netdev - Re: [PATCH RESEND] ipconfig : Fix null reference to the freed dev

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Date:	Sun, 26 Jun 2016 15:43:46 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	chanho.min@....com
Cc:	netdev@...r.kernel.org, kuznet@....inr.ac.ru, jmorris@...ei.org,
	fabf@...net.be, gunho.lee@....com, linux-kernel@...r.kernel.org,
	neidhard.kim@....com
Subject: Re: [PATCH RESEND] ipconfig : Fix null reference to the freed
 dev_addr

From: Chanho Min <chanho.min@....com>
Date: Wed, 22 Jun 2016 19:08:13 +0900

> To fix this, I suggested patch that checks if device is available
> before the DHCP packet is sended.

The bug is more fundamental than this.

The code is not taking a reference to the netdevice, and that's
the only reason it is able to disappear like this.

It is illegal to reference a netdevice after dropping the rtnl
mutex unless you take a proper reference to it.