netdev - Re: [PATCH net-next 06/15] ipv4: Merge ip_local_out and ip_local_out

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Date:	Thu, 8 Oct 2015 11:38:56 +0200
From:	Nicolas Dichtel <nicolas.dichtel@...nd.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	David Miller <davem@...emloft.net>,
	netfilter-devel@...r.kernel.org, netdev@...r.kernel.org,
	lvs-devel@...r.kernel.org, Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH net-next 06/15] ipv4: Merge ip_local_out and
 ip_local_out_sk

Le 07/10/2015 22:39, Eric W. Biederman a écrit :
> Nicolas Dichtel <nicolas.dichtel@...nd.com> writes:
>
>> Le 06/10/2015 20:53, Eric W. Biederman a écrit :
>>> It is confusing and silly hiding a paramater so modify all of
>>> the callers to pass in the appropriate socket or skb->sk if
>>> no socket is known.
>>>
>>> Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
>>> ---
>> [snip]
>>> @@ -456,7 +456,7 @@ packet_routed:
>>>    	skb->priority = sk->sk_priority;
>>>    	skb->mark = sk->sk_mark;
>>>
>>> -	res = ip_local_out(skb);
>>> +	res = ip_local_out(sk, skb);
>> As stated in the comment at the top of this function (ip_queue_xmit()), skb->sk
>> can be different from sk. See also commit b0270e91014d ("ipv4: add a sock
>> pointer to ip_queue_xmit()").
>> Not sure if this change is right.
>
> Good catch.  This change should not have been buried in this patch. It
> needs to be it's own separate bug fix.
>
> As I read the code we actually do want to pass sk not skb->sk into
> ip_local_out.  For all of the reasons that sk is potentially different
> from skb->sk already.
>
> The way I understand this is we have pushed an sk parameter through the
> output path so that sk_mc_loop(sk) can be called with the tunnel's
> socket not whatever is on skb->sk.  This allows for looking to see if
> local multicast loopback is configured on the tunnels socket not on the
> originating socket of the packet.
Ok, thank you for the explanation.
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