Wireguard uses incorrect interface - routing issue

[Daniel Gröber]

On Fri, Jun 21, 2024 at 01:24:47PM +0200, Nico Schottelius wrote:
> 
> p.s.: the route lookup looks correct on the machine, when selecting the
> source IP:
> 
> [11:15] server141.place10:~# ip r get 194.187.90.23
> 194.187.90.23 via inet6 fe80::3eec:efff:fecb:d81a dev eth0 src 192.168.1.149 uid 0 
>     cache 
> [11:16] server141.place10:~# ip r get 194.187.90.23 from 192.168.1.149
> 194.187.90.23 from 192.168.1.149 via 192.168.1.254 dev eth1 table 42 uid 0 
>     cache 
> 
> wireguard still uses the wrong interface:
> 
> 11:20:13.115154 eth0  Out IP 192.168.1.149.60031 > 194.187.90.23.4000: UDP, length 148

I haven't looked at the details yet but this smells like the same route
caching issue I found a while ago:
https://lists.zx2c4.com/pipermail/wireguard/2023-July/008111.html

Does up/down'ing the interface make the problem go away? IIRC that will
re-initialize the udp socket and thus clear the route chache.

FYI Nico: It may be time to escalate these bugs to the network subsystem
maintainers on netdev at vger.kernel.org since Jason is not reading this list
anymore AFAICT.

get_maintainer.pl spits out this list of emails to send To:

    Jason A. Donenfeld" <Jason at zx2c4.com>,
    "David S. Miller" <davem at davemloft.net>,
    Eric Dumazet <edumazet at google.com>, 
    Jakub Kicinski <kuba at kernel.org>,
    Paolo Abeni <pabeni at redhat.com>,
    wireguard at lists.zx2c4.com, 
    netdev at vger.kernel.org,
    linux-kernel at vger.kernel.org

Do add me to CC as well. Before sending I'd recommend working out an
ip-netns based reproducer script -- makes it harder to ignore the report as
"ugh, too much work" ;)

Let me know if you need help with that,
--Daniel