batman-adv: Revert "use core MTU range checking in misc drivers"

The maximum MTU is defined via the slave devices of an batman-adv
interface. Thus it is not possible to calculate the max_mtu during the
creation of the batman-adv device when no slave devices are attached. Doing
so would for example break non-fragmentation setups which then
(incorrectly) allow an MTU of 1500 even when underlying device cannot
transport 1500 bytes + batman-adv headers.

Checking the dynamically calculated max_mtu via the minimum of the slave
devices MTU during .ndo_change_mtu is also used by the bridge interface.

Cc: Jarod Wilson <jarod@redhat.com>
Fixes: b3e3893e1253 ("net: use core MTU range checking in misc drivers")
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/batman-adv/soft-interface.c b/net/batman-adv/soft-interface.c
index 112679d64be5414055bf32a3dbe0b7412caf29ce..49e16b6e0ba3391f36aa60fdadf756df7058f0ba 100644 (file)
--- a/net/batman-adv/soft-interface.c
+++ b/net/batman-adv/soft-interface.c
@@ -158,6 +158,17 @@ static int batadv_interface_set_mac_addr(struct net_device *dev, void *p)
        return 0;
 }
 
+static int batadv_interface_change_mtu(struct net_device *dev, int new_mtu)
+{
+       /* check ranges */
+       if ((new_mtu < 68) || (new_mtu > batadv_hardif_min_mtu(dev)))
+               return -EINVAL;
+
+       dev->mtu = new_mtu;
+
+       return 0;
+}
+
 /**
  * batadv_interface_set_rx_mode - set the rx mode of a device
  * @dev: registered network device to modify
@@ -909,6 +920,7 @@ static const struct net_device_ops batadv_netdev_ops = {
        .ndo_vlan_rx_add_vid = batadv_interface_add_vid,
        .ndo_vlan_rx_kill_vid = batadv_interface_kill_vid,
        .ndo_set_mac_address = batadv_interface_set_mac_addr,
+       .ndo_change_mtu = batadv_interface_change_mtu,
        .ndo_set_rx_mode = batadv_interface_set_rx_mode,
        .ndo_start_xmit = batadv_interface_tx,
        .ndo_validate_addr = eth_validate_addr,
@@ -975,7 +987,6 @@ struct net_device *batadv_softif_create(struct net *net, const char *name)
        dev_net_set(soft_iface, net);
 
        soft_iface->rtnl_link_ops = &batadv_link_ops;
-       soft_iface->max_mtu = batadv_hardif_min_mtu(soft_iface);
 
        ret = register_netdevice(soft_iface);
        if (ret < 0) {