net: vxlan: use custom ndo_change_mtu handler

When adding a new vxlan device to an "underlying carrier" (here:
dst->remote_ifindex), the MTU size assigned to the vxlan device
is the MTU at setup time of the carrier - needed headroom, when
adding a vxlan device w/o explicit carrier, then it defaults
to 1500.

In case of an explicit carrier that supports jumbo frames, we
currently cannot change vxlan MTU via ip(8) to > 1500 in
post-setup time, as vxlan driver uses eth_change_mtu() as default
method for manually setting MTU.

Hence, use a custom implementation that only falls back to
eth_change_mtu() in case we didn't use a dev parameter on device
setup time, and otherwise allow a max MTU setting of the carrier
incl. adjustment for headroom.

Reported-by: Shahed Shaikh <shahed.shaikh@qlogic.com>
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Acked-by: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 24 insertions, 1 deletions

diff --git a/drivers/net/vxlan.c b/drivers/net/vxlan.c
index ea203c1aaa24..aef44aa44fe3 100644
--- a/drivers/net/vxlan.c
+++ b/drivers/net/vxlan.c
@@ -2014,6 +2014,29 @@ static void vxlan_set_multicast_list(struct net_device *dev)
 {
 }
 
+static int vxlan_change_mtu(struct net_device *dev, int new_mtu)
+{
+        struct vxlan_dev *vxlan = netdev_priv(dev);
+        struct vxlan_rdst *dst = &vxlan->default_dst;
+        struct net_device *lowerdev;
+        int max_mtu;
+
+        lowerdev = __dev_get_by_index(dev_net(dev), dst->remote_ifindex);
+        if (lowerdev == NULL)
+                return eth_change_mtu(dev, new_mtu);
+
+        if (dst->remote_ip.sa.sa_family == AF_INET6)
+                max_mtu = lowerdev->mtu - VXLAN6_HEADROOM;
+        else
+                max_mtu = lowerdev->mtu - VXLAN_HEADROOM;
+
+        if (new_mtu < 68 || new_mtu > max_mtu)
+                return -EINVAL;
+
+        dev->mtu = new_mtu;
+        return 0;
+}
+
 static const struct net_device_ops vxlan_netdev_ops = {
         .ndo_init               = vxlan_init,
         .ndo_uninit             = vxlan_uninit,
@@ -2022,7 +2045,7 @@ static const struct net_device_ops vxlan_netdev_ops = {
         .ndo_start_xmit         = vxlan_xmit,
         .ndo_get_stats64        = ip_tunnel_get_stats64,
         .ndo_set_rx_mode        = vxlan_set_multicast_list,
-        .ndo_change_mtu         = eth_change_mtu,
+        .ndo_change_mtu         = vxlan_change_mtu,
         .ndo_validate_addr      = eth_validate_addr,
         .ndo_set_mac_address    = eth_mac_addr,
         .ndo_fdb_add            = vxlan_fdb_add,