netdev - Re: [PATCH net] net/sched: properly init chain in case of multiple control actions

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Date:   Sun, 14 Oct 2018 16:14:44 +0200
From:   Davide Caratti <dcaratti@...hat.com>
To:     Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>
Cc:     Jiri Pirko <jiri@...nulli.us>, David Miller <davem@...emloft.net>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH net] net/sched: properly init chain in case of multiple
 control actions

On Sun, 2018-10-14 at 09:46 -0400, Jamal Hadi Salim wrote:
> On 2018-10-13 11:23 a.m., Davide Caratti wrote:
> > 
> > A (legal?) trick  is to let tcf_action store the fallback action when it
> > contains a 'goto chain' command, I just posted a proposal for gact. If you
> > think it's ok, I will test and post the same for act_police.
> > 
> 
> Need some more thought. So the issue here is the goto chain failed
> the configured chain doesnt exist?

'goto chain' works only if it's stored in tcfa_action: if not, it does
NULL  dereference. That's ok for most actions, but not for gact and police
- as they allow two control actions simultaneously, and the one that is
stored in the action-specific data does not initialize any chain (because
the initialization of 'goto_chain' data is done at [1])

(while at it, I also checked act_bpf, and it seems ok because 'goto chain'
does not seem to be a valid control action for eBPF programs.)

regards,
-- 
davide

[1] https://elixir.bootlin.com/linux/v4.19-rc7/source/net/sched/act_api.c#L888