From: dxld@darkboxed.org
To: Nico Schottelius <nico.schottelius@ungleich.ch>
Cc: Roman Mamedov <rm@romanrm.net>, tlhackque <tlhackque@yahoo.com>,
wireguard@lists.zx2c4.com
Subject: Re: Src addr code review (Was: Source IP incorrect on multi homed systems)
Date: Mon, 20 Feb 2023 21:43:47 +0100 [thread overview]
Message-ID: <20230220204347.nqeusqotqtxbjiw2@House.clients.dxld.at> (raw)
In-Reply-To: <87leksbr5n.fsf@ungleich.ch>
Hi Nico,
On Mon, Feb 20, 2023 at 10:47:36AM +0100, Nico Schottelius wrote:
> Daniel Gröber <dxld@darkboxed.org> writes:
> > Let's look at the code (heavily culled):
> >
> > struct flowi4 fl = {
> > .saddr = endpoint->src4.s_addr,
> > };
> > if (cache)
> > rt = dst_cache_get_ip4(cache, &fl.saddr);
>
> What I am wondering is, how did it get into the cache in the first place?
Right so, endpoint->src4 is set in wg_socket_set_peer_endpoint, which is
called either trough through wg_socket_endpoint_from_skb in the handshake
receive code or wg_socket_set_peer_endpoint in the data path.
The _from_skb variant also calls wg_socket_endpoint_from_skb. Here we're
remembering the src addr of the (received) packet in addr4 and the dst addr
we're going to use for sending as src4 as you'd expect:
endpoint->addr4.sin_family = AF_INET;
endpoint->addr4.sin_port = udp_hdr(skb)->source;
endpoint->addr4.sin_addr.s_addr = ip_hdr(skb)->saddr;
endpoint->src4.s_addr = ip_hdr(skb)->daddr;
endpoint->src_if4 = skb->skb_iif;
The dst_cache is set just after those zero'ing conditionals we were looking
at before. It's cleared whenever the endpoint/port changes or one of those
cases is hit. Note the dst_cache is only used for data packets, so
handshakes would be unaffected if it was the cause of your woes.
> > @Nico could it perhaps simply be that you're hitting one of these zero'ing
> > cases and that's why it's using regular kernel src addr selection instead
> > of the cached endpoint src4 address?
>
> That could absolutely be the case. What is funky is that I see the
> problem on two very different systems
>
> Both systems exhibit the behaviour, but maybe it's better to focus on
> System A first, as this seems to be more the "upstream" source.
It is weird indeed, but yeah. One thing at a time.
BTW, what kernel version/distro are we dealing with?
--Daniel
next prev parent reply other threads:[~2023-02-20 20:43 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-18 20:14 Source IP incorrect on multi homed systems Nico Schottelius
[not found] ` <CAHx9msc1cNV80YU7HRmQ9gsjSEiVZ=pb31aYqfP62hy8DeuGZA@mail.gmail.com>
2023-02-18 22:34 ` Nico Schottelius
2023-02-19 0:45 ` Mike O'Connor
2023-02-19 8:01 ` Nico Schottelius
2023-02-19 9:19 ` Mikma
2023-02-19 12:04 ` Nico Schottelius
2023-02-19 12:10 ` Nico Schottelius
2023-02-19 18:59 ` Peter Linder
[not found] ` <2ed829aaed9fec59ac2a9b32c4ce0a9005b8d8b850be81c81a226791855fe4eb@mu.id>
2023-02-19 12:13 ` Nico Schottelius
2023-02-19 14:39 ` Christoph Loesch
2023-02-19 16:32 ` David Kerr
2023-02-19 16:54 ` Sebastian Hyrvall
2023-02-19 18:04 ` Janne Johansson
2023-02-19 18:08 ` Sebastian Hyrvall
2023-02-19 20:11 ` Nico Schottelius
2023-02-19 17:05 ` tlhackque
[not found] ` <CADGd2DoE6TCtCxxWL7JWyNW5+yy_Pe+9MNzHznbudMWLTXQreA@mail.gmail.com>
2023-02-19 18:30 ` Fwd: " John Lauro
2023-02-19 22:28 ` tlhackque
2023-02-20 0:58 ` Luiz Angelo Daros de Luca
2023-02-19 18:37 ` David Kerr
2023-02-19 18:52 ` tlhackque
2023-02-19 18:42 ` tlhackque
2023-02-19 20:18 ` Nico Schottelius
2023-02-19 20:42 ` Roman Mamedov
2023-02-19 21:19 ` Nico Schottelius
2023-02-19 22:06 ` tlhackque
2023-02-19 22:42 ` Src addr code review (Was: Source IP incorrect on multi homed systems) Daniel Gröber
2023-02-20 0:28 ` 曹煜
2023-02-20 10:40 ` Nico Schottelius
2023-02-20 11:21 ` 曹煜
2023-02-20 9:47 ` Nico Schottelius
2023-02-20 20:43 ` dxld [this message]
2023-02-19 21:39 ` Source IP incorrect on multi homed systems tlhackque
2023-02-19 20:02 ` Nico Schottelius
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