Re: [PATCH net-next 2/5] net: sched: em_ipt: set the family based on the protocol when matching

[Eyal Birger <eyal.birger@gmail.com>]

On Wed, 26 Jun 2019 16:45:28 +0300
Nikolay Aleksandrov <nikolay@cumulusnetworks.com> wrote:

> On 26/06/2019 16:33, Eyal Birger wrote:
> > Hi Nikolay,
> >    
> > On Wed, 26 Jun 2019 14:58:52 +0300
> > Nikolay Aleksandrov <nikolay@cumulusnetworks.com> wrote:
> >   
> >> Set the family based on the protocol otherwise protocol-neutral
> >> matches will have wrong information (e.g. NFPROTO_UNSPEC). In
> >> preparation for using NFPROTO_UNSPEC xt matches.
> >>
> >> Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
> >> ---
> >>  net/sched/em_ipt.c | 4 +++-
> >>  1 file changed, 3 insertions(+), 1 deletion(-)
> >>
...
> >> -	nf_hook_state_init(&state, im->hook, im->match->family,
> >> +	nf_hook_state_init(&state, im->hook, state.pf,
> >>  			   indev ?: skb->dev, skb->dev, NULL,
> >> em->net, NULL); 
> >>  	acpar.match = im->match;  
> > 
> > I think this change is incompatible with current behavior.
> > 
> > Consider the 'policy' match which matches the packet's xfrm state
> > (sec_path) with the provided user space parameters. The sec_path
> > includes information about the encapsulating packet's parameters
> > whereas the current skb points to the encapsulated packet, and the
> > match is done on the encapsulating packet's info.
> > 
> > So if you have an IPv6 packet encapsulated within an IPv4 packet,
> > the match parameters should be done using IPv4 parameters, not IPv6.
> > 
> > Maybe use the packet's family only if the match family is UNSPEC?
> > 
> > Eyal.
> >   
> 
> Hi Eyal,
> I see your point, I was wondering about the xfrm cases. :)
> In such case I think we can simplify the set and do it only on UNSPEC
> matches as you suggest.
> 
> Maybe we should enforce the tc protocol based on the user-specified
> nfproto at least from iproute2 otherwise people can add mismatching
> rules (e.g. nfproto == v6, tc proto == v4).
> 
Hi Nik,

I think for iproute2 the issue is the same. For encapsulated IPv6 in
IPv4 for example, tc proto will be IPv6 (tc sees the encapsulated
packet after decryption) whereas nfproto will be IPv4 (policy match is
done on the encapsulating state metadata which is IPv4).

I think the part missing in iproute2 is the ability to specify
NFPROTO_UNSPEC.

Thanks,
Eyal