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

[Emeel Hakim <ehakim@nvidia.com>]

> -----Original Message-----
> From: Antoine Tenart <atenart@kernel.org>
> Sent: Tuesday, 10 January 2023 10:44
> To: Sabrina Dubroca <sd@queasysnail.net>; Emeel Hakim <ehakim@nvidia.com>
> Cc: netdev@vger.kernel.org; Raed Salem <raeds@nvidia.com>;
> davem@davemloft.net; edumazet@google.com; kuba@kernel.org;
> pabeni@redhat.com
> Subject: Re: [PATCH net-next v7 1/2] macsec: add support for
> IFLA_MACSEC_OFFLOAD in macsec_changelink
> 
> External email: Use caution opening links or attachments
> 
> 
> Quoting Sabrina Dubroca (2023-01-09 16:14:32)
> > 2023-01-09, 10:55:56 +0200, ehakim@nvidia.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:

Ack , I can do the change

>   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.

why do we need to restore offloading state here in case of failure?
we get to this case when prev_offload == offload.

>   }
> 
> Thanks,
> Antoine