net: skbuff: Remove errornous length validation in skb_vlan_pop()

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 skb has non hw-accel vlan tag, the original 'pop_vlan()' assured
that skb->len is sufficient (if skb->len < VLAN_ETH_HLEN then pop was
considered a no-op).

This validation was moved as is into the new common 'skb_vlan_pop'.

Alas, in its original location (openvswitch), there was 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 the non
hw-accel case) or to fail moving next tag into hw-accel tag.

Remove the 'skb->len < VLAN_ETH_HLEN' condition entirely:
It is superfluous since inner '__skb_vlan_pop' already verifies there
are VLAN_ETH_HLEN writable bytes at the mac_header.

Note this presents a slight change to skb_vlan_pop() users:
In case total length is smaller than VLAN_ETH_HLEN, skb_vlan_pop() now
returns an error, as opposed to previous "no-op" behavior.
Existing callers (e.g. tc act vlan, ovs) usually drop the packet if
'skb_vlan_pop' fails.

Fixes: 93515d53b1 ("net: move vlan pop/push functions into common code")
Signed-off-by: Shmulik Ladkani <shmulik.ladkani@gmail.com>
Cc: Pravin Shelar <pshelar@ovn.org>
Reviewed-by: Pravin B Shelar <pshelar@ovn.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 6c22351..b2a51bf 100644 (file)
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -4567,9 +4567,8 @@ int skb_vlan_pop(struct sk_buff *skb)
        if (likely(skb_vlan_tag_present(skb))) {
                skb->vlan_tci = 0;
        } else {
-               if (unlikely((skb->protocol != htons(ETH_P_8021Q) &&
-                             skb->protocol != htons(ETH_P_8021AD)) ||
-                            skb->len < VLAN_ETH_HLEN))
+               if (unlikely(skb->protocol != htons(ETH_P_8021Q) &&
+                            skb->protocol != htons(ETH_P_8021AD)))
                        return 0;
 
                err = __skb_vlan_pop(skb, &vlan_tci);
@@ -4577,9 +4576,8 @@ int skb_vlan_pop(struct sk_buff *skb)
                        return err;
        }
        /* move next vlan tag to hw accel tag */
-       if (likely((skb->protocol != htons(ETH_P_8021Q) &&
-                   skb->protocol != htons(ETH_P_8021AD)) ||
-                  skb->len < VLAN_ETH_HLEN))
+       if (likely(skb->protocol != htons(ETH_P_8021Q) &&
+                  skb->protocol != htons(ETH_P_8021AD)))
                return 0;
 
        vlan_proto = skb->protocol;