Re: [PATCH] net/sfc: cut non VLAN ID bits from TCI

[Adrien Mazarguil <adrien.mazarguil@6wind.com>]

On Thu, Jul 05, 2018 at 01:14:49PM +0200, Adrien Mazarguil wrote:
> On Fri, Jun 29, 2018 at 04:23:31PM +0100, Andrew Rybchenko wrote:
> > TCI may contain PCP or DEI bits. Matching of these bits is not
> > supported, but the bits still may be set in specification value and
> > not covered by mask. So, these bits should be ignored.
> > 
> > Fixes: 894080975e1e ("net/sfc: support VLAN in flow API filters")
> > Cc: stable@dpdk.org
> > 
> > Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>
> > Reviewed-by: Roman Zhukov <roman.zhukov@oktetlabs.ru>
> > 
> > ---
> >  drivers/net/sfc/sfc_flow.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/net/sfc/sfc_flow.c b/drivers/net/sfc/sfc_flow.c
> > index 5613d59a9..18387415e 100644
> > --- a/drivers/net/sfc/sfc_flow.c
> > +++ b/drivers/net/sfc/sfc_flow.c
> > @@ -371,7 +371,8 @@ sfc_flow_parse_vlan(const struct rte_flow_item *item,
> >  	 * the outer tag and the next matches the inner tag.
> >  	 */
> >  	if (mask->tci == supp_mask.tci) {
> > -		vid = rte_bswap16(spec->tci);
> > +		/* Apply mask to keep VID only */
> > +		vid = rte_bswap16(spec->tci & mask->tci);
> >  
> >  		if (!(efx_spec->efs_match_flags &
> >  		      EFX_FILTER_MATCH_OUTER_VID)) {
> 
> I think there is an issue with this patch when spec->mask is user-provided,
> PMDs have to trust it. They must not simply ignore bits they cannot handle
> but explicitly reject the flow rule for correctness.
> 
> Most devices cannot match PCP and DEI, this is why the default TCI mask was
> modified in v18.05 by commit 0730ab674cb1 ("ethdev: fix default VLAN TCI
> mask in flow API") to cover the VID part only.
> 
> I wrote a helper for mlx5 to help with such basic sanity checks on pattern
> items in a generic(ish) fashion, maybe you could reuse something. Have a
> look at mlx5_nl_flow_item_mask() [1].
> 
> [1] "net/mlx5: add L2-L4 pattern items to switch flow rules"
>     https://mails.dpdk.org/archives/dev/2018-June/105579.html

Seems like I misread the original patch and PMD code, both are in fact
correct.

Please ignore my previous comment, sorry for the noise!

-- 
Adrien Mazarguil
6WIND