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

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Date:   Fri, 6 Jul 2018 17:50:28 +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 10:07 PM, Xin Long <lucien.xin@...il.com> wrote:
> On Thu, Jul 5, 2018 at 9:18 PM, David Ahern <dsahern@...il.com> wrote:
>> On 7/5/18 1:57 AM, Xin Long wrote:
>>> 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.
>>>
>>
>> Try this:
>>
>> diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_frontend.c
>> index b21833651394..e46cdd310e5f 100644
>> --- a/net/ipv4/fib_frontend.c
>> +++ b/net/ipv4/fib_frontend.c
>> @@ -300,6 +300,7 @@ __be32 fib_compute_spec_dst(struct sk_buff *skb)
>>         if (!ipv4_is_zeronet(ip_hdr(skb)->saddr)) {
>>                 struct flowi4 fl4 = {
>>                         .flowi4_iif = LOOPBACK_IFINDEX,
>> +                       .flowi4_oif = l3mdev_master_ifindex_rcu(dev),
>>                         .daddr = ip_hdr(skb)->saddr,
>>                         .flowi4_tos = RT_TOS(ip_hdr(skb)->tos),
>>                         .flowi4_scope = scope,
If this patch can be applied, I would be able to make a proper selftest like:

...
ping_test_from()
{
local oif=$1
local dip=$2
local from=$3
local fail=$4

RET=0

ip vrf exec $(master_name_get $oif) \
$PING -I $oif $dip -c 10 -i 0.1 -w 2 -b 2>&1 | grep $from &> /dev/null
check_err_fail $fail $?
log_test "ping_test_from"
}

ping_ipv4()
{
sysctl_set net.ipv4.icmp_echo_ignore_broadcasts 0

bc_forwarding_disable
ping_test_from $h1 198.51.100.255 192.0.2.1
ping_test_from $h1 198.51.200.255 192.0.2.1
ping_test_from $h1 192.0.2.255 192.0.2.1
ping_test_from $h1 255.255.255.255 192.0.2.1

ping_test_from $h2 192.0.2.255 198.51.100.1
ping_test_from $h2 198.51.200.255 198.51.100.1
ping_test_from $h2 198.51.100.255 198.51.100.1
ping_test_from $h2 255.255.255.255 198.51.100.1
bc_forwarding_restore

bc_forwarding_enable
ping_test_from $h1 198.51.100.255 198.51.100.2
ping_test_from $h1 198.51.200.255 198.51.200.2
ping_test_from $h1 192.0.2.255 192.0.2.1 1
ping_test_from $h1 255.255.255.255 192.0.2.1

ping_test_from $h2 192.0.2.255 192.0.2.2
ping_test_from $h2 198.51.200.255 198.51.200.2
ping_test_from $h2 198.51.100.255 198.51.100.1 1
ping_test_from $h2 255.255.255.255 198.51.100.1
bc_forwarding_restore

sysctl_restore net.ipv4.icmp_echo_ignore_broadcasts
}

> Great, with your fix, I can extend more for this selftest.
> but I hope no side effects would be caused.
>
> Thank you.