netdev - Re: [PATCH net] net: flow_offload: skip hw stats check for FLOW_ACTION_HW_STATS

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Date:   Mon, 20 Apr 2020 12:03:41 +0200
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     Jiri Pirko <jiri@...nulli.us>
Cc:     netfilter-devel@...r.kernel.org, davem@...emloft.net,
        netdev@...r.kernel.org, kuba@...nel.org
Subject: Re: [PATCH net] net: flow_offload: skip hw stats check for
 FLOW_ACTION_HW_STATS_DISABLED

On Mon, Apr 20, 2020 at 11:13:02AM +0200, Jiri Pirko wrote:
> Mon, Apr 20, 2020 at 11:05:05AM CEST, pablo@...filter.org wrote:
> >On Mon, Apr 20, 2020 at 10:02:00AM +0200, Jiri Pirko wrote:
> >> Sun, Apr 19, 2020 at 01:53:38PM CEST, pablo@...filter.org wrote:
> >> >If the frontend requests no stats through FLOW_ACTION_HW_STATS_DISABLED,
> >> >drivers that are checking for the hw stats configuration bail out with
> >> >EOPNOTSUPP.
> >>
> >> Wait, that was a point. Driver has to support stats disabling.
> >
> >Hm, some drivers used to accept FLOW_ACTION_HW_STATS_DISABLED, now
> >rulesets that used to work don't work anymore.
>
> How? This check is here since the introduction of hw stats types.

Netfilter is setting the counter support to
FLOW_ACTION_HW_STATS_DISABLED in this example below:

  table netdev filter {
        chain ingress {
                type filter hook ingress device eth0 priority 0; flags offload;

                tcp dport 22 drop
        }
  }

The user did not specify a counter in this case.

I think __flow_action_hw_stats_check() cannot work with
FLOW_ACTION_HW_STATS_DISABLED.

If check_allow_bit is false and FLOW_ACTION_HW_STATS_DISABLED is
specified, then this always evaluates true:

        if (!check_allow_bit &&
            action_entry->hw_stats != FLOW_ACTION_HW_STATS_ANY) {

Similarly:

        } else if (check_allow_bit &&
                   !(action_entry->hw_stats & BIT(allow_bit))) {

evaluates true for FLOW_ACTION_HW_STATS_DISABLED, assuming allow_bit is
set, which I think it is the intention.

Another suggestion: This is control plane code and this
__flow_action_hw_stats_check() function is relatively large, I'd suggest
to move it to net/core/flow_offload.c at some point.

Thank you!