geneve: Fix incorrect inner network header offset when innerprotoinherit is set

When innerprotoinherit is set, the tunneled packets do not have an inner
Ethernet header.
Change 'maclen' to not always assume the header length is ETH_HLEN, as
there might not be a MAC header.

This resolves issues with drivers (e.g. mlx5, in
mlx5e_tx_tunnel_accel()) who rely on the skb inner network header offset
to be correct, and use it for TX offloads.

Fixes: d8a6213d ("geneve: fix header validation in geneve[6]_xmit_skb")
Signed-off-by: Gal Pressman <gal@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Wojciech Drewek <wojciech.drewek@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/geneve.c

@@ -815,6 +815,7 @@ static int geneve_xmit_skb(struct sk_buff *skb, struct net_device *dev,
 			   struct geneve_dev *geneve,
 			   const struct ip_tunnel_info *info)
 {
+	bool inner_proto_inherit = geneve->cfg.inner_proto_inherit;
 	bool xnet = !net_eq(geneve->net, dev_net(geneve->dev));
 	struct geneve_sock *gs4 = rcu_dereference(geneve->sock4);
 	const struct ip_tunnel_key *key = &info->key;
@@ -826,7 +827,7 @@ static int geneve_xmit_skb(struct sk_buff *skb, struct net_device *dev,
 	__be16 sport;
 	int err;
 
-	if (!skb_vlan_inet_prepare(skb))
+	if (!skb_vlan_inet_prepare(skb, inner_proto_inherit))
 		return -EINVAL;
 
 	if (!gs4)
@@ -908,7 +909,7 @@ static int geneve_xmit_skb(struct sk_buff *skb, struct net_device *dev,
 	}
 
 	err = geneve_build_skb(&rt->dst, skb, info, xnet, sizeof(struct iphdr),
-			       geneve->cfg.inner_proto_inherit);
+			       inner_proto_inherit);
 	if (unlikely(err))
 		return err;
 
@@ -925,6 +926,7 @@ static int geneve6_xmit_skb(struct sk_buff *skb, struct net_device *dev,
 			    struct geneve_dev *geneve,
 			    const struct ip_tunnel_info *info)
 {
+	bool inner_proto_inherit = geneve->cfg.inner_proto_inherit;
 	bool xnet = !net_eq(geneve->net, dev_net(geneve->dev));
 	struct geneve_sock *gs6 = rcu_dereference(geneve->sock6);
 	const struct ip_tunnel_key *key = &info->key;
@@ -935,7 +937,7 @@ static int geneve6_xmit_skb(struct sk_buff *skb, struct net_device *dev,
 	__be16 sport;
 	int err;
 
-	if (!skb_vlan_inet_prepare(skb))
+	if (!skb_vlan_inet_prepare(skb, inner_proto_inherit))
 		return -EINVAL;
 
 	if (!gs6)
@@ -997,7 +999,7 @@ static int geneve6_xmit_skb(struct sk_buff *skb, struct net_device *dev,
 		ttl = ttl ? : ip6_dst_hoplimit(dst);
 	}
 	err = geneve_build_skb(dst, skb, info, xnet, sizeof(struct ipv6hdr),
-			       geneve->cfg.inner_proto_inherit);
+			       inner_proto_inherit);
 	if (unlikely(err))
 		return err;
 

include/net/ip_tunnels.h

@@ -461,9 +461,10 @@ static inline bool pskb_inet_may_pull(struct sk_buff *skb)
 
 /* Variant of pskb_inet_may_pull().
  */
-static inline bool skb_vlan_inet_prepare(struct sk_buff *skb)
+static inline bool skb_vlan_inet_prepare(struct sk_buff *skb,
+					 bool inner_proto_inherit)
 {
-	int nhlen = 0, maclen = ETH_HLEN;
+	int nhlen = 0, maclen = inner_proto_inherit ? 0 : ETH_HLEN;
 	__be16 type = skb->protocol;
 
 	/* Essentially this is skb_protocol(skb, true)