netdev - Re: [PATCH net] ppp: don't override sk->sk_state in pppoe_flush

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Message-ID: <20151005122459.GG2911@alphalink.fr>
Date:	Mon, 5 Oct 2015 14:24:59 +0200
From:	Guillaume Nault <g.nault@...halink.fr>
To:	Matt Bennett <Matt.Bennett@...iedtelesis.co.nz>
Cc:	"nuclearcat@...learcat.com" <nuclearcat@...learcat.com>,
	"core@....lg.ua" <core@....lg.ua>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"paulus@...ba.org" <paulus@...ba.org>
Subject: Re: [PATCH net] ppp: don't override sk->sk_state in pppoe_flush_dev()

On Mon, Oct 05, 2015 at 04:08:51AM +0000, Matt Bennett wrote:
> Hi, I am seeing this panic occur occasionally however I am unsure how to
> go about reproducing it. Is it enough to simply keep creating and
> tearing down the PPP interface? I can also test and/or investigate this
> issue if a suitable reproduction method is available.
> 
There are at least two issues resulting in similar Oops.

The first one goes with MTU/address/link state updates on the
underlying interface: any such update on an interface used by a
PPPoE connection will generally result in an Oops when releasing the
PPPoE connection. This is fixed by e6740165b8f7 ("ppp: don't override
sk->sk_state in pppoe_flush_dev()").

The second one seems to be trickier. It looks like a race wrt. PADT
message reception. Reproducing the bug will probably require to
generate some PADT flooding to a host that creates and releases PPPoE
connections.
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