Re: [PATCH v2] net: netfilter: Fix ipv6 rp_filter dropping vrf packets by mistake

[David Ahern]

On 4/24/19 3:12 AM, linmiaohe wrote:
> From: Miaohe Lin <linmiaohe@xxxxxxxxxx>
> 
> When firewall is enabled with rp_filter, vrf ipv6 packets
> will be dropped because in device is vrf but out device
> is an enslaved device. So rt->rt6i_idev->dev != dev and
> maybe return false in func rpfilter_lookup_reverse6.
> 
> Here is the out message when I ping the peer:
> ip vrf exec vrf1 ping 2013::2 -c 1
> 1 packets transmitted, 0 received, 100% packet loss, time 0ms
> 
> The drop info in /var/log/message:
> Apr 24 14:59:45 localhost kernel: [81316.158259] rpfilter_DROP: IN=vrf1
> OUT= MAC=52:54:00:9e:dd:c1:52:54:00:4f:81:38:86:dd
> SRC=2013:0000:0000:0000:0000:0000:0000:0002
> DST=2013:0000:0000:0000:0000:0000:0000:0001 LEN=104 TC=0 HOPLIMIT=64
> FLOWLBL=1032942 PROTO=ICMPv6 TYPE=129 CODE=0 ID=14943 SEQ=1
> 
> Signed-off-by: linmiaohe <linmiaohe@xxxxxxxxxx>
> ---
>  net/ipv6/netfilter/ip6t_rpfilter.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/net/ipv6/netfilter/ip6t_rpfilter.c b/net/ipv6/netfilter/ip6t_rpfilter.c
> index c3c6b09acdc4..cf1070ab1252 100644
> --- a/net/ipv6/netfilter/ip6t_rpfilter.c
> +++ b/net/ipv6/netfilter/ip6t_rpfilter.c
> @@ -73,6 +73,12 @@ static bool rpfilter_lookup_reverse6(struct net *net, const struct sk_buff *skb,
>  		goto out;
>  	}
> 
> +	if (netif_is_l3_master(dev)) {
> +		dev = dev_get_by_index_rcu(dev_net(dev), IP6CB(skb)->iif);
> +		if (!dev)
> +			goto out;
> +	}
> +
>  	if (rt->rt6i_idev->dev == dev || (flags & XT_RPFILTER_LOOSE))
>  		ret = true;
>   out:
> 

What about the case where XT_RPFILTER_LOOSE is set? flowi6_oif needs to
be set to the dev->ifindex if dev is an l3 master.

And looking at the IPv4 version I do not see how it could be correct
either. Have you tested it?