On Sun, Sep 18, 2016 at 3:09 AM, Shmulik Ladkani <shmulik.ladk...@gmail.com> wrote: > In 93515d53b1 > "net: move vlan pop/push functions into common code" > skb_vlan_pop was moved from its private location in openvswitch to > skbuff common code. > > In case !vlan_tx_tag_present, the original 'pop_vlan()' assured > that skb->len is sufficient for the existence of a vlan_ethhdr > (if skb->len < VLAN_ETH_HLEN then pop was a no-op). > > This validation was moved as is into the new common 'skb_vlan_pop'. > > Alas, in its original location (openvswitch), there's a guarantee that > 'data' points to the mac_header, therefore the 'skb->len < VLAN_ETH_HLEN' > condition made sense. > However there's no such guarantee in the generic 'skb_vlan_pop'. > > For short packets received in rx path going through 'skb_vlan_pop', > this causes 'skb_vlan_pop' to fail pop-ing a valid vlan hdr (in case tag > is in payload), or to fail moving next tag into hw-accel tag. > > Instead, verify that 'skb->mac_len' is sufficient. > > Signed-off-by: Shmulik Ladkani <shmulik.ladk...@gmail.com> > --- > Spotted by code review while doing work augmenting tc act vlan. > > net/core/skbuff.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > 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.