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

To: Nicolas Dichtel <nicolas.dichtel@xxxxxxxxx>
Subject: Re: [PATCH net-next 06/15] ipv4: Merge ip_local_out and ip_local_out_sk
Cc: David Miller <davem@xxxxxxxxxxxxx>, netfilter-devel@xxxxxxxxxxxxxxx, netdev@xxxxxxxxxxxxxxx, lvs-devel@xxxxxxxxxxxxxxx, Eric Dumazet <eric.dumazet@xxxxxxxxx>
From: ebiederm@xxxxxxxxxxxx (Eric W. Biederman)
Date: Wed, 07 Oct 2015 15:39:52 -0500
Nicolas Dichtel <nicolas.dichtel@xxxxxxxxx> 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@xxxxxxxxxxxx>
>> ---
> [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.

I am going to respin my series with that change made into a separate bug
fix, that can potentially be backported.


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