vlan: avoid header copying and linearisation where possible

- vlan_dev_reorder_header() is only called on the receive path after
  calling skb_share_check(). This means we can use skb_cow() since
  all we need is a writable header.

- vlan_dev_hard_header() includes a work-around for some apparently
  broken out of tree MPLS code. The hard_header functions can expect
  to always have a headroom of at least there own hard_header_len
  available, so the reallocation check is unnecessary.

- __vlan_put_tag() can use skb_cow_head() to avoid the skb_unshare()
  copy when the header is writable.

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

1 files changed, 5 insertions, 29 deletions

diff --git a/net/8021q/vlan_dev.c b/net/8021q/vlan_dev.c
index 2ccac6bea57e..b6e52c025fd8 100644
--- a/net/8021q/vlan_dev.c
+++ b/net/8021q/vlan_dev.c
@@ -74,11 +74,8 @@ static int vlan_dev_rebuild_header(struct sk_buff *skb)
 static inline struct sk_buff *vlan_check_reorder_header(struct sk_buff *skb)
 {
         if (vlan_dev_info(skb->dev)->flags & VLAN_FLAG_REORDER_HDR) {
-                if (skb_shared(skb) || skb_cloned(skb)) {
-                        struct sk_buff *nskb = skb_copy(skb, GFP_ATOMIC);
-                        kfree_skb(skb);
-                        skb = nskb;
-                }
+                if (skb_cow(skb, skb_headroom(skb)) < 0)
+                        skb = NULL;
                 if (skb) {
                         /* Lifted from Gleb's VLAN code... */
                         memmove(skb->data - ETH_HLEN,
@@ -262,12 +259,14 @@ static int vlan_dev_hard_header(struct sk_buff *skb, struct net_device *dev,
         u16 vlan_tci = 0;
         int rc = 0;
         int build_vlan_header = 0;
-        struct net_device *vdev = dev;
 
         pr_debug("%s: skb: %p type: %hx len: %u vlan_id: %hx, daddr: %p\n",
                  __func__, skb, type, len, vlan_dev_info(dev)->vlan_id,
                  daddr);
 
+        if (WARN_ON(skb_headroom(skb) < dev->hard_header_len))
+                return -ENOSPC;
+
         /* build vlan header only if re_order_header flag is NOT set.  This
          * fixes some programs that get confused when they see a VLAN device
          * sending a frame that is VLAN encoded (the consensus is that the VLAN
@@ -316,29 +315,6 @@ static int vlan_dev_hard_header(struct sk_buff *skb, struct net_device *dev,
 
         dev = vlan_dev_info(dev)->real_dev;
 
-        /* MPLS can send us skbuffs w/out enough space. This check will grow
-         * the skb if it doesn't have enough headroom. Not a beautiful solution,
-         * so I'll tick a counter so that users can know it's happening...
-         * If they care...
-         */
-
-        /* NOTE: This may still break if the underlying device is not the final
-         * device (and thus there are more headers to add...) It should work for
-         * good-ole-ethernet though.
-         */
-        if (skb_headroom(skb) < dev->hard_header_len) {
-                struct sk_buff *sk_tmp = skb;
-                skb = skb_realloc_headroom(sk_tmp, dev->hard_header_len);
-                kfree_skb(sk_tmp);
-                if (skb == NULL) {
-                        struct net_device_stats *stats = &vdev->stats;
-                        stats->tx_dropped++;
-                        return -ENOMEM;
-                }
-                vlan_dev_info(vdev)->cnt_inc_headroom_on_tx++;
-                pr_debug("%s: %s: had to grow skb\n", __func__, vdev->name);
-        }
-
         if (build_vlan_header) {
                 /* Now make the underlying real hard header */
                 rc = dev_hard_header(skb, dev, ETH_P_8021Q, daddr, saddr,