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
> > index a108469c664f..ccd1acfa4c55 100644
> > --- a/net/sched/act_vlan.c
> > +++ b/net/sched/act_vlan.c
> > @@ -307,8 +307,8 @@ static int tcf_vlan_dump(struct sk_buff *skb, struct tc_action *a,
> > (nla_put_u16(skb, TCA_VLAN_PUSH_VLAN_ID, p->tcfv_push_vid) ||
> > nla_put_be16(skb, TCA_VLAN_PUSH_VLAN_PROTOCOL,
> > p->tcfv_push_proto) ||
> > - (nla_put_u8(skb, TCA_VLAN_PUSH_VLAN_PRIORITY,
> > - p->tcfv_push_prio))))
> > + (p->tcfv_push_prio_exists &&
> > + nla_put_u8(skb, TCA_VLAN_PUSH_VLAN_PRIORITY, p->tcfv_push_prio))))
> > goto nla_put_failure;
> >
> > if (p->tcfv_action == TCA_VLAN_ACT_PUSH_ETH) {
> > @@ -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.
I've just sent out v4 of the patch with tcf_vlan_get_fill_size change
reverted.
Thanks,
Boris.
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