netdev - Re: [PATCH net] cls_matchall: avoid panic when receiving a packet before filter set

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Message-ID: <CAGnkfhzPZjqnemq+Sh=pAQPsoadYD2UYfdVf8UHt-Dd7gqhVOg@mail.gmail.com>
Date:   Wed, 1 May 2019 11:27:12 +0200
From:   Matteo Croce <mcroce@...hat.com>
To:     Cong Wang <xiyou.wangcong@...il.com>,
        Vlad Buslov <vladbu@...lanox.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Jiri Pirko <jiri@...nulli.us>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH net] cls_matchall: avoid panic when receiving a packet
 before filter set

On Tue, Apr 30, 2019 at 11:25 PM Cong Wang <xiyou.wangcong@...il.com> wrote:
>
> On Mon, Apr 29, 2019 at 10:38 AM Matteo Croce <mcroce@...hat.com> wrote:
> >
> > When a matchall classifier is added, there is a small time interval in
> > which tp->root is NULL. If we receive a packet in this small time slice
> > a NULL pointer dereference will happen, leading to a kernel panic:
>
> Hmm, why not just check tp->root against NULL in mall_classify()?
>
> Also, which is the offending commit here? Please add a Fixes: tag.
>
> Thanks.

Hi,

I just want to avoid an extra check which would be made for every packet.
Probably the benefit over a check is negligible, but it's still a
per-packet thing.
If you prefer a simple check, I can make a v2 that way.

For the fixes tag, I didn't put it as I'm not really sure about the
offending commit. I guess it's the following, what do you think?

commit ed76f5edccc98fa66f2337f0b3b255d6e1a568b7
Author: Vlad Buslov <vladbu@...lanox.com>
Date:   Mon Feb 11 10:55:38 2019 +0200

    net: sched: protect filter_chain list with filter_chain_lock mutex

-- 
Matteo Croce
per aspera ad upstream