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

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Date:	Sun, 13 Dec 2015 18:54:29 +0000
From:	Luis Henriques <luis.henriques@...onical.com>
To:	Ben Hutchings <ben@...adent.org.uk>
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 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?

Cheers,
--
Luís

> Ben.
> 
> -- 
> Ben Hutchings
> Knowledge is power.  France is bacon.

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