netdev - Re: [PATCHv2 net-next 2/2] selftests: add a selftest for directed broadcast forwarding

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Message-ID: <CADvbK_fsFHuW4gvtpSZ-A8F12PXaMX8YGGKmhsMy3L_KTZt-8Q@mail.gmail.com>
Date:   Thu, 5 Jul 2018 15:57:52 +0800
From:   Xin Long <lucien.xin@...il.com>
To:     David Ahern <dsahern@...il.com>
Cc:     network dev <netdev@...r.kernel.org>, davem <davem@...emloft.net>,
        Davide Caratti <dcaratti@...hat.com>,
        Ido Schimmel <idosch@...sch.org>
Subject: Re: [PATCHv2 net-next 2/2] selftests: add a selftest for directed
 broadcast forwarding

On Thu, Jul 5, 2018 at 2:36 AM, David Ahern <dsahern@...il.com> wrote:
> On 7/4/18 11:56 AM, Xin Long wrote:
>
>>> your commands are not a proper test. The test should succeed and fail
>>> based on the routing lookup, not iptables rules.
>> A proper test can be done easily with netns, as vrf can't isolate much.
>> I don't want to bother forwarding/ directory with netns, so I will probably
>> just drop this selftest, and let the feature patch go first.
>>
>
> BTW, VRF isolates at the routing layer and this is a routing change. We
> need to understand why it does not work with VRF. Perhaps another tweak
> is needed for VRF.
One problem was that the peer may not use the address on the dev
that echo_request comes from as the src IP of echo_reply when the
echo_request's dst IP is broadcast, but try to get another one by
looking up a route without ".flowi4_oif" set. See:

icmp_reply()->fib_compute_spec_dst():
                struct flowi4 fl4 = {
                        .flowi4_iif = LOOPBACK_IFINDEX,
                        .daddr = ip_hdr(skb)->saddr,
                        .flowi4_tos = RT_TOS(ip_hdr(skb)->tos),
                        .flowi4_scope = scope,
                        .flowi4_mark = IN_DEV_SRC_VMARK(in_dev) ? skb->mark : 0,
                };
                if (!fib_lookup(net, &fl4, &res, 0))
                        return FIB_RES_PREFSRC(net, res);


Without ".flowi4_oif" set, it won't match the vrf route. That's why
I had to make h2 NOT into a vrf so that h1 can get the echo_reply.
But it can't tell if this echo_reply is from h2 or r1, as r1's echo_reply
will also use the same src IP which is actually got from main route
space as  ".flowi4_oif" is not set.
(hope I this description is clear to you) :)

So i'm not sure if we can do any tweak for VRF.