Subject: Re: [PATCH net-next v4] selftests: net: add tests for PPP

From: Guillaume Nault <[email-masked]>
Date: Fri, 27 Mar 2026 12:28:30 +0100

On Thu, Mar 26, 2026 at 04:26:23PM +0800, Qingfang Deng wrote:
> Hi Sebastian,
> 
> On Thu, Mar 26, 2026 at 4:13 PM Sebastian Andrzej Siewior
> <[email-masked]> wrote:
> >
> > On 2026-03-26 10:16:24 [+0800], Qingfang Deng wrote:
> > > Add ping and iperf3 tests for ppp_async.c and pppoe.c.
> >
> > Oh thank you for doing this.
> > I haven't look in detail but this cover the "invalid loop" cases that
> > ppp tries to catch?
> 
> By "invalid loop", do you mean transmit recursion?
> https://lore.kernel.org/all/[email-masked]/
> 
> AFAIK, this can only happen with PPTP or L2TP, which were not included
> in this patch.

The problem was originally reproduced using L2TP, indeed. But I guess
that it could also be reproduced with PPPoE by using a UDP tunnel
device like VXLAN (like sending a packet through a PPP interface,
handled by PPPoE, running on top of a VXLAN device, that routes the UDP
encapsulated packet back to the original PPP interface).

> Add Cc: Guillaume Nault
> Regards,
> Qingfang