netdev - Re: Fw: [Bug 111771] New: deadlock in ppp/l2tp

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Message-ID: <56B2AA40.5090601@gmail.com>
Date:	Thu, 4 Feb 2016 02:32:48 +0100
From:	Sorin Manolache <sorinm@...il.com>
To:	Guillaume Nault <g.nault@...halink.fr>
Cc:	netdev@...r.kernel.org,
	Stephen Hemminger <stephen@...workplumber.org>
Subject: Re: Fw: [Bug 111771] New: deadlock in ppp/l2tp

On 2016-02-03 18:14, Guillaume Nault wrote:
> On Wed, Feb 03, 2016 at 11:04:31AM +1100, Stephen Hemminger wrote:
>> Please excuse URL mangling, my bugzilla address appears to route through
>> stupid corporate firewall.
>>
>
> Sorin, it seems like one of your L2TP tunnels is routed to one of its upper PPP
> devices. Most likely, the peer address of the PPP device is also the address of
> the remote L2TP tunnel endpoint. So L2TP packets are sent back to the upper PPP
> device, instead of leaving through the physical interface.

Thank you. You are right. There's a host route to the peer over the ppp0 
interface in the routing table. I don't know how it gets there. I've 
checked the source code of pppd and no such route is added for kernels 
newer than 2.1.16. I've grepped /etc for "route" in order to detect a 
"post-up" script that would add that route. Nothing. I've double-checked 
by executing strace on xl2tpd and its children (i.e. pppd and the 
initialisation scripts) and I couldn't find any ioctl SIOCADDRT. So it's 
a total mystery for me where that route comes from. Could it come from 
the kernel?

I've found this 9-year-old bug report: 
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=444180. I've adopted 
the strategy that the comment proposes: delete the route in an post-up 
script.

Thanks again.

Best regards,
Sorin