From: 曹煜 <cao88yu@gmail.com>
To: "Daniel Gröber" <dxld@darkboxed.org>
Cc: Nico Schottelius <nico.schottelius@ungleich.ch>,
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 08:28:48 +0800 [thread overview]
Message-ID: <CACu-5+0+7h5XjM1xVjK+frwF=dOteoa+wuw_vhesJ7_ek1vfjQ@mail.gmail.com> (raw)
In-Reply-To: <20230219224200.g5mwcaybee4hujov@House.clients.dxld.at>
Hi all,
I've hacked that source code myself months ago, and it works well on
my use case (I have 4 dual stack pppoe wan set on my openwrt router,
and seted a wireguard sever on it), my hack will pickup the dst_addr
from incoming handshake packet in kernel sk_buff, and then use that
addr as src_addr to reply.
I'm not good at source code, and I know that my hack may be ugly, but
it works, hope this patch can help:
https://github.com/openwrt/packages/issues/9538#issuecomment-1150592803
Daniel Gröber <dxld@darkboxed.org> 于2023年2月20日周一 06:42写道:
>
> Hi,
>
> I though it might be useful to do some quick and dirty code review instead
> of speculating wildly to figure out where these source IP selection
> problems could be coming from ;)
>
> From previous code deep dives I know the udp_tunnel_xmit_skb function is
> where tunnel packets get handed off to the kernel. So in
> net/wireguard/socket.c:send4 we have:
>
> udp_tunnel_xmit_skb(rt, sock, skb, fl.saddr, fl.daddr, ds,
> ip4_dst_hoplimit(&rt->dst), 0, fl.fl4_sport,
> fl.fl4_dport, false, false);
>
> Where fl.saddr is the source address that's supposedly wrong (sometimes? I
> guess?) Where does that come from?
>
> 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);
> if (!rt) {
> if (unlikely(!inet_confirm_addr(sock_net(sock), NULL, 0,
> fl.saddr, RT_SCOPE_HOST)))
> fl.saddr = 0;
> if (unlikely(endpoint->src_if4 && ((IS_ERR(rt) &&
> PTR_ERR(rt) == -EINVAL) || (!IS_ERR(rt) &&
> rt->dst.dev->ifindex != endpoint->src_if4))))
> fl.saddr = 0;
>
> Well it's initialized from endpoint->src4.s_addr, overwritten with zero in
> some cases, which I believe lets the kernel do it's regular source addr
> selection, and populated from something called dst_cache at some callsites.
>
> @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?
>
> The first case !inet_confirm_addr(..., RT_SCOPE_HOST) ought to confirm that
> the saddr is actually still a local address. Makes sens if the address we
> remembered was removed from the interface we can't use it anymore.
>
> The second case looks like it's checking if the (sometimes cached) src_if4
> interface index is still what the route we're about to use points to.
>
> If neither of those seem likely we can keep reading :)
>
> --Daniel
>
>
>
next prev parent reply other threads:[~2023-02-20 0:29 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
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 [this message]
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
2023-02-19 21:39 ` Source IP incorrect on multi homed systems 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 20:02 ` Nico Schottelius
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