On Mon, Sep 19, 2016 at 1:04 PM, Shmulik Ladkani
<shmulik.ladk...@gmail.com> wrote:
> Hi Pravin,
>
> On Sun, 18 Sep 2016 13:26:30 -0700 pravin shelar <pshe...@ovn.org> wrote:
>> > +++ b/net/core/skbuff.c
>> > @@ -4537,7 +4537,7 @@ int skb_vlan_pop(struct sk_buff *skb)
>> > } else {
>> > if (unlikely((skb->protocol != htons(ETH_P_8021Q) &&
>> > skb->protocol != htons(ETH_P_8021AD)) ||
>> > - skb->len < VLAN_ETH_HLEN))
>> > + skb->mac_len < VLAN_ETH_HLEN))
>>
>> There is already check in __skb_vlan_pop() to validate skb for a vlan
>> header. So it is safe to drop this check entirely.
>
> Yep, I submitted a v2 with your suggestion, however I withdrew it, as
> there is a slight behavior difference noticable by 'skb_vlan_pop' callers.
>
> Suppose the rare case where skb->len is too small.
>
> pre:
> skb_vlan_pop returns 0 (at least for the correct tx path).
> Meaning, callers do not see it as a failure.
> post:
> skb_ensure_writable fails (!pskb_may_pull), therefore -ENOMEM returned
> to the callers of 'skb_vlan_pop'.
>
> For ovs, it means do_execute_actions's loop is terminated, no further
> actions are executed, and skb gets freed.
>
> For tc act vlan, it means skb gets dropped.
>
> This actually makes sense, but do we want to present this change?
>
I think this is correct behavior over existing code. And under memory
pressure chances of packet drop are higher even without the change
anyways.
