netdev - Re: [Patch net] ppp: defer netns reference release for ppp channel

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Date:	Fri, 08 Jul 2016 23:47:54 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	xiyou.wangcong@...il.com
Cc:	netdev@...r.kernel.org, Matt.Bennett@...iedtelesis.co.nz,
	paulus@...ba.org, linux-ppp@...r.kernel.org, g.nault@...halink.fr,
	gorcunov@...nvz.org
Subject: Re: [Patch net] ppp: defer netns reference release for ppp channel

From: Cong Wang <xiyou.wangcong@...il.com>
Date: Tue,  5 Jul 2016 22:12:36 -0700

> Matt reported that we have a NULL pointer dereference
> in ppp_pernet() from ppp_connect_channel(),
> i.e. pch->chan_net is NULL.
> 
> This is due to that a parallel ppp_unregister_channel()
> could happen while we are in ppp_connect_channel(), during
> which pch->chan_net set to NULL. Since we need a reference
> to net per channel, it makes sense to sync the refcnt
> with the life time of the channel, therefore we should
> release this reference when we destroy it.
> 
> Fixes: 1f461dcdd296 ("ppp: take reference on channels netns")
> Reported-by: Matt Bennett <Matt.Bennett@...iedtelesis.co.nz>
> Cc: Paul Mackerras <paulus@...ba.org>
> Cc: linux-ppp@...r.kernel.org
> Cc: Guillaume Nault <g.nault@...halink.fr>
> Cc: Cyrill Gorcunov <gorcunov@...nvz.org>
> Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>

Applied and queued up for -stable.