netdev - Re: [PATCH] net: fix incorrect original ingress device index in PKTINFO

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Date:   Tue, 27 Dec 2016 13:01:29 +0300
From:   Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:     Wei Zhang <asuka.com@....com>, davem@...emloft.net,
        kuznet@....inr.ac.ru, jmorris@...ei.org, yoshfuji@...ux-ipv6.org,
        kaber@...sh.net
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: fix incorrect original ingress device index in
 PKTINFO

Hello!

On 12/27/2016 10:52 AM, Wei Zhang wrote:

> When we send a packet for our own local address on a non-loopback interface
> (e.g. eth0), due to the change had been introduced from commit 0b922b7a829c
> ("net: original ingress device index in PKTINFO"), the original ingress
> device index would be set as the loopback interface. However, the packet
> should be considered as if it is being arrived via the sending interface
> (eth0), otherwise it would break the expectation of the userspace
> application (e.g. the DHCPRELEASE message from dhcp_release binary would
> be ignored by the dnsmasq daemon)
>
> Signed-off-by: Wei Zhang <asuka.com@....com>
> ---
>  net/ipv4/ip_sockglue.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
> index b8a2d63..b6a6d35 100644
> --- a/net/ipv4/ip_sockglue.c
> +++ b/net/ipv4/ip_sockglue.c
> @@ -1202,8 +1202,13 @@ void ipv4_pktinfo_prepare(const struct sock *sk, struct sk_buff *skb)
>  		 * which has interface index (iif) as the first member of the
>  		 * underlying inet{6}_skb_parm struct. This code then overlays
>  		 * PKTINFO_SKB_CB and in_pktinfo also has iif as the first
> -		 * element so the iif is picked up from the prior IPCB
> +		 * element so the iif is picked up from the prior IPCB except
> +		 * iif is loopback interface which the packet should be

    Tail space.

> +		 * considered as if it is being arrived via the sending interface
>  		 */
> +		if (pktinfo->ipi_ifindex == LOOPBACK_IFINDEX) {
> +			pktinfo->ipi_ifindex = inet_iif(skb);
> +		}

    {} not needed here.

>  		pktinfo->ipi_spec_dst.s_addr = fib_compute_spec_dst(skb);
>  	} else {
>  		pktinfo->ipi_ifindex = 0;

MBR, Sergei