Re: [PATCH net] net: flow_offload: skip hw stats check for FLOW_ACTION_HW_STATS_DISABLED

Pablo Neira Ayuso
2020-04-20T10:03:46Z

On Mon, Apr 20, 2020 at 11:13:02AM +0200, Jiri Pirko wrote:
> Mon, Apr 20, 2020 at 11:05:05AM CEST, pablo@netfilter.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@netfilter.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!