On Mon, Mar 02, 2015 at 02:36:47PM +0000, Patrick McHardy wrote:
> On 02.03, Pablo Neira Ayuso wrote:
> > On Mon, Mar 02, 2015 at 02:19:00PM +0000, Patrick McHardy wrote:
> > > On 02.03, Pablo Neira Ayuso wrote:
> > > > On Mon, Mar 02, 2015 at 01:19:01PM +0000, Patrick McHardy wrote:
> > > > > >
> > > > > > 3) SYMPROXY6. Don't check for e->ipv6.flags, we can instead check
> > > > > > for e->ipv6.proto as other extensions do, if zero then it doesn't
> > > > > > fulfill the dependency.
> > > > >
> > > > > But we don't perform a protocol match in ip6_tables if the IP6T_F_PROTO
> > > > > flag is not given. ip6_tables differs from ip_tables in this regard.
> > > >
> > > > This just makes sure that SYNPROXY6 is not called for non-tcp traffic
> > > > in the rule loading path, which should be OK.
> > >
> > > Yeah, but for ip6_tables we actually need the check the way it is,
> > > without IP6T_F_PROTO we will not perform the protocol match.
> >
> > if (!(e->ipv6.flags & IP6T_F_PROTO) ||
> > e->ipv6.proto != IPPROTO_TCP ||
> > e->ipv6.invflags & XT_INV_PROTO)
> > return -EINVAL;
> >
> > e->ipv6.flags & IP6T_F_PROTO seems redundant to me, it just says
> > e->ipv6.proto is set.
>
> No, it also instructs ip6_tables to actually match on that value.
>
> > If that flag is not set, then e->ipv6.proto is left unset. But the
> > effect should be the same since 0 != IPPROTO_TCP.
> >
> > This is just relaxing the validation in SYNPROXY6 to only check
> > e->ipv6.proto which is what nft_compat sets.
> >
> > Am I missing anything?
>
> Yes, ip6_tables only performs the protocol match when that flag is set.
> Look:
>
> /* look for the desired protocol header */
> if((ip6info->flags & IP6T_F_PROTO)) {
> ...
> if (ip6info->proto == protohdr) {
>
> This is where ip6_tables and ip_tables are different, ip_tables
> takes ipinfo->proto as an indicator, ip6_tables the flag.
I'm not altering the ip6_tables core logic.
ip6tables from userspace sets IP6T_F_PROTO, the core handles things as
you described, but SYNPROXY6 only checks if e->ipv6.proto != IPPROTO_TCP.
REJECT6 does exactly the same that I need:
if (e->ipv6.proto != IPPROTO_TCP ||
(e->ipv6.invflags & XT_INV_PROTO)) {
pr_info("TCP_RESET illegal for non-tcp\n");
return -EINVAL;
}
I just want to relax the check in SYNPROXY6, so it works fine with
nft_compat. I think nothing will break.
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