netdev - Re: [PATCH net] ppp: ensure file->private

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Message-ID: <20160314190928.GR1186@alphalink.fr>
Date:	Mon, 14 Mar 2016 20:09:28 +0100
From:	Guillaume Nault <g.nault@...halink.fr>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org, paulus@...ba.org, alan@...ux.intel.com,
	arnd@...db.de
Subject: Re: [PATCH net] ppp: ensure file->private_data can't be overridden

On Mon, Mar 14, 2016 at 02:57:59PM -0400, David Miller wrote:
> From: Guillaume Nault <g.nault@...halink.fr>
> Date: Mon, 14 Mar 2016 18:59:40 +0100
> 
> > Testing ->private_data without lock in ppp_ioctl() before calling
> > ppp_unattached_ioctl() is fine, because either ->private_data is
> > not NULL and thus is stable, or it is and ppp_unattached_ioctl()
> > takes care of not overriding ->private_data, should its value get
> > modified before taking the mutex.
> 
> This is exactly the ambiguous behavior I want you to avoid.
> 
> The decision should be atomic from ppp_ioctl()'s test all the way
> until ppp_unattached_ioctl() does it's work.

OK, will fix in v2.