netdev - Re: [PATCH net-next 2/2] net: sched: protect against stack overflow in TC act

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Message-ID: <4a4f2f81-d87a-2a45-36b9-ac101d937219@mojatatu.com>
Date:   Tue, 25 Jun 2019 07:24:37 -0400
From:   Jamal Hadi Salim <jhs@...atatu.com>
To:     John Hurley <john.hurley@...ronome.com>,
        Eyal Birger <eyal.birger@...il.com>
Cc:     Linux Netdev List <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Florian Westphal <fw@...len.de>,
        Simon Horman <simon.horman@...ronome.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        oss-drivers@...ronome.com, shmulik@...anetworks.com
Subject: Re: [PATCH net-next 2/2] net: sched: protect against stack overflow
 in TC act_mirred

On 2019-06-25 5:06 a.m., John Hurley wrote:
> On Tue, Jun 25, 2019 at 9:30 AM Eyal Birger <eyal.birger@...il.com> wrote:

> I'm not sure on the history of why a value of 4 was selected here but
> it seems to fall into line with my findings.

Back then we could only loop in one direction (as opposed to two right
now) - so seeing something twice would have been suspect enough,
so 4 seems to be a good number. I still think 4 is a good number.

> Is there a hard requirement for >4 recursive calls here?

I think this is where testcases help (which then get permanently
added in tdc repository). Eyal - if you have a test scenario where
this could be demonstrated it would help.

cheers,
jamal