netdev - Re: Linux IPV6 TCP egress path device passed for LOCAL

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Date:   Thu, 3 Dec 2020 09:56:14 +0000
From:   Preethi Ramachandra <preethir@...iper.net>
To:     David Ahern <dsahern@...il.com>,
        "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

Thanks David for the response.
Our local kernel doesn’t have vrf_ip6_out_direct patch. I will pick this change from upstream to fix the firewall issue.

Thanks,
Preethi

On 03/12/20, 5:42 AM, "David Ahern" <dsahern@...il.com> wrote:

    [External Email. Be cautious of content]


    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://urldefense.com/v3/__https://elixir.bootlin.com/linux/latest/source/net/ipv6/ip6_output.c*L202__;Iw!!NEt6yMaO-gk!TTEMIr6Y_qiOz_QY3_Fh4QnRglxHEfu1mwoSo_Sve_Q6rdpmCMaf3l8ZCBNAnN4W$
    > 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://urldefense.com/v3/__https://elixir.bootlin.com/linux/latest/source/net/ipv6/ip6_output.c*L280__;Iw!!NEt6yMaO-gk!TTEMIr6Y_qiOz_QY3_Fh4QnRglxHEfu1mwoSo_Sve_Q6rdpmCMaf3l8ZCDcZbfyI$
    > 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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