemloft.net>
Date:	Thu, 30 Jun 2016 09:03:15 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	shmulik.ladkani@...il.com
Cc:	hannes@...hat.com, tom@...bertland.com, azhou@....org,
	stephen@...workplumber.org, netdev@...r.kernel.org
Subject: Re: [PATCH] ipv4: Fix ip_skb_dst_mtu to use the sk passed by
 ip_finish_output

From: Shmulik Ladkani <shmulik.ladkani@...il.com>
Date: Wed, 29 Jun 2016 21:47:03 +0300

> ip_skb_dst_mtu uses skb->sk, assuming it is an AF_INET socket (e.g. it
> calls ip_sk_use_pmtu which casts sk as an inet_sk).
> 
> However, in the case of UDP tunneling, the skb->sk is not necessarily an
> inet socket (could be AF_PACKET socket, or AF_UNSPEC if arriving from
> tun/tap).
> 
> OTOH, the sk passed as an argument throughout IP stack's output path is
> the one which is of PMTU interest:
>  - In case of local sockets, sk is same as skb->sk;
>  - In case of a udp tunnel, sk is the tunneling socket.
> 
> Fix, by passing ip_finish_output's sk to ip_skb_dst_mtu.
> This augments 7026b1ddb6 'netfilter: Pass socket pointer down through okfn().'
> 
> Signed-off-by: Shmulik Ladkani <shmulik.ladkani@...il.com>

Applied, thanks.