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Date:   Wed, 2 Dec 2020 17:12:51 -0700
From:   David Ahern <dsahern@...il.com>
To:     Preethi Ramachandra <preethir@...iper.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Cc:     Jimmy Jose <jimmyj@...iper.net>,
        Reji Thomas <rejithomas@...iper.net>,
        Yogesh Ankolekar <ayogesh@...iper.net>
Subject: Re: Linux IPV6 TCP egress path device passed for LOCAL_OUT hook is
 incorrect

On 12/2/20 4:31 AM, Preethi Ramachandra wrote:
> Hi David Ahren,
> 
> In TCP egress path for ipv6 the device passed to NF_INET_LOCAL_OUT hook should be skb_dst(skb)->dev instead of dst->dev.
> 
> https://elixir.bootlin.com/linux/latest/source/net/ipv6/ip6_output.c#L202
> struct dst_entry *dst = skb_dst(skb); >>> This may return slave device.
> 
> In this code path the DST Dev and SKB DST Dev will be set to VRF master device.
> ip6_xmit->l3mdev_ip6_out->vrf_l3_out->vrf_ip6_out (This will set SKB DST Dev to vrf0)
> 
> However, once the control passes back to ip6_xmit, https://elixir.bootlin.com/linux/latest/source/net/ipv6/ip6_output.c#L280
> Slave device is passed to LOCAL_OUT nf_hook instead of skb_dst(skb)->dev.
> 
> return NF_HOOK(NFPROTO_IPV6, NF_INET_LOCAL_OUT,
>        net, (struct sock *)sk, skb, NULL, dst->dev, <<<< Should be skb_dst(skb)->dev
>        dst_output);

The vrf device version of that call is managed by the vrf driver. See
vrf_ip6_out_direct():

       err = nf_hook(NFPROTO_IPV6, NF_INET_LOCAL_OUT, net, sk,
                      skb, NULL, vrf_dev, vrf_ip6_out_direct_finish);

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