[NET]: Avoid allocating skb in skb_pad

First of all it is unnecessary to allocate a new skb in skb_pad since
the existing one is not shared.  More importantly, our hard_start_xmit
interface does not allow a new skb to be allocated since that breaks
requeueing.

This patch uses pskb_expand_head to expand the existing skb and linearize
it if needed.  Actually, someone should sift through every instance of
skb_pad on a non-linear skb as they do not fit the reasons why this was
originally created.

Incidentally, this fixes a minor bug when the skb is cloned (tcpdump,
TCP, etc.).  As it is skb_pad will simply write over a cloned skb.  Because
of the position of the write it is unlikely to cause problems but still
it's best if we don't do it.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 1 insertions, 2 deletions

diff --git a/drivers/net/znet.c b/drivers/net/znet.c
index 3ac047bc727d..a7c089df66e6 100644
--- a/drivers/net/znet.c
+++ b/drivers/net/znet.c
@@ -544,8 +544,7 @@ static int znet_send_packet(struct sk_buff *skb, struct net_device *dev)
                 printk(KERN_DEBUG "%s: ZNet_send_packet.\n", dev->name);
 
         if (length < ETH_ZLEN) {
-                skb = skb_padto(skb, ETH_ZLEN);
-                if (skb == NULL)
+                if (skb_padto(skb, ETH_ZLEN))
                         return 0;
                 length = ETH_ZLEN;
         }