On Tue, Jun 01, 2021 at 03:35:10PM +0300, Boris Sukholitko wrote:
> Hi Jacub,
>
> On Mon, May 31, 2021 at 10:21:36PM -0700, Jakub Kicinski wrote:
> > On Sun, 30 May 2021 14:40:51 +0300 Boris Sukholitko wrote:
> > > diff --git a/net/sched/act_vlan.c b/net/sched/act_vlan.c
[...]
> > > @@ -362,10 +362,19 @@ static int tcf_vlan_search(struct net *net, struct tc_action **a, u32 index)
> > >
> > > static size_t tcf_vlan_get_fill_size(const struct tc_action *act)
> > > {
> > > - return nla_total_size(sizeof(struct tc_vlan))
> > > + struct tcf_vlan *v = to_vlan(act);
> > > + struct tcf_vlan_params *p;
> > > + size_t ret = nla_total_size(sizeof(struct tc_vlan))
> > > + nla_total_size(sizeof(u16)) /* TCA_VLAN_PUSH_VLAN_ID */
> > > - + nla_total_size(sizeof(u16)) /* TCA_VLAN_PUSH_VLAN_PROTOCOL */
> > > - + nla_total_size(sizeof(u8)); /* TCA_VLAN_PUSH_VLAN_PRIORITY */
> > > + + nla_total_size(sizeof(u16)); /* TCA_VLAN_PUSH_VLAN_PROTOCOL */
> > > +
> > > + spin_lock_bh(&v->tcf_lock);
> > > + p = rcu_dereference_protected(v->vlan_p, lockdep_is_held(&v->tcf_lock));
> > > + if (p->tcfv_push_prio_exists)
> > > + ret += nla_total_size(sizeof(u8)); /* TCA_VLAN_PUSH_VLAN_PRIORITY */
> > > + spin_unlock_bh(&v->tcf_lock);
> >
> > This jumps out a little bit - if we need to take this lock to inspect
> > tcf_vlan_params, then I infer its value may change. And if it may
> > change what guarantees it doesn't change between calculating the skb
> > length and dumping?
> >
> > It's common practice to calculate the max skb len required when
> > attributes are this small.
> >
>
> I believe you are right.
ouch, that's my fault actually - it's true, TC rules can be
modified and dumped at the same time. Then the only thing we can
do is to account for TCA_VLAN_PUSH_VLAN_PRIORITY even if we will not
fill it.
thanks for spotting this,
--
davide
