[PATCH net] vxlan: calculate correct header length for GPE

[Jiri Benc <jbenc@redhat.com>]

VXLAN-GPE does not add an extra inner Ethernet header. Take that into
account when calculating header length.

This causes problems in skb_tunnel_check_pmtu, where incorrect PMTU is
cached. If the VXLAN-GPE interface has MTU 1464 set (with the underlying
interface having the usual MTU of 1500), a TCP stream sent over the
tunnel is first segmented to 1514 byte frames only to be immediatelly
followed by a resend with 1500 bytes frames, before the other side even
has a chance to ack them.

Fixes: e1e5314de08ba ("vxlan: implement GPE")
Signed-off-by: Jiri Benc <jbenc@redhat.com>
---
 drivers/net/ethernet/intel/ixgbe/ixgbe_main.c |  2 +-
 drivers/net/vxlan/vxlan_core.c                | 23 ++++++++-----------
 include/net/vxlan.h                           | 13 +++++++----
 3 files changed, 20 insertions(+), 18 deletions(-)

diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
index 1726297f2e0d..8eb9839a3ca6 100644
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
@@ -8479,7 +8479,7 @@ static void ixgbe_atr(struct ixgbe_ring *ring,
 		struct ixgbe_adapter *adapter = q_vector->adapter;
 
 		if (unlikely(skb_tail_pointer(skb) < hdr.network +
-			     VXLAN_HEADROOM))
+			     vxlan_headroom(0)))
 			return;
 
 		/* verify the port is recognized as VXLAN */
diff --git a/drivers/net/vxlan/vxlan_core.c b/drivers/net/vxlan/vxlan_core.c
index 78744549c1b3..42be8a26c171 100644
--- a/drivers/net/vxlan/vxlan_core.c
+++ b/drivers/net/vxlan/vxlan_core.c
@@ -2516,7 +2516,7 @@ void vxlan_xmit_one(struct sk_buff *skb, struct net_device *dev,
 		}
 
 		ndst = &rt->dst;
-		err = skb_tunnel_check_pmtu(skb, ndst, VXLAN_HEADROOM,
+		err = skb_tunnel_check_pmtu(skb, ndst, vxlan_headroom(flags & VXLAN_F_GPE),
 					    netif_is_any_bridge_port(dev));
 		if (err < 0) {
 			goto tx_error;
@@ -2577,7 +2577,8 @@ void vxlan_xmit_one(struct sk_buff *skb, struct net_device *dev,
 				goto out_unlock;
 		}
 
-		err = skb_tunnel_check_pmtu(skb, ndst, VXLAN6_HEADROOM,
+		err = skb_tunnel_check_pmtu(skb, ndst,
+					    vxlan_headroom((flags & VXLAN_F_GPE) | VXLAN_F_IPV6),
 					    netif_is_any_bridge_port(dev));
 		if (err < 0) {
 			goto tx_error;
@@ -2989,14 +2990,12 @@ static int vxlan_change_mtu(struct net_device *dev, int new_mtu)
 	struct vxlan_rdst *dst = &vxlan->default_dst;
 	struct net_device *lowerdev = __dev_get_by_index(vxlan->net,
 							 dst->remote_ifindex);
-	bool use_ipv6 = !!(vxlan->cfg.flags & VXLAN_F_IPV6);
 
 	/* This check is different than dev->max_mtu, because it looks at
 	 * the lowerdev->mtu, rather than the static dev->max_mtu
 	 */
 	if (lowerdev) {
-		int max_mtu = lowerdev->mtu -
-			      (use_ipv6 ? VXLAN6_HEADROOM : VXLAN_HEADROOM);
+		int max_mtu = lowerdev->mtu - vxlan_headroom(vxlan->cfg.flags);
 		if (new_mtu > max_mtu)
 			return -EINVAL;
 	}
@@ -3644,11 +3643,11 @@ static void vxlan_config_apply(struct net_device *dev,
 	struct vxlan_dev *vxlan = netdev_priv(dev);
 	struct vxlan_rdst *dst = &vxlan->default_dst;
 	unsigned short needed_headroom = ETH_HLEN;
-	bool use_ipv6 = !!(conf->flags & VXLAN_F_IPV6);
 	int max_mtu = ETH_MAX_MTU;
+	u32 flags = conf->flags;
 
 	if (!changelink) {
-		if (conf->flags & VXLAN_F_GPE)
+		if (flags & VXLAN_F_GPE)
 			vxlan_raw_setup(dev);
 		else
 			vxlan_ether_setup(dev);
@@ -3673,8 +3672,7 @@ static void vxlan_config_apply(struct net_device *dev,
 
 		dev->needed_tailroom = lowerdev->needed_tailroom;
 
-		max_mtu = lowerdev->mtu - (use_ipv6 ? VXLAN6_HEADROOM :
-					   VXLAN_HEADROOM);
+		max_mtu = lowerdev->mtu - vxlan_headroom(flags);
 		if (max_mtu < ETH_MIN_MTU)
 			max_mtu = ETH_MIN_MTU;
 
@@ -3685,10 +3683,9 @@ static void vxlan_config_apply(struct net_device *dev,
 	if (dev->mtu > max_mtu)
 		dev->mtu = max_mtu;
 
-	if (use_ipv6 || conf->flags & VXLAN_F_COLLECT_METADATA)
-		needed_headroom += VXLAN6_HEADROOM;
-	else
-		needed_headroom += VXLAN_HEADROOM;
+	if (flags & VXLAN_F_COLLECT_METADATA)
+		flags |= VXLAN_F_IPV6;
+	needed_headroom += vxlan_headroom(flags);
 	dev->needed_headroom = needed_headroom;
 
 	memcpy(&vxlan->cfg, conf, sizeof(*conf));
diff --git a/include/net/vxlan.h b/include/net/vxlan.h
index 0be91ca78d3a..1648240c9668 100644
--- a/include/net/vxlan.h
+++ b/include/net/vxlan.h
@@ -386,10 +386,15 @@ static inline netdev_features_t vxlan_features_check(struct sk_buff *skb,
 	return features;
 }
 
-/* IP header + UDP + VXLAN + Ethernet header */
-#define VXLAN_HEADROOM (20 + 8 + 8 + 14)
-/* IPv6 header + UDP + VXLAN + Ethernet header */
-#define VXLAN6_HEADROOM (40 + 8 + 8 + 14)
+static inline int vxlan_headroom(u32 flags)
+{
+	/* VXLAN:     IP4/6 header + UDP + VXLAN + Ethernet header */
+	/* VXLAN-GPE: IP4/6 header + UDP + VXLAN */
+	return (flags & VXLAN_F_IPV6 ? sizeof(struct ipv6hdr) :
+				       sizeof(struct iphdr)) +
+	       sizeof(struct udphdr) + sizeof(struct vxlanhdr) +
+	       (flags & VXLAN_F_GPE ? 0 : ETH_HLEN);
+}
 
 static inline struct vxlanhdr *vxlan_hdr(struct sk_buff *skb)
 {
-- 
2.39.2