Re: [PATCH v3] net: netfilter: Fix rpfilter dropping vrf packets by mistake

[Pablo Neira Ayuso]

On Thu, Apr 25, 2019 at 09:43:53PM +0800, linmiaohe wrote:
> From: Miaohe Lin <linmiaohe@xxxxxxxxxx>
> 
> When firewalld is enabled with ipv4/ipv6 rpfilter, vrf
> ipv4/ipv6 packets will be dropped because in device is
> vrf but out device is an enslaved device. So failed with
> the check of the rpfilter.
> 
> Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
> ---
>  net/ipv4/netfilter/ipt_rpfilter.c  |  1 +
>  net/ipv6/netfilter/ip6t_rpfilter.c | 10 +++++++++-
>  2 files changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/net/ipv4/netfilter/ipt_rpfilter.c b/net/ipv4/netfilter/ipt_rpfilter.c
> index 0b10d8812828..6e07cd0ecbec 100644
> --- a/net/ipv4/netfilter/ipt_rpfilter.c
> +++ b/net/ipv4/netfilter/ipt_rpfilter.c
> @@ -81,6 +81,7 @@ static bool rpfilter_mt(const struct sk_buff *skb, struct xt_action_param *par)
>  	flow.flowi4_mark = info->flags & XT_RPFILTER_VALID_MARK ? skb->mark : 0;
>  	flow.flowi4_tos = RT_TOS(iph->tos);
>  	flow.flowi4_scope = RT_SCOPE_UNIVERSE;
> +	flow.flowi4_oif = l3mdev_master_ifindex_rcu(xt_in(par));
> 
>  	return rpfilter_lookup_reverse(xt_net(par), &flow, xt_in(par), info->flags) ^ invert;
>  }
> diff --git a/net/ipv6/netfilter/ip6t_rpfilter.c b/net/ipv6/netfilter/ip6t_rpfilter.c
> index c3c6b09acdc4..a28c81322148 100644
> --- a/net/ipv6/netfilter/ip6t_rpfilter.c
> +++ b/net/ipv6/netfilter/ip6t_rpfilter.c
> @@ -58,7 +58,9 @@ static bool rpfilter_lookup_reverse6(struct net *net, const struct sk_buff *skb,
>  	if (rpfilter_addr_linklocal(&iph->saddr)) {
>  		lookup_flags |= RT6_LOOKUP_F_IFACE;
>  		fl6.flowi6_oif = dev->ifindex;
> -	} else if ((flags & XT_RPFILTER_LOOSE) == 0)
> +	} else if (((flags & XT_RPFILTER_LOOSE) == 0) ||
> +		   (netif_is_l3_master(dev)) ||
> +		   (netif_is_l3_slave(dev)))
>  		fl6.flowi6_oif = dev->ifindex;
> 
>  	rt = (void *)ip6_route_lookup(net, &fl6, skb, lookup_flags);
> @@ -73,6 +75,12 @@ 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;
> +	}

So, for the l3 device cases this makes:

#1 ip6_route_lookup() to fetch the route, using the device in xt_in()
   (the _LOOSE flag is ignored for the l3 device case).

#2 If this is a l3dev master, then you make a global lookup for the
   device using IP6CB(skb)->iif.

#3 You check if route matches with the device, using the new device
   from the lookup:

   if (rt->rt6i_idev->dev == dev ...

If there is no other way to fix this, OK, that's fair enough.

Still this fix looks a bit tricky to me.

And this assymmetric between the IPv4 and IPv6 codebase looks rare.

Probably someone can explain me this in more detail? I'd appreciate.

Thanks!