[PPP] generic: Call skb_cow_head before scribbling over skb

It's rude to write over data that other people are still using.  So call
skb_cow_head before PPP proceeds to modify the skb data.

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

1 files changed, 3 insertions, 11 deletions

diff --git a/drivers/net/ppp_generic.c b/drivers/net/ppp_generic.c
index 9293c82ef2af..7e21342becb2 100644
--- a/drivers/net/ppp_generic.c
+++ b/drivers/net/ppp_generic.c
@@ -899,17 +899,9 @@ ppp_start_xmit(struct sk_buff *skb, struct net_device *dev)
 
         /* Put the 2-byte PPP protocol number on the front,
            making sure there is room for the address and control fields. */
-        if (skb_headroom(skb) < PPP_HDRLEN) {
-                struct sk_buff *ns;
-
-                ns = alloc_skb(skb->len + dev->hard_header_len, GFP_ATOMIC);
-                if (ns == 0)
-                        goto outf;
-                skb_reserve(ns, dev->hard_header_len);
-                skb_copy_bits(skb, 0, skb_put(ns, skb->len), skb->len);
-                kfree_skb(skb);
-                skb = ns;
-        }
+        if (skb_cow_head(skb, PPP_HDRLEN))
+                goto outf;
+
         pp = skb_push(skb, 2);
         proto = npindex_to_proto[npi];
         pp[0] = proto >> 8;