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

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Message-ID: <20160204130510.GD1267@alphalink.fr>
Date:	Thu, 4 Feb 2016 14:05:10 +0100
From:	Guillaume Nault <g.nault@...halink.fr>
To:	Sorin Manolache <sorinm@...il.com>
Cc:	netdev@...r.kernel.org,
	Stephen Hemminger <stephen@...workplumber.org>
Subject: Re: Fw: [Bug 111771] New: deadlock in ppp/l2tp

On Thu, Feb 04, 2016 at 02:32:48AM +0100, Sorin Manolache wrote:
> On 2016-02-03 18:14, Guillaume Nault wrote:
> > 
> >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?
> 
If that's a /32 IPv4 route to the peer address of the PPP link and has
the "proto kernel" attribute, then yes, that's most likely the one
generated by the kernel.