3 files changed, 33 insertions, 11 deletions

diff --git a/drivers/net/pppoe.c b/drivers/net/pppoe.c
index bac36546e0bf..0d7f570b9a54 100644
--- a/drivers/net/pppoe.c
+++ b/drivers/net/pppoe.c
@@ -860,7 +860,7 @@ static int __pppoe_xmit(struct sock *sk, struct sk_buff *skb)
         /* Copy the data if there is no space for the header or if it's
          * read-only.
          */
-        if (skb_cow(skb, sizeof(*ph) + dev->hard_header_len))
+        if (skb_cow_head(skb, sizeof(*ph) + dev->hard_header_len))
                 goto abort;
 
         __skb_push(skb, sizeof(*ph));
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 93c27f71122a..a656cecd373c 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -1352,6 +1352,22 @@ static inline int skb_clone_writable(struct sk_buff *skb, int len)
                skb_headroom(skb) + len <= skb->hdr_len;
 }
 
+static inline int __skb_cow(struct sk_buff *skb, unsigned int headroom,
+                            int cloned)
+{
+        int delta = 0;
+
+        if (headroom < NET_SKB_PAD)
+                headroom = NET_SKB_PAD;
+        if (headroom > skb_headroom(skb))
+                delta = headroom - skb_headroom(skb);
+
+        if (delta || cloned)
+                return pskb_expand_head(skb, ALIGN(delta, NET_SKB_PAD), 0,
+                                        GFP_ATOMIC);
+        return 0;
+}
+
 /**
  *      skb_cow - copy header of skb when it is required
  *      @skb: buffer to cow
@@ -1366,16 +1382,22 @@ static inline int skb_clone_writable(struct sk_buff *skb, int len)
  */
 static inline int skb_cow(struct sk_buff *skb, unsigned int headroom)
 {
-        int delta = (headroom > NET_SKB_PAD ? headroom : NET_SKB_PAD) -
-                        skb_headroom(skb);
-
-        if (delta < 0)
-                delta = 0;
+        return __skb_cow(skb, headroom, skb_cloned(skb));
+}
 
-        if (delta || skb_cloned(skb))
-                return pskb_expand_head(skb, (delta + (NET_SKB_PAD-1)) &
-                                ~(NET_SKB_PAD-1), 0, GFP_ATOMIC);
-        return 0;
+/**
+ *      skb_cow_head - skb_cow but only making the head writable
+ *      @skb: buffer to cow
+ *      @headroom: needed headroom
+ *
+ *      This function is identical to skb_cow except that we replace the
+ *      skb_cloned check by skb_header_cloned.  It should be used when
+ *      you only need to push on some header and do not need to modify
+ *      the data.
+ */
+static inline int skb_cow_head(struct sk_buff *skb, unsigned int headroom)
+{
+        return __skb_cow(skb, headroom, skb_header_cloned(skb));
 }
 
 /**
diff --git a/net/bridge/br_netfilter.c b/net/bridge/br_netfilter.c
index 3ee2022928e3..fc13130035e7 100644
--- a/net/bridge/br_netfilter.c
+++ b/net/bridge/br_netfilter.c
@@ -183,7 +183,7 @@ int nf_bridge_copy_header(struct sk_buff *skb)
         int err;
         int header_size = ETH_HLEN + nf_bridge_encap_header_len(skb);
 
-        err = skb_cow(skb, header_size);
+        err = skb_cow_head(skb, header_size);
         if (err)
                 return err;