geneve: Refine MTU limit

Calculate the maximum MTU taking into account the size of headers
involved in GENEVE encapsulation, as for other tunnel types.

Changes in v3:
- Correct comment style
Changes in v2:
- Conform more closely to ip_tunnel_change_mtu
- Exclude GENEVE options from max MTU calculation

Signed-off-by: David Wragg <david@weave.works>
Acked-by: Jesse Gross <jesse@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/geneve.c b/drivers/net/geneve.c
index 028e3873c3107960c55f0bcff71d860fac0cad6e..70975700f91d493c847e618e79d6c3a17ef9bff9 100644 (file)
--- a/drivers/net/geneve.c
+++ b/drivers/net/geneve.c
@@ -1039,17 +1039,34 @@ static netdev_tx_t geneve_xmit(struct sk_buff *skb, struct net_device *dev)
        return geneve_xmit_skb(skb, dev, info);
 }
 
-static int geneve_change_mtu(struct net_device *dev, int new_mtu)
+static int __geneve_change_mtu(struct net_device *dev, int new_mtu, bool strict)
 {
-       /* GENEVE overhead is not fixed, so we can't enforce a more
-        * precise max MTU.
+       /* The max_mtu calculation does not take account of GENEVE
+        * options, to avoid excluding potentially valid
+        * configurations.
         */
-       if (new_mtu < 68 || new_mtu > IP_MAX_MTU)
+       int max_mtu = IP_MAX_MTU - GENEVE_BASE_HLEN - sizeof(struct iphdr)
+               - dev->hard_header_len;
+
+       if (new_mtu < 68)
                return -EINVAL;
+
+       if (new_mtu > max_mtu) {
+               if (strict)
+                       return -EINVAL;
+
+               new_mtu = max_mtu;
+       }
+
        dev->mtu = new_mtu;
        return 0;
 }
 
+static int geneve_change_mtu(struct net_device *dev, int new_mtu)
+{
+       return __geneve_change_mtu(dev, new_mtu, true);
+}
+
 static int geneve_fill_metadata_dst(struct net_device *dev, struct sk_buff *skb)
 {
        struct ip_tunnel_info *info = skb_tunnel_info(skb);
@@ -1459,7 +1476,7 @@ struct net_device *geneve_dev_create_fb(struct net *net, const char *name,
        /* openvswitch users expect packet sizes to be unrestricted,
         * so set the largest MTU we can.
         */
-       err = geneve_change_mtu(dev, IP_MAX_MTU);
+       err = __geneve_change_mtu(dev, IP_MAX_MTU, false);
        if (err)
                goto err;