netdev - Re: [PATCH net] l2tp: fix missing refcount drop in pppol2tp_tunnel

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Message-ID: <20180810175837.GB1430@alphalink.fr>
Date:   Fri, 10 Aug 2018 19:58:38 +0200
From:   Guillaume Nault <g.nault@...halink.fr>
To:     David Miller <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, jchapman@...alix.com
Subject: Re: [PATCH net] l2tp: fix missing refcount drop in
 pppol2tp_tunnel_ioctl()

On Sun, Aug 05, 2018 at 01:24:13PM +0200, Guillaume Nault wrote:
> On Fri, Aug 03, 2018 at 12:42:22PM -0700, David Miller wrote:
> > From: Guillaume Nault <g.nault@...halink.fr>
> > Date: Fri, 3 Aug 2018 17:00:11 +0200
> > 
> > > If 'session' is not NULL and is not a PPP pseudo-wire, then we fail to
> > > drop the reference taken by l2tp_session_get().
> > > 
> > > Fixes: ecd012e45ab5 ("l2tp: filter out non-PPP sessions in pppol2tp_tunnel_ioctl()")
> > > Signed-off-by: Guillaume Nault <g.nault@...halink.fr>
> > > ---
> > > Sorry for the stupid mistake. I guess I got blinded by the apparent
> > > simplicity of the bug when I wrote the original patch.
> > 
> > Applied, thanks.
> > 
> > I'm pretty sure I backported the commit this fixes, so I'm queueing
> > this up for -stable as well.
> > 
> Well, I think it wasn't. I didn't receive any notification from the
> stable team about it and I don't see it in Greg's stable queue nor
> in any -stable tree.
> 
> Also, we'd have to queue 90904ff5f958 ("l2tp: fix pseudo-wire type for
> sessions created by pppol2tp_connect()") first, which is necessary for
> properly identifying PPP sessions.
> 
> To recapitulate, three patches are needed to fix the original bug:
> 
>   * 90904ff5f958 ("l2tp: fix pseudo-wire type for sessions created by
>     pppol2tp_connect()"): allows later patches to check if a session is
>     PPP.
> 
>   * ecd012e45ab5 ("l2tp: filter out non-PPP sessions in
>     pppol2tp_tunnel_ioctl()"): refuses calling pppol2tp_session_ioctl()
>     on non-PPP sessions. This fixes an invalid pointer dereference when
>     the session is Ethernet. Unfortunately it fails to drop the
>     reference it takes on the session.
> 
>   * f664e37dcc52 ("l2tp: fix missing refcount drop in
>     pppol2tp_tunnel_ioctl()"): fixes the memory leak introduced by the
>     previous patch.
> 
Hi Dave,

As far as I can see, f664e37dcc52 ("l2tp: fix missing refcount drop in
pppol2tp_tunnel_ioctl()") is still in your -stable queue, but the two
patches it depends on haven't made their way to -stable. I'd suggest to
either drop this patch from your -stable queue, or to also queue up
ecd012e45ab5 ("l2tp: filter out non-PPP sessions in pppol2tp_tunnel_ioctl()")
and
f664e37dcc52 ("l2tp: fix missing refcount drop in pppol2tp_tunnel_ioctl()").