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Date:   Wed, 1 May 2019 11:27:12 +0200
From:   Matteo Croce <>
To:     Cong Wang <>,
        Vlad Buslov <>
Cc:     Linux Kernel Network Developers <>,
        LKML <>,
        Jamal Hadi Salim <>,
        Jiri Pirko <>,
        "David S. Miller" <>
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 <> wrote:
> On Mon, Apr 29, 2019 at 10:38 AM Matteo Croce <> 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.


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 <>
Date:   Mon Feb 11 10:55:38 2019 +0200

    net: sched: protect filter_chain list with filter_chain_lock mutex

Matteo Croce
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