[PATCH v3 2/2] macvtap: Allow tap features change when IFF_VNET_HDR is disabled.

[Vlad Yasevich <vyasevic@redhat.com>]

When the user turns off IFF_VNET_HDR flag, attempts to change
offload features via TUNSETOFFLOAD do not work.  This could cause
GSO packets to be delivered to the user when the user is
not prepared to handle them.

To solve, allow processing of TUNSETOFFLOAD when IFF_VNET_HDR is
disabled.  Also, take the setting of IFF_VNET_HDR into consideration
when determining the feature set to apply to incommig traffic.
If IFF_VNET_HDR is set, we use user-specfied feature set.  if the
IFF_VNET_HDR is clear, we mask off all tun-specific offload features,
since user can not be notified of the possbile offloads.

Signed-off-by: Vlad Yasevich <vyasevic@redhat.com>
---
 drivers/net/macvtap.c | 30 ++++++++++++++++++++++++------
 1 file changed, 24 insertions(+), 6 deletions(-)

diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
index 8121358..df45a59 100644
--- a/drivers/net/macvtap.c
+++ b/drivers/net/macvtap.c
@@ -269,6 +269,28 @@ static void macvtap_del_queues(struct net_device *dev)
 		sock_put(&qlist[j]->sk);
 }
 
+/* Determine features to be applied to the packet as it
+ * gets sent to the tap.  The features depend on the offloads
+ * set by user and by whether or not IFF_VNET_HDR is enabled.
+ */
+static netdev_features_t macvtap_skb_features(struct sk_buff *skb,
+					      struct macvtap_queue *q)
+{
+	struct macvlan_dev *vlan = netdev_priv(skb->dev);
+	netdev_features_t features = netif_skb_features(skb);
+
+	/* If VNET_HDR is enabled, user can receive offload info so
+	 * use user-specified tap_features.
+	 * Otherwise, mask off all tap offload features.
+	 */
+	if (q->flags & IFF_VNET_HDR)
+		features &= vlan->tap_features;
+	else
+		features &= ~TUN_OFFLOADS;
+
+	return features;
+}
+
 /*
  * Forward happens for data that gets sent from one macvlan
  * endpoint to another one in bridge mode. We just take
@@ -276,9 +298,9 @@ static void macvtap_del_queues(struct net_device *dev)
  */
 static int macvtap_forward(struct net_device *dev, struct sk_buff *skb)
 {
-	struct macvlan_dev *vlan = netdev_priv(dev);
 	struct macvtap_queue *q = macvtap_get_queue(dev, skb);
 	netdev_features_t features;
+
 	if (!q)
 		goto drop;
 
@@ -289,7 +311,7 @@ static int macvtap_forward(struct net_device *dev, struct sk_buff *skb)
 	/* Apply the forward feature mask so that we perform segmentation
 	 * according to users wishes.
 	 */
-	features = netif_skb_features(skb) & vlan->tap_features;
+	features = macvtap_skb_features(skb, q);
 	if (netif_needs_gso(skb, features)) {
 		struct sk_buff *segs = __skb_gso_segment(skb, features, false);
 
@@ -1161,10 +1183,6 @@ static long macvtap_ioctl(struct file *file, unsigned int cmd,
 			    TUN_F_TSO_ECN | TUN_F_UFO))
 			return -EINVAL;
 
-		/* TODO: only accept frames with the features that
-			 got enabled for forwarded frames */
-		if (!(q->flags & IFF_VNET_HDR))
-			return  -EINVAL;
 		rtnl_lock();
 		ret = set_offload(q, arg);
 		rtnl_unlock();
-- 
1.8.1.4