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.

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?

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