netdev - Re: [net-next v3 1/6] net: dcb: add new pcp selector to app object

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Date:   Wed, 26 Oct 2022 11:19:26 +0000
From:   <Daniel.Machon@...rochip.com>
To:     <petrm@...dia.com>
CC:     <netdev@...r.kernel.org>, <davem@...emloft.net>,
        <maxime.chevallier@...tlin.com>, <thomas.petazzoni@...tlin.com>,
        <edumazet@...gle.com>, <kuba@...nel.org>, <pabeni@...hat.com>,
        <Lars.Povlsen@...rochip.com>, <Steen.Hegelund@...rochip.com>,
        <UNGLinuxDriver@...rochip.com>, <joe@...ches.com>,
        <linux@...linux.org.uk>, <Horatiu.Vultur@...rochip.com>,
        <Julia.Lawall@...ia.fr>, <vladimir.oltean@....com>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [net-next v3 1/6] net: dcb: add new pcp selector to app object

> > Add new PCP selector for the 8021Qaz APP managed object.
> >
> > As the PCP selector is not part of the 8021Qaz standard, a new non-std
> > extension attribute DCB_ATTR_DCB_APP has been introduced. Also two
> > helper functions to translate between selector and app attribute type
> > has been added. The new selector has been given a value of 255, to
> > minimize the risk of future overlap of std- and non-std attributes.
> >
> > The new DCB_ATTR_DCB_APP is sent alongside the ieee std attribute in the
> > app table. This means that the dcb_app struct can now both contain std-
> > and non-std app attributes. Currently there is no overlap between the
> > selector values of the two attributes.
> >
> > The purpose of adding the PCP selector, is to be able to offload
> > PCP-based queue classification to the 8021Q Priority Code Point table,
> > see 6.9.3 of IEEE Std 802.1Q-2018.
> >
> > PCP and DEI is encoded in the protocol field as 8*dei+pcp, so that a
> > mapping of PCP 2 and DEI 1 to priority 3 is encoded as {255, 10, 3}.
> >
> > Signed-off-by: Daniel Machon <daniel.machon@...rochip.com>
> 
> >  static struct sk_buff *dcbnl_newmsg(int type, u8 cmd, u32 port, u32 seq,
> >                                   u32 flags, struct nlmsghdr **nlhp)
> >  {
> > @@ -1116,8 +1143,9 @@ static int dcbnl_ieee_fill(struct sk_buff *skb, struct net_device *netdev)
> >       spin_lock_bh(&dcb_lock);
> >       list_for_each_entry(itr, &dcb_app_list, list) {
> >               if (itr->ifindex == netdev->ifindex) {
> > -                     err = nla_put(skb, DCB_ATTR_IEEE_APP, sizeof(itr->app),
> > -                                      &itr->app);
> > +                     enum ieee_attrs_app type =
> > +                             dcbnl_app_attr_type_get(itr->app.selector);
> > +                     err = nla_put(skb, type, sizeof(itr->app), &itr->app);
> >                       if (err) {
> >                               spin_unlock_bh(&dcb_lock);
> >                               return -EMSGSIZE;
> > @@ -1495,7 +1523,7 @@ static int dcbnl_ieee_set(struct net_device *netdev, struct nlmsghdr *nlh,
> >               nla_for_each_nested(attr, ieee[DCB_ATTR_IEEE_APP_TABLE], rem) {
> >                       struct dcb_app *app_data;
> >
> > -                     if (nla_type(attr) != DCB_ATTR_IEEE_APP)
> > +                     if (!dcbnl_app_attr_type_validate(nla_type(attr)))
> >                               continue;
> >
> >                       if (nla_len(attr) < sizeof(struct dcb_app)) {
> > @@ -1556,7 +1584,7 @@ static int dcbnl_ieee_del(struct net_device *netdev, struct nlmsghdr *nlh,
> >               nla_for_each_nested(attr, ieee[DCB_ATTR_IEEE_APP_TABLE], rem) {
> >                       struct dcb_app *app_data;
> >
> > -                     if (nla_type(attr) != DCB_ATTR_IEEE_APP)
> > +                     if (!dcbnl_app_attr_type_validate(nla_type(attr)))
> >                               continue;
> >                       app_data = nla_data(attr);
> >                       if (ops->ieee_delapp)
> 
> I'm missing a validation that DCB_APP_SEL_PCP is always sent in
> DCB_ATTR_DCB_APP encapsulation. Wouldn't the current code permit
> sending it in the IEEE encap? This should be forbidden.

Right. Current impl. does not check that the non-std selectors received, are
sent with a DCB_ATTR_DCB_APP type.  We could introduce a new check
dcbnl_app_attr_selector_validate() that checks combination of type and 
selector, after the type and nla_len(attr) has been checked, so that:

 validate type -> validate nla_len(attr) -> validate selector

> And vice versa: I'm not sure we want to permit sending the standard
> attributes in the DCB encap.

dcbnl_app_attr_type_get() in dcbnl_ieee_fill() takes care of this. IEEE are
always sent in DCB_ATTR_IEEE and non-std are sent in DCB_ATTR_DCB.

/ Daniel