linux-kernel - Re: [PATCH net-next] net: ethtool: Fix suspicious rcu

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Message-ID: <20241218100756.30de216b@kmaincent-XPS-13-7390>
Date: Wed, 18 Dec 2024 10:07:56 +0100
From: Kory Maincent <kory.maincent@...tlin.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org,
 syzbot+a344326c05c98ba19682@...kaller.appspotmail.com,
 thomas.petazzoni@...tlin.com, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
 <pabeni@...hat.com>, Simon Horman <horms@...nel.org>
Subject: Re: [PATCH net-next] net: ethtool: Fix suspicious rcu_dereference
 usage

On Tue, 17 Dec 2024 18:28:16 +0100
Eric Dumazet <edumazet@...gle.com> wrote:

> On Tue, Dec 17, 2024 at 6:17 PM Kory Maincent <kory.maincent@...tlin.com>
> wrote:
> >
> > On Tue, 17 Dec 2024 16:47:07 +0100
> > Eric Dumazet <edumazet@...gle.com> wrote:
> >  
> > > On Tue, Dec 17, 2024 at 3:03 PM Kory Maincent <kory.maincent@...tlin.com>
> > > wrote:  
>  [...]  
> > >
> > > I have to ask : Can you tell how this patch has been tested ?  
> >
> > Oh, it was not at all sufficiently tested. Sorry!
> > I thought I had spotted the issue but I hadn't.
> >  
> > > rcu is not held according to syzbot report.
> > >
> > > If rtnl and rcu are not held, lockdep will still complain.  
> >
> > You are totally right.
> > I may be able to see it with the timestamping kselftest. I will try.  
> 
> syzbot has a repro that you can compile and run.

Oh indeed, thanks for the pointer.

> Make sure to build and use a kernel with
> 
> CONFIG_PROVE_LOCKING=y

Yes I did.

Regards,
-- 
Köry Maincent, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com