vlan: Fix header ops passthru when doing TX VLAN offload.

When the vlan code detects that the real device can do TX VLAN offloads
in hardware, it tries to arrange for the real device's header_ops to
be invoked directly.

But it does so illegally, by simply hooking the real device's
header_ops up to the VLAN device.

This doesn't work because we will end up invoking a set of header_ops
routines which expect a device type which matches the real device, but
will see a VLAN device instead.

Fix this by providing a pass-thru set of header_ops which will arrange
to pass the proper real device instead.

To facilitate this add a dev_rebuild_header().  There are
implementations which provide a ->cache and ->create but not a
->rebuild (f.e. PLIP).  So we need a helper function just like
dev_hard_header() to avoid crashes.

Use this helper in the one existing place where the
header_ops->rebuild was being invoked, the neighbour code.

With lots of help from Florian Westphal.

Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 19 insertions, 2 deletions

diff --git a/net/8021q/vlan_dev.c b/net/8021q/vlan_dev.c
index 762896ebfcf5..47c908f1f626 100644
--- a/net/8021q/vlan_dev.c
+++ b/net/8021q/vlan_dev.c
@@ -530,6 +530,23 @@ static const struct header_ops vlan_header_ops = {
 	.parse	 = eth_header_parse,
 };
 
+static int vlan_passthru_hard_header(struct sk_buff *skb, struct net_device *dev,
+				     unsigned short type,
+				     const void *daddr, const void *saddr,
+				     unsigned int len)
+{
+	struct vlan_dev_priv *vlan = vlan_dev_priv(dev);
+	struct net_device *real_dev = vlan->real_dev;
+
+	return dev_hard_header(skb, real_dev, type, daddr, saddr, len);
+}
+
+static const struct header_ops vlan_passthru_header_ops = {
+	.create	 = vlan_passthru_hard_header,
+	.rebuild = dev_rebuild_header,
+	.parse	 = eth_header_parse,
+};
+
 static struct device_type vlan_type = {
 	.name	= "vlan",
 };
@@ -573,7 +590,7 @@ static int vlan_dev_init(struct net_device *dev)
 
 	dev->needed_headroom = real_dev->needed_headroom;
 	if (real_dev->features & NETIF_F_HW_VLAN_CTAG_TX) {
-		dev->header_ops      = real_dev->header_ops;
+		dev->header_ops      = &vlan_passthru_header_ops;
 		dev->hard_header_len = real_dev->hard_header_len;
 	} else {
 		dev->header_ops      = &vlan_header_ops;
diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 36b1443f9ae4..932c6d7cf666 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -1275,7 +1275,7 @@ int neigh_compat_output(struct neighbour *neigh, struct sk_buff *skb)
 
 	if (dev_hard_header(skb, dev, ntohs(skb->protocol), NULL, NULL,
 			    skb->len) < 0 &&
-	    dev->header_ops->rebuild(skb))
+	    dev_rebuild_header(skb))
 		return 0;
 
 	return dev_queue_xmit(skb);