From: Jon Maloy <jon.maloy@ericsson.com>
To: Tommi Rantala <tommi.t.rantala@nokia.com>,
        Ying Xue <ying.xue@windriver.com>,
        "David S. Miller" <davem@davemloft.net>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "tipc-discussion@lists.sourceforge.net" 
        <tipc-discussion@lists.sourceforge.net>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH net v2] tipc: call tipc_rcv() only if bearer is up in
 tipc_udp_recv()
Thread-Topic: [PATCH net v2] tipc: call tipc_rcv() only if bearer is up in
 tipc_udp_recv()
Thread-Index: AQHTaQAHc0u3EIYoAUSeGeIO/vyPGqMswf4AgAAalQCAAZ9IgIAADEaAgAADrMA=
Date: Fri, 1 Dec 2017 14:20:49 +0000
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References: <20171129104842.30781-1-tommi.t.rantala@nokia.com>
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 <840ce8d1-7271-5189-4cfa-e40f4a0a4172@windriver.com>
 <c110a0a9-4092-19aa-7d09-99e38d161663@nokia.com>
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Looks ok to me too. But I suggest we let David apply the pending patch as is to net, as that code is still wrong, and then post this improvement to net-next later.

///jon


> -----Original Message-----
> From: Tommi Rantala [mailto:tommi.t.rantala@nokia.com]
> Sent: Friday, December 01, 2017 09:03
> To: Ying Xue <ying.xue@windriver.com>; Jon Maloy
> <jon.maloy@ericsson.com>; David S. Miller <davem@davemloft.net>;
> netdev@vger.kernel.org; tipc-discussion@lists.sourceforge.net; linux-
> kernel@vger.kernel.org
> Subject: Re: [PATCH net v2] tipc: call tipc_rcv() only if bearer is up in
> tipc_udp_recv()
> 
> On 01.12.2017 15:18, Ying Xue wrote:
> > On 11/30/2017 08:32 PM, Tommi Rantala wrote:
> >>> In my opinion, the real root cause of the issue is because we too
> >>> early set a not-yet-initialized bearer instance to ub->bearer
> >>> through rcu_assign_pointer(ub->bearer, b) in tipc_udp_enable().
> >>> Instead if we assign the bearer pointer at the end of
> >>> tipc_udp_enable() where the bearer has been completed the
> initialization, the issue would be avoided.
> >> Hi, sorry, I fail to see how that helps.
> >>
> >> bearer->tolerance is only initialized in tipc_enable_bearer() after
> >> calling m->enable_media() ie. tipc_udp_enable().
> >>
> >> So even if we do "rcu_assign_pointer(ub->bearer, b)" later in
> >> tipc_udp_enable(), bearer->tolerance will still be uninitialized, and
> >> the crash can happen.
> >
> > Sorry, I missed the point that b->tolerance is not uninitialized when
> > we assign bearer pointer to ub->bearer later.
> >
> > But in my view the issue happened is because we enable media too early.
> > So it's better to change the code as belows:
> 
> Thanks, looks good to me!
> 
> Tested in 4.4 (which does not have b->up), and this fixes the oops also there.
> 
> -Tommi
> 
> 
> > diff --git a/net/tipc/bearer.c b/net/tipc/bearer.c index
> > 47ec121..ec6f02a 100644
> > --- a/net/tipc/bearer.c
> > +++ b/net/tipc/bearer.c
> > @@ -320,19 +320,18 @@ static int tipc_enable_bearer(struct net *net,
> > const char *name,
> >
> >          strcpy(b->name, name);
> >          b->media = m;
> > -       res = m->enable_media(net, b, attr);
> > -       if (res) {
> > -               pr_warn("Bearer <%s> rejected, enable failure (%d)\n",
> > -                       name, -res);
> > -               return -EINVAL;
> > -       }
> > -
> >          b->identity = bearer_id;
> >          b->tolerance = m->tolerance;
> >          b->window = m->window;
> >          b->domain = disc_domain;
> >          b->net_plane = bearer_id + 'A';
> >          b->priority = priority;
> > +       res = m->enable_media(net, b, attr);
> > +       if (res) {
> > +               pr_warn("Bearer <%s> rejected, enable failure (%d)\n",
> > +                       name, -res);
> > +               return -EINVAL;
> > +       }
> >          test_and_set_bit_lock(0, &b->up);
> >