ip_gre: set tunnel hlen properly in erspan_tunnel_init

According to __gre_tunnel_init, tunnel->hlen should be set as the
headers' length between inner packet and outer iphdr.

It would be used especially to calculate a proper mtu when updating
mtu in tnl_update_pmtu. Now without setting it, a bigger mtu value
than expected would be updated, which hurts performance a lot.

This patch is to fix it by setting tunnel->hlen with:
   tunnel->tun_hlen + tunnel->encap_hlen + sizeof(struct erspanhdr)

Fixes: 84e54fe0a5ea ("gre: introduce native tunnel support for ERSPAN")
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 1 deletions

diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index 2a4ef9dc48ff..fad0bb1e3e9a 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -1245,7 +1245,9 @@ static int erspan_tunnel_init(struct net_device *dev)
 
         tunnel->tun_hlen = 8;
         tunnel->parms.iph.protocol = IPPROTO_GRE;
-        t_hlen = tunnel->hlen + sizeof(struct iphdr) + sizeof(struct erspanhdr);
+        tunnel->hlen = tunnel->tun_hlen + tunnel->encap_hlen +
+                       sizeof(struct erspanhdr);
+        t_hlen = tunnel->hlen + sizeof(struct iphdr);
 
         dev->needed_headroom = LL_MAX_HEADER + t_hlen + 4;
         dev->mtu = ETH_DATA_LEN - t_hlen - 4;