On Mon, 19 Sep 2016 14:22:57 +0200, dan...@iogearbox.net wrote: > On 09/19/2016 08:15 AM, Shmulik Ladkani wrote: > > On Sun, 18 Sep 2016 13:26:30 -0700, pshe...@ovn.org wrote: > >> On Sun, Sep 18, 2016 at 3:09 AM, Shmulik Ladkani > >> <shmulik.ladk...@gmail.com> wrote: > >>> diff --git a/net/core/skbuff.c b/net/core/skbuff.c > >>> index 1e329d4112..cc2c004838 100644 > >>> --- a/net/core/skbuff.c > >>> +++ 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. > > > > Seems validation in '__skb_vlan_pop' has slightly different semantics: > > > > unsigned int offset = skb->data - skb_mac_header(skb); > > > > __skb_push(skb, offset); > > err = skb_ensure_writable(skb, VLAN_ETH_HLEN); > > > > this pushes 'data' back to mac_header, then makes sure there's sufficient > > place in skb to _store_ VLAN_ETH_HLEN bytes (by pulling into linear part > > if needed, or erroring if skb is too small). > > Yes, but this skb_ensure_writable() is needed for doing the memmove anyway.
Had no intention dropping the skb_ensure_writable from __skb_vlan_pop :) > > There's no guarantee the original mac header was sized VLAN_ETH_HLEN. > > I'm wondering, what happens when you'd call this on tx path, when you'd > change that to suggested skb->mac_len? Isn't that 0 in such case, thus > such setups could fail then? Thanks, I think you're right. Seems __dev_queue_xmit needs a 'skb_reset_mac_len' right after call to 'skb_reset_mac_header' (or maybe call 'skb_reset_mac_len' from within skb_reset_mac_header?). Also, I'm okay with removing the excess 'skb->mac_len < VLAN_ETH_HLEN' condition if it is agreed that the "tag exists but insufficient to pop" semantic is no longer wanted. Regards, Shmulik