linux-kernel - Re: [PATCH 3.16.y-ckt 009/126] sit: fix sit0 percpu double allocations

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Message-ID: <1450038035.3944.2.camel@decadent.org.uk>
Date:	Sun, 13 Dec 2015 20:20:35 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Luis Henriques <luis.henriques@...onical.com>
Cc:	Eric Dumazet <edumazet@...gle.com>,
	Steffen Klassert <steffen.klassert@...unet.com>,
	"David S. Miller" <davem@...emloft.net>,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Subject: Re: [PATCH 3.16.y-ckt 009/126] sit: fix sit0 percpu double
 allocations

On Sun, 2015-12-13 at 18:54 +0000, Luis Henriques wrote:
> On Sat, Dec 12, 2015 at 04:18:26AM +0000, Ben Hutchings wrote:
> > On Wed, 2015-12-09 at 09:36 +0000, Luis Henriques wrote:
> > > 3.16.7-ckt21 -stable review patch.  If anyone has any objections,
> > > please let me know.
> > > 
> > > ------------------
> > > 
> > > From: Eric Dumazet <edumazet@...gle.com>
> > > 
> > > commit 4ece9009774596ee3df0acba65a324b7ea79387c upstream.
> > > 
> > > sit0 device allocates its percpu storage twice :
> > > - One time in ipip6_tunnel_init()
> > > - One time in ipip6_fb_tunnel_init()
> > > 
> > > Thus we leak 48 bytes per possible cpu per network namespace
> > > dismantle.
> > > 
> > > ipip6_fb_tunnel_init() can be much simpler and does not
> > > return an error, and should be called after register_netdev()
> > [...]
> > 
> > Doesn't this introduce a race condition when sit is a module?  There
> > seems to be nothing to prevent access to the partially initialised
> > device after calling register_netdev(), if sit_init_net() is called
> > during module loading rather than during namespace creation.
> > 
> 
> This seems to be an upstream issue, not specific to the 3.16.y-ckt
> stable kernel.  If that is the case, I guess I'll just keep this patch
> and later apply the fix.  Or do you think this race is really likely
> to be a worst problem than then issue the patch is trying to fix?

It seems worse than the problem being fixed.

Ben.

-- 
Ben Hutchings
Life would be so much easier if we could look at the source code.
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