vlan: Fix tcp checksum offloads in Q-in-Q vlans

It appears that TCP checksum offloading has been broken for
Q-in-Q vlans.  The behavior was execerbated by the
series
    commit e5a343097db6 ("Merge branch 'stacked_vlan_tso'")
that that enabled accleleration features on stacked vlans.

However, event without that series, it is possible to trigger
this issue.  It just requires a lot more specialized configuration.

The root cause is the interaction between how
netdev_intersect_features() works, the features actually set on
the vlan devices and HW having the ability to run checksum with
longer headers.

The issue starts when netdev_interesect_features() replaces
NETIF_F_HW_CSUM with a combination of NETIF_F_IP_CSUM | NETIF_F_IPV6_CSUM,
if the HW advertises IP|IPV6 specific checksums.  This happens
for tagged and multi-tagged packets.   However, HW that enables
IP|IPV6 checksum offloading doesn't gurantee that packets with
arbitrarily long headers can be checksummed.

This patch disables IP|IPV6 checksums on the packet for multi-tagged
packets.

CC: Toshiaki Makita <makita.toshiaki@lab.ntt.co.jp>
CC: Michal Kubecek <mkubecek@suse.cz>
Signed-off-by: Vladislav Yasevich <vyasevic@redhat.com>
Acked-by: Toshiaki Makita <makita.toshiaki@lab.ntt.co.jp>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/linux/if_vlan.h b/include/linux/if_vlan.h
index 8d5fcd6284ce0f4702d9eb28703bf2ae80d7e399..283dc2f5364d77c13df5a16ed0474154ee6724ff 100644 (file)
--- a/include/linux/if_vlan.h
+++ b/include/linux/if_vlan.h
@@ -614,14 +614,16 @@ static inline bool skb_vlan_tagged_multi(const struct sk_buff *skb)
 static inline netdev_features_t vlan_features_check(const struct sk_buff *skb,
                                                    netdev_features_t features)
 {
-       if (skb_vlan_tagged_multi(skb))
-               features = netdev_intersect_features(features,
-                                                    NETIF_F_SG |
-                                                    NETIF_F_HIGHDMA |
-                                                    NETIF_F_FRAGLIST |
-                                                    NETIF_F_HW_CSUM |
-                                                    NETIF_F_HW_VLAN_CTAG_TX |
-                                                    NETIF_F_HW_VLAN_STAG_TX);
+       if (skb_vlan_tagged_multi(skb)) {
+               /* In the case of multi-tagged packets, use a direct mask
+                * instead of using netdev_interesect_features(), to make
+                * sure that only devices supporting NETIF_F_HW_CSUM will
+                * have checksum offloading support.
+                */
+               features &= NETIF_F_SG | NETIF_F_HIGHDMA | NETIF_F_HW_CSUM |
+                           NETIF_F_FRAGLIST | NETIF_F_HW_VLAN_CTAG_TX |
+                           NETIF_F_HW_VLAN_STAG_TX;
+       }
 
        return features;
 }