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Message-ID: <1b0e4a8c-76c5-061b-5222-ca4e3b971ec6@candelatech.com>
Date: Thu, 10 Mar 2022 18:41:08 -0800
From: Ben Greear <greearb@...delatech.com>
To: David Ahern <dsahern@...il.com>, netdev <netdev@...r.kernel.org>
Subject: Re: vrf and multicast problem
On 3/10/22 5:41 PM, Ben Greear wrote:
> On 3/10/22 3:41 PM, Ben Greear wrote:
>> On 3/10/22 12:03 PM, David Ahern wrote:
>>> On 3/10/22 12:33 PM, Ben Greear wrote:
>>>> On 3/9/22 7:54 PM, David Ahern wrote:
>>>>> On 3/9/22 3:31 PM, Ben Greear wrote:
>>>>>> [resend, sorry...sent to wrong mailing list the first time]
>>>>>>
>>>>>> Hello,
>>>>>>
>>>>>> We recently found a somewhat weird problem, and before I go digging into
>>>>>> the kernel source, I wanted to see if someone had an answer already...
>>>>>>
>>>>>> I am binding (SO_BINDTODEVICE) a socket to an Ethernet port that is in a
>>>>>> VRF with a second
>>>>>> interface. When I try to send mcast traffic out that eth port,
>>>>>> nothing is
>>>>>> seen on the wire.
>>>>>>
>>>>>> But, if I set up a similar situation with a single network port in
>>>>>> a vrf and send multicast, then it does appear to work as I expected.
>>>>>>
>>>>>> I am not actually trying to do any mcast routing here, I simply want to
>>>>>> send
>>>>>> out mcast frames from a port that resides inside a vrf.
>>>>>>
>>>>>> Any idea what might be the issue?
>>>>>>
>>>>>
>>>>> multicast with VRF works. I am not aware of any known issues
>>>>
>>>> I set up a more controlled network to do some more testing. I have eth2
>>>> on 192.168.100.x/24 network, and eth1 on 172.16.0.1/16.
>>>>
>>>> I bind the mcast transmitter to eth1:
>>>>
>>>> 193 setsockopt(28, SOL_SOCKET, SO_BINDTODEVICE,
>>>> "eth1\0\0\0\0\0\0\0\0\0\0\0\0", 16) = 0
>>>> 194 setsockopt(28, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
>>>> 195 bind(28, {sa_family=AF_INET, sin_port=htons(8888),
>>>> sin_addr=inet_addr("0.0.0.0")}, 16) = 0
>>>> 196 fcntl(28, F_GETFL) = 0x2 (flags O_RDWR)
>>>> 197 fcntl(28, F_SETFL, O_ACCMODE|O_NONBLOCK) = 0
>>>> 198 setsockopt(28, SOL_SOCKET, SO_BROADCAST, [1], 4) = 0
>>>> 199 setsockopt(28, SOL_SOCKET, SO_SNDBUF, [64000], 4) = 0
>>>> 200 setsockopt(28, SOL_SOCKET, SO_RCVBUF, [128000], 4) = 0
>>>> 201 getsockopt(28, SOL_SOCKET, SO_RCVBUF, [256000], [4]) = 0
>>>> 202 getsockopt(28, SOL_SOCKET, SO_SNDBUF, [128000], [4]) = 0
>>>> 203 write(3, "1646940176442: BtbitsIpEndpoint"..., 69) = 69
>>>> 204 setsockopt(28, SOL_IP, IP_TOS, [0], 4) = 0
>>>> 205 getsockopt(28, SOL_IP, IP_TOS, [0], [4]) = 0
>>>> 206 setsockopt(28, SOL_SOCKET, SO_PRIORITY, [0], 4) = 0
>>>> 207 getsockopt(28, SOL_SOCKET, SO_PRIORITY, [0], [4]) = 0
>>>> 208 write(3, "1646940176442: UdpEndpBase.cc 2"..., 148) = 148
>>>> 209 setsockopt(28, SOL_IP, IP_MULTICAST_IF, [16781484], 4) = 0
>>>> 210 setsockopt(28, SOL_IP, IP_MULTICAST_TTL, " ", 1) = 0
>>>>
>>>> That IP_MULTICAST_IF ioctl should be assigning the IP address of
>>>> eth1.
>>>>
>>>> But when I sniff, I see the mcast packets going out of eth2:
>>>>
>>>> [root@...22-63e7 lanforge]# tshark -n -i eth2
>>>> Running as user "root" and group "root". This could be dangerous.
>>>> Capturing on 'eth2'
>>>> 1 0.000000000 192.168.100.28 → 225.5.5.1 LANforge 1514 Seq: 474
>>>> 2 0.060868103 192.168.100.226 → 192.168.100.255 ADwin Config 94
>>>> 3 0.060900503 00:0d:b9:41:6a:90 → ff:ff:ff:ff:ff:ff 0x1111 92
>>>> Ethernet II
>>>> 4 0.209523669 192.168.100.28 → 225.5.5.1 LANforge 1514 Seq: 475
>>>>
>>>> [root@...22-63e7 lanforge]# ifconfig eth1
>>>> eth1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
>>>> inet 172.16.0.1 netmask 255.255.0.0 broadcast 172.16.255.255
>>>> inet6 fe80::230:18ff:fe01:63e8 prefixlen 64 scopeid 0x20<link>
>>>> ether 00:30:18:01:63:e8 txqueuelen 1000 (Ethernet)
>>>> RX packets 1972669 bytes 409744407 (390.7 MiB)
>>>> RX errors 0 dropped 0 overruns 0 frame 0
>>>> TX packets 5818525 bytes 7341747933 (6.8 GiB)
>>>> TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
>>>> device memory 0xdf740000-df75ffff
>>>>
>>>> [root@...22-63e7 lanforge]# ifconfig eth2
>>>> eth2: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
>>>> inet 192.168.100.28 netmask 255.255.255.0 broadcast
>>>> 192.168.100.255
>>>> inet6 fe80::230:18ff:fe01:63e9 prefixlen 64 scopeid 0x20<link>
>>>> ether 00:30:18:01:63:e9 txqueuelen 1000 (Ethernet)
>>>> RX packets 24638831 bytes 8874820766 (8.2 GiB)
>>>> RX errors 26712 dropped 6596663 overruns 0 frame 16757
>>>> TX packets 1753211 bytes 370552564 (353.3 MiB)
>>>> TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
>>>> device memory 0xdf720000-df73ffff
>>>>
>>>> If I disable VRF and use routing-rules based approach, then it works
>>>> as I expect (mcast frames go out of eth1).
>>>>
>>>> We tested back to quite-old kernels with same symptom, so I think it is not
>>>> a regression.
>>>>
>>>> Any suggestions on where to start poking at this in the kernel?
>>>>
>>>
>>> can you reproduce this using namespaces and veth pairs? if so, send me
>>> the script and I will take a look.
>>
>> I think debugging it will be easier than writing something for you to
>> reproduce it...
>>
>> I have tracked it down to this code in route.c:
>>
>> if (fl4->flowi4_oif) {
>> dev_out = dev_get_by_index_rcu(net, fl4->flowi4_oif);
>> rth = ERR_PTR(-ENODEV);
>> if (!dev_out)
>> goto out;
>>
>> /* RACE: Check return value of inet_select_addr instead. */
>> if (!(dev_out->flags & IFF_UP) || !__in_dev_get_rcu(dev_out)) {
>> rth = ERR_PTR(-ENETUNREACH);
>> goto out;
>> }
>> if (ipv4_is_local_multicast(fl4->daddr) ||
>> ipv4_is_lbcast(fl4->daddr) ||
>> fl4->flowi4_proto == IPPROTO_IGMP) {
>> if (!fl4->saddr)
>> fl4->saddr = inet_select_addr(dev_out, 0,
>> RT_SCOPE_LINK);
>> goto make_route;
>> }
>> if (!fl4->saddr) {
>> if (ipv4_is_multicast(fl4->daddr))
>> fl4->saddr = inet_select_addr(dev_out, 0,
>> fl4->flowi4_scope);
>> else if (!fl4->daddr)
>> fl4->saddr = inet_select_addr(dev_out, 0,
>> RT_SCOPE_HOST);
>> }
>> }
>>
>> if (!fl4->daddr) {
>> fl4->daddr = fl4->saddr;
>> if (!fl4->daddr)
>> fl4->daddr = fl4->saddr = htonl(INADDR_LOOPBACK);
>> dev_out = net->loopback_dev;
>> fl4->flowi4_oif = LOOPBACK_IFINDEX;
>> res->type = RTN_LOCAL;
>> flags |= RTCF_LOCAL;
>> goto make_route;
>> }
>>
>> pr_info("ip-route-output-key-hash-rcu before fib_lookup: orig_oif: %d fl4 oif: %d\n",
>> orig_oif, fl4->flowi4_oif);
>>
>> err = fib_lookup(net, fl4, res, 0);
>>
>> pr_info("ip-route-output-key-hash-rcu after fib_lookup: orig_oif: %d fl4 oif: %d err: %d\n",
>> orig_oif, fl4->flowi4_oif, err);
>>
>>
>> dmesg output:
>>
>>
>> [ 54.122391] UDP: udp-sendmsg, mcast, oif: 4 saddr: 0x0
>> [ 54.122399] UDP: udp-sendmsg, after, mcast, oif: 4 saddr: 0x10010ac
>> [ 54.122401] UDP: udp-sendmsg: after flowi4_init_output: oif: 4
>> [ 54.122404] UDP: udp-sendmsg: after security-sk-classify: oif: 4
>>
>> [ 54.122406] IPv4: ip-route-output-key-hash-rcu before fib_lookup: orig_oif: 4 fl4 oif: 4
>> ### This is the transition from expected to funky.
>> [ 54.122413] IPv4: ip-route-output-key-hash-rcu after fib_lookup: orig_oif: 4 fl4 oif: 21
>>
>> [ 54.122415] IPv4: ip-route-output-key-hash-rcu before fib_select_path: orig_oif: 4 fl4 oif: 21
>> [ 54.122418] IPv4: ip-route-output-key-hash-rcu after fib_select_path: orig_oif: 4 fl4 oif: 21
>> [ 54.122420] IPv4: ip-route-output-key-hash-rcu make_route Before, orig_oif: 4 fl4 oif: 21 dev_out: 5
>> [ 54.122443] IPv4: ip-route-output-key-hash-rcu make_route After, orig_oif: 4 fl4 oif: 21 dev_out: 5
>> [ 54.122446] IPv4: ip_route_output_flow, old-oif: 21 new: 5 new-dev: eth2
>> [ 54.122449] UDP: udp-sendmsg: after ip_route_output_flow: oif: 5
>>
>>
>> So, something in the fib_lookup code is selecting the vrf device as output,
>> I guess because oif 4 (eth1) is part of the vrf. And then the vrf routing table
>> ends up selecting oif 5 (eth2), which holds the default route. However, there is
>> nothing adding any mcast routing (I am not running any multicast router on this vrf),
>> so once the code forgets that I bound the socket to oif 4, then it ends up choosing
>> the wrong outbound interface.
>>
>> In the paste above, there is special casing for 'local' mcast routing. If I select
>> a 224.0.0.x local mcast address, then the special case code is used and then things
>> work as I expected (mcast pkts go out of the selected interface).
>>
>> I think that maybe other mcast addresses should also abide by the user's request if user
>> has bound it to a specified oif?
>>
>> Or, maybe there is some special casing needed in the fib_lookup?
>
> After some more investigation of this code, I am questioning the need for this logic:
>
> /* update flow if oif or iif point to device enslaved to l3mdev */
> l3mdev_update_flow(net, flowi4_to_flowi(flp));
>
> If I bind a socket to a particular net-dev with SO_BINDTODEVICE, then I really
> do want to force the frame out that interface.
>
> I understand that with vrf, there is a secondary meaning that when you bind to
> a device that is part of a vrf, then you are also associating with that vrf.
> To me, this should mean that we use the routing table associated with this
> vrf, but just like when using 'normal' routing tables, binding to specify an OIF
> takes precedence over a lot of the routing logic.
>
> If a user wishes to send frames and have the vrf route the frame out arbitrary interface, then it could
> bind to the vrf device itself. Or maybe you could let the vrf device be the oif
> if source-addr is not selected, but that is pretty subtle distinction as well.
>
> And all this said, I am still not understanding how the vrf is supposed to make
> an intelligent decision on mcast routing in this situation.
>
> Thanks,
> Ben
>
>
This hack upon a hack makes my multicast test work for me (tm).
My real diff is full of debugging, so just assume you see the code where I pass in the
original netdev. I'll post a cleaned up patch tomorrow:
in __mkroute_output from ipv4/route.c:
My stuff starts with the logic related to orig_dev_out:
...
} else if (type == RTN_MULTICAST) {
flags |= RTCF_MULTICAST | RTCF_LOCAL;
if (!ip_check_mc_rcu(in_dev, fl4->daddr, fl4->saddr,
fl4->flowi4_proto)) {
flags &= ~RTCF_LOCAL;
pr_info("removing RTCF_LOCAL flag\n");
}
else {
do_cache = false;
pr_info("not removing RTCF_LOCAL flag, do_cache to false\n");
}
pr_info("res->prefixlen: %d fi: %p\n",
res->prefixlen, fi);
/* If multicast route do not exist use
* default one, but do not gateway in this case.
* Yes, it is hack.
*/
if (fi && res->prefixlen < 4) {
struct net *net = dev_net(dev_out);
fi = NULL;
if (orig_oif && orig_dev_out &&
dev_out->ifindex != orig_oif &&
netif_index_is_l3_master(net, fl4->flowi4_oif)) {
/* vrf overwrites the original flowi4_oif for
* member network devices. In that case,
* lets use the user-specified oif instead of
* a default route.
*/
dev_out = orig_dev_out;
}
}
It does not solve all of my concerns about binding unicast sockets, but I've been dealing with
that mostly successfully already, so maybe this hack will be good enough...
Thanks,
Ben
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