[PATCH] netfilter: rpfilter: skip locally generated bcast, too

[PATCH] netfilter: rpfilter: skip locally generated bcast, too

[Florian Westphal]

Alex Efros reported rpfilter module doesn't match following packets:
IN=br.qemu SRC=192.168.2.1 DST=192.168.2.255 [ .. ]
(netfilter bugzilla #814).

Problem is that network stack arranges for the locally generated broadcasts
to appear on the interface they were sent out, so the IFF_LOOPBACK check
doesn't trigger.

As -m rpfilter is restricted to PREROUTING, we can check for existing
skb_dst instead, it catches locally-generated broad/multicast case, too.

Signed-off-by: Florian Westphal <fw@strlen.de>
---
 net/ipv4/netfilter/ipt_rpfilter.c  |    2 +-
 net/ipv6/netfilter/ip6t_rpfilter.c |    2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/netfilter/ipt_rpfilter.c b/net/ipv4/netfilter/ipt_rpfilter.c
index c301300..601abf2 100644
--- a/net/ipv4/netfilter/ipt_rpfilter.c
+++ b/net/ipv4/netfilter/ipt_rpfilter.c
@@ -76,7 +76,7 @@ static bool rpfilter_mt(const struct sk_buff *skb, struct xt_action_param *par)
 	info = par->matchinfo;
 	invert = info->flags & XT_RPFILTER_INVERT;
 
-	if (par->in->flags & IFF_LOOPBACK)
+	if (skb_dst(skb)) /* locally generated? */
 		return true ^ invert;
 
 	iph = ip_hdr(skb);
diff --git a/net/ipv6/netfilter/ip6t_rpfilter.c b/net/ipv6/netfilter/ip6t_rpfilter.c
index 5060d54..8767991 100644
--- a/net/ipv6/netfilter/ip6t_rpfilter.c
+++ b/net/ipv6/netfilter/ip6t_rpfilter.c
@@ -78,7 +78,7 @@ static bool rpfilter_mt(const struct sk_buff *skb, struct xt_action_param *par)
 	struct ipv6hdr *iph;
 	bool invert = info->flags & XT_RPFILTER_INVERT;
 
-	if (par->in->flags & IFF_LOOPBACK)
+	if (skb_dst(skb)) /* locally generated? */
 		return true ^ invert;
 
 	iph = ipv6_hdr(skb);
-- 
1.7.8.6

Re: [PATCH] netfilter: rpfilter: skip locally generated bcast, too

[Pablo Neira Ayuso]

Hi Florian,

On Fri, Apr 12, 2013 at 10:51:31PM +0200, Florian Westphal wrote:
> Alex Efros reported rpfilter module doesn't match following packets:
> IN=br.qemu SRC=192.168.2.1 DST=192.168.2.255 [ .. ]
> (netfilter bugzilla #814).
> 
> Problem is that network stack arranges for the locally generated broadcasts
> to appear on the interface they were sent out, so the IFF_LOOPBACK check
> doesn't trigger.
> 
> As -m rpfilter is restricted to PREROUTING, we can check for existing
> skb_dst instead, it catches locally-generated broad/multicast case, too.
> 
> Signed-off-by: Florian Westphal <fw@strlen.de>
> ---
>  net/ipv4/netfilter/ipt_rpfilter.c  |    2 +-
>  net/ipv6/netfilter/ip6t_rpfilter.c |    2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/net/ipv4/netfilter/ipt_rpfilter.c b/net/ipv4/netfilter/ipt_rpfilter.c
> index c301300..601abf2 100644
> --- a/net/ipv4/netfilter/ipt_rpfilter.c
> +++ b/net/ipv4/netfilter/ipt_rpfilter.c
> @@ -76,7 +76,7 @@ static bool rpfilter_mt(const struct sk_buff *skb, struct xt_action_param *par)
>  	info = par->matchinfo;
>  	invert = info->flags & XT_RPFILTER_INVERT;
>  
> -	if (par->in->flags & IFF_LOOPBACK)
> +	if (skb_dst(skb)) /* locally generated? */

I'd prefer if this is narrowed down to locally generated traffic in
the same way we do in nf_conntrack_broadcast.c.

Re: [PATCH] netfilter: rpfilter: skip locally generated bcast, too

[Florian Westphal]

Pablo Neira Ayuso <pablo@netfilter.org> wrote:
> Hi Florian,
> 
> > diff --git a/net/ipv4/netfilter/ipt_rpfilter.c b/net/ipv4/netfilter/ipt_rpfilter.c
> > index c301300..601abf2 100644
> > --- a/net/ipv4/netfilter/ipt_rpfilter.c
> > +++ b/net/ipv4/netfilter/ipt_rpfilter.c
> > @@ -76,7 +76,7 @@ static bool rpfilter_mt(const struct sk_buff *skb, struct xt_action_param *par)
> >  	info = par->matchinfo;
> >  	invert = info->flags & XT_RPFILTER_INVERT;
> >  
> > -	if (par->in->flags & IFF_LOOPBACK)
> > +	if (skb_dst(skb)) /* locally generated? */
> 
> I'd prefer if this is narrowed down to locally generated traffic in
> the same way we do in nf_conntrack_broadcast.c.

Fair enough, i will change it.