netdev - Re: [PATCH 2/7] mark root hnode explicitly

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Date:   Fri, 7 Sep 2018 04:04:38 +0100
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     Jamal Hadi Salim <jhs@...atatu.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Jiri Pirko <jiri@...nulli.us>
Subject: Re: [PATCH 2/7] mark root hnode explicitly

On Thu, Sep 06, 2018 at 07:57:25PM -0700, Cong Wang wrote:

> > -       if (root_ht == ht) {
> > +       if (ht->is_root) {
> 
> 
> What's wrong with comparing pointers with root ht?

The fact that there may be more than one tcf_proto sharing tp->data.

> >                 NL_SET_ERR_MSG_MOD(extack, "Not allowed to delete root node");
> >                 return -EINVAL;
> >         }
> > @@ -795,6 +797,10 @@ static int u32_set_parms(struct net *net, struct tcf_proto *tp,
> >                                 NL_SET_ERR_MSG_MOD(extack, "Link hash table not found");
> >                                 return -EINVAL;
> >                         }
> > +                       if (ht_down->is_root) {
> 
> root ht is saved in tp->root, so you can compare ht_down with it too,
> if you want.
> 
> If this check is all what you need, you don't need an extra flag.

Again, *which* tp?  We can trivially check that we are not linking to/deleting
our own root, sure.  But there's nothing to stop doing the same via another
tcf_proto...