6lowpan: Use skb_cow in IPHC decompression.

Currently there are potentially 2 skb_copy_expand calls in IPHC
decompression.  This patch replaces this with one call to
skb_cow which will check to see if there is enough headroom
first to ensure it's only done if necessary and will handle
alignment issues for cache.
As skb_cow uses pskb_expand_head we ensure the skb isn't shared from
bluetooth and ieee802.15.4 code that use the IPHC decompression.

Signed-off-by: Martin Townsend <martin.townsend@xsilon.com>
Acked-by: Alexander Aring <alex.aring@gmail.com>
Acked-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

1 files changed, 21 insertions, 26 deletions

diff --git a/net/6lowpan/iphc.c b/net/6lowpan/iphc.c
index 142eef55c9e2..747b3ccfc4f8 100644
--- a/net/6lowpan/iphc.c
+++ b/net/6lowpan/iphc.c
@@ -174,30 +174,22 @@ static int uncompress_context_based_src_addr(struct sk_buff *skb,
 static int skb_deliver(struct sk_buff *skb, struct ipv6hdr *hdr,
                        struct net_device *dev, skb_delivery_cb deliver_skb)
 {
-        struct sk_buff *new;
         int stat;
 
-        new = skb_copy_expand(skb, sizeof(struct ipv6hdr), skb_tailroom(skb),
-                              GFP_ATOMIC);
-        kfree_skb(skb);
-
-        if (!new)
-                return -ENOMEM;
-
-        skb_push(new, sizeof(struct ipv6hdr));
-        skb_reset_network_header(new);
-        skb_copy_to_linear_data(new, hdr, sizeof(struct ipv6hdr));
+        skb_push(skb, sizeof(struct ipv6hdr));
+        skb_reset_network_header(skb);
+        skb_copy_to_linear_data(skb, hdr, sizeof(struct ipv6hdr));
 
-        new->protocol = htons(ETH_P_IPV6);
-        new->pkt_type = PACKET_HOST;
-        new->dev = dev;
+        skb->protocol = htons(ETH_P_IPV6);
+        skb->pkt_type = PACKET_HOST;
+        skb->dev = dev;
 
         raw_dump_table(__func__, "raw skb data dump before receiving",
-                       new->data, new->len);
+                       skb->data, skb->len);
 
-        stat = deliver_skb(new, dev);
+        stat = deliver_skb(skb, dev);
 
-        kfree_skb(new);
+        consume_skb(skb);
 
         return stat;
 }
@@ -460,7 +452,7 @@ int lowpan_process_data(struct sk_buff *skb, struct net_device *dev,
         /* UDP data uncompression */
         if (iphc0 & LOWPAN_IPHC_NH_C) {
                 struct udphdr uh;
-                struct sk_buff *new;
+                const int needed = sizeof(struct udphdr) + sizeof(hdr);
 
                 if (uncompress_udp_header(skb, &uh))
                         goto drop;
@@ -468,14 +460,11 @@ int lowpan_process_data(struct sk_buff *skb, struct net_device *dev,
                 /* replace the compressed UDP head by the uncompressed UDP
                  * header
                  */
-                new = skb_copy_expand(skb, sizeof(struct udphdr),
-                                      skb_tailroom(skb), GFP_ATOMIC);
-                kfree_skb(skb);
-
-                if (!new)
-                        return -ENOMEM;
-
-                skb = new;
+                err = skb_cow(skb, needed);
+                if (unlikely(err)) {
+                        kfree_skb(skb);
+                        return err;
+                }
 
                 skb_push(skb, sizeof(struct udphdr));
                 skb_reset_transport_header(skb);
@@ -485,6 +474,12 @@ int lowpan_process_data(struct sk_buff *skb, struct net_device *dev,
                                (u8 *)&uh, sizeof(uh));
 
                 hdr.nexthdr = UIP_PROTO_UDP;
+        } else {
+                err = skb_cow(skb, sizeof(hdr));
+                if (unlikely(err)) {
+                        kfree_skb(skb);
+                        return err;
+                }
         }
 
         hdr.payload_len = htons(skb->len);