net: Fix some corner cases in dev_can_checksum()

dev_can_checksum() incorrectly returns true in these cases:

1. The skb has both out-of-band and in-band VLAN tags and the device
   supports checksum offload for the encapsulated protocol but only with
   one layer of encapsulation.
2. The skb has a VLAN tag and the device supports generic checksumming
   but not in conjunction with VLAN encapsulation.

Rearrange the VLAN tag checks to avoid these.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/dev.c b/net/core/dev.c
index e8a8dc19365b18a3b77ac5eacdaa1ba9568f8aaf..3c5fbfbb318146edb0f7591acbb48be879a384c0 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1696,22 +1696,18 @@ static bool can_checksum_protocol(unsigned long features, __be16 protocol)
 
 static bool dev_can_checksum(struct net_device *dev, struct sk_buff *skb)
 {
+       __be16 protocol = skb->protocol;
        int features = dev->features;
 
-       if (vlan_tx_tag_present(skb))
+       if (vlan_tx_tag_present(skb)) {
                features &= dev->vlan_features;
-
-       if (can_checksum_protocol(features, skb->protocol))
-               return true;
-
-       if (skb->protocol == htons(ETH_P_8021Q)) {
+       } else if (protocol == htons(ETH_P_8021Q)) {
                struct vlan_ethhdr *veh = (struct vlan_ethhdr *)skb->data;
-               if (can_checksum_protocol(dev->features & dev->vlan_features,
-                                         veh->h_vlan_encapsulated_proto))
-                       return true;
+               protocol = veh->h_vlan_encapsulated_proto;
+               features &= dev->vlan_features;
        }
 
-       return false;
+       return can_checksum_protocol(features, protocol);
 }
 
 /**