netdev - Re: [PATCH net] vrf: reset rt_iif for recirculated mcast out pkts

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Message-ID: <e5813b87-51c7-d24f-94ec-c18c2bbe6599@gmail.com>
Date:   Tue, 25 Jun 2019 14:36:59 -0600
From:   David Ahern <dsahern@...il.com>
To:     Stephen Suryaputra <ssuryaextr@...il.com>, netdev@...r.kernel.org
Subject: Re: [PATCH net] vrf: reset rt_iif for recirculated mcast out pkts

On 6/25/19 2:22 PM, David Ahern wrote:
> On 6/25/19 4:33 AM, Stephen Suryaputra wrote:
>> @@ -363,10 +376,20 @@ int ip_mc_output(struct net *net, struct sock *sk, struct sk_buff *skb)
>>  #endif
>>  		   ) {
>>  			struct sk_buff *newskb = skb_clone(skb, GFP_ATOMIC);
>> -			if (newskb)
>> +			if (newskb) {
>> +				/* Reset rt_iif so that inet_iif() will return
>> +				 * skb->dev->ifIndex which is the VRF device for
>> +				 * socket lookup. Setting this to VRF ifindex
>> +				 * causes ipi_ifindex in in_pktinfo to be
>> +				 * overwritten, see ipv4_pktinfo_prepare().
>> +				 */
>> +				if (netif_is_l3_slave(dev))
> 
> seems like the rt_iif is a problem for recirculated mcast packets in
> general, not just ones tied to a VRF.
> 
>> +					ip_mc_reset_rt_iif(net, rt, newskb);
>> +
>>  				NF_HOOK(NFPROTO_IPV4, NF_INET_POST_ROUTING,
>>  					net, sk, newskb, NULL, newskb->dev,
>>  					ip_mc_finish_output);
>> +			}
>>  		}
>>  
>>  		/* Multicasts with ttl 0 must not go beyond the host */

Also, wouldn't this problem apply to broadcast packets as well if they
get recirculated back up the stack? Maybe then the reset_rt_iif needs to
be done in ip_mc_finish_output.