Message-ID: <1450038035.3944.2.camel@decadent.org.uk>
Subject: Re: [PATCH 3.16.y-ckt 009/126] sit: fix sit0 percpu double
 allocations
From: Ben Hutchings <ben@decadent.org.uk>
To: Luis Henriques <luis.henriques@canonical.com>
Cc: Eric Dumazet <edumazet@google.com>,
        Steffen Klassert <steffen.klassert@secunet.com>,
        "David S. Miller" <davem@davemloft.net>, linux-kernel@vger.kernel.org,
        stable@vger.kernel.org, kernel-team@lists.ubuntu.com
Date: Sun, 13 Dec 2015 20:20:35 +0000
In-Reply-To: <20151213185429.GA31826@charon>
References: <1449653896-5236-1-git-send-email-luis.henriques@canonical.com>
	 <1449653896-5236-10-git-send-email-luis.henriques@canonical.com>
	 <1449893906.3836.5.camel@decadent.org.uk> <20151213185429.GA31826@charon>
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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.=C2=A0=C2=A0If anyone has any objec=
tions,
> > > please let me know.
> > >=20
> > > ------------------
> > >=20
> > > From: Eric Dumazet <edumazet@google.com>
> > >=20
> > > commit 4ece9009774596ee3df0acba65a324b7ea79387c upstream.
> > >=20
> > > sit0 device allocates its percpu storage twice :
> > > - One time in ipip6_tunnel_init()
> > > - One time in ipip6_fb_tunnel_init()
> > >=20
> > > Thus we leak 48 bytes per possible cpu per network namespace
> > > dismantle.
> > >=20
> > > ipip6_fb_tunnel_init() can be much simpler and does not
> > > return an error, and should be called after register_netdev()
> > [...]
> >=20
> > Doesn't this introduce a race condition when sit is a module? =C2=A0The=
re
> > 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.
> >=20
>=20
> This seems to be an upstream issue, not specific to the 3.16.y-ckt
> stable kernel.=C2=A0=C2=A0If that is the case, I guess I'll just keep thi=
s patch
> and later apply the fix.=C2=A0=C2=A0Or do you think this race is really l=
ikely
> to be a worst problem than then issue the patch is trying to fix?

It seems worse than the problem being fixed.

Ben.

--=20
Ben Hutchings
Life would be so much easier if we could look at the source code.
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