[SK_BUFF]: Fix missing offset adjustment in skb_copy_expand

skb_copy_expand changes the headroom, so it needs to adjust the header
offsets by the difference between the old and the new value.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/skbuff.c

@@ -736,7 +736,9 @@ struct sk_buff *skb_copy_expand(const struct sk_buff *skb,
 	 */
 	struct sk_buff *n = alloc_skb(newheadroom + skb->len + newtailroom,
 				      gfp_mask);
+	int oldheadroom = skb_headroom(skb);
 	int head_copy_len, head_copy_off;
+	int off = 0;
 
 	if (!n)
 		return NULL;
@@ -746,7 +748,7 @@ struct sk_buff *skb_copy_expand(const struct sk_buff *skb,
 	/* Set the tail pointer and length */
 	skb_put(n, skb->len);
 
-	head_copy_len = skb_headroom(skb);
+	head_copy_len = oldheadroom;
 	head_copy_off = 0;
 	if (newheadroom <= head_copy_len)
 		head_copy_len = newheadroom;
@@ -760,6 +762,13 @@ struct sk_buff *skb_copy_expand(const struct sk_buff *skb,
 
 	copy_skb_header(n, skb);
 
+#ifdef NET_SKBUFF_DATA_USES_OFFSET
+	off                  = newheadroom - oldheadroom;
+#endif
+	n->transport_header += off;
+	n->network_header   += off;
+	n->mac_header	    += off;
+
 	return n;
 }