netdev - Re: [PATCH net-next v7 1/2] macsec: add support for IFLA_MACSEC_OFFLOAD in macsec

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Date:   Tue, 10 Jan 2023 09:43:37 +0100
From:   Antoine Tenart <atenart@...nel.org>
To:     Sabrina Dubroca <sd@...asysnail.net>, ehakim@...dia.com
Cc:     netdev@...r.kernel.org, raeds@...dia.com, davem@...emloft.net,
        edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com
Subject: Re: [PATCH net-next v7 1/2] macsec: add support for IFLA_MACSEC_OFFLOAD in macsec_changelink

Quoting Sabrina Dubroca (2023-01-09 16:14:32)
> 2023-01-09, 10:55:56 +0200, ehakim@...dia.com wrote:
> > @@ -3840,6 +3835,12 @@ static int macsec_changelink(struct net_device *dev, struct nlattr *tb[],
> >       if (ret)
> >               goto cleanup;
> >  
> > +     if (data[IFLA_MACSEC_OFFLOAD]) {
> > +             ret = macsec_update_offload(dev, nla_get_u8(data[IFLA_MACSEC_OFFLOAD]));
> > +             if (ret)
> > +                     goto cleanup;
> > +     }
> > +
> >       /* If h/w offloading is available, propagate to the device */
> >       if (macsec_is_offloaded(macsec)) {
> >               const struct macsec_ops *ops;
> 
> There's a missing rollback of the offloading status in the (probably
> quite unlikely) case that mdo_upd_secy fails, no? We can't fail
> macsec_get_ops because macsec_update_offload would have failed
> already, but I guess the driver could fail in mdo_upd_secy, and then
> "goto cleanup" doesn't restore the offloading state.  Sorry I didn't
> notice this earlier.
> 
> In case the IFLA_MACSEC_OFFLOAD attribute is provided and we're
> enabling offload, we also end up calling the driver's mdo_add_secy,
> and then immediately afterwards mdo_upd_secy, which probably doesn't
> make much sense.
> 
> Maybe we could turn that into:
> 
>     if (data[IFLA_MACSEC_OFFLOAD]) {

If data[IFLA_MACSEC_OFFLOAD] is provided but doesn't change the
offloading state, then macsec_update_offload will return early and
mdo_upd_secy won't be called.

>         ... macsec_update_offload
>     } else if (macsec_is_offloaded(macsec)) {
>         /* If h/w offloading is available, propagate to the device */
>         ... mdo_upd_secy
>     }
> 
> Antoine, does that look reasonable to you?

But yes I agree we can improve the logic. Maybe something like:

  prev_offload = macsec->offload;
  offload = data[IFLA_MACSEC_OFFLOAD];

  if (prev_offload != offload) {
      macsec_update_offload(...)
  } else if (macsec_is_offloaded(macsec)) {
      ...
      prev_offload can be used to restore the offloading state on
      failure here.
  }

Thanks,
Antoine