Subject: Re: [PATCH net-next 4/6] net: use core MTU range checking in core net infra

From: Jarod Wilson <[email-masked]>
Date: Wed, 19 Oct 2016 10:40:06 -0400

On Wed, Oct 19, 2016 at 03:55:29PM +0200, Sabrina Dubroca wrote:
> 2016-10-18, 22:33:31 -0400, Jarod Wilson wrote:
> > geneve:
> > - Merge __geneve_change_mtu back into geneve_change_mtu, set max_mtu
> > - This one isn't quite as straight-forward as others, could use some
> >   closer inspection and testing
> > 
> > macvlan:
> > - set min/max_mtu
> > 
> > tun:
> > - set min/max_mtu, remove tun_net_change_mtu
> > 
> > vxlan:
> > - Merge __vxlan_change_mtu back into vxlan_change_mtu, set min/max_mtu
> > - This one is also not as straight-forward and could use closer inspection
> >   and testing from vxlan folks
> > 
> > bridge:
> > - set max_mtu via br_min_mtu()
> > 
> > openvswitch:
> > - set min/max_mtu, remove internal_dev_change_mtu
> > - note: max_mtu wasn't checked previously, it's been set to 65535, which
> >   is the largest possible size supported
> > 
> > sch_teql:
> > - set min/max_mtu (note: max_mtu previously unchecked, used max of 65535)
> 
> Nothing for other virtual netdevices? (dummy, veth, bond, etc) Their
> MTU is limited to 1500 now.  Also missing macsec and ip_gre, probably
> others that are using ether_setup.

Yeah, I've clearly missed more than I thought. Doing another sweep now.
I'm thinking more and more that we ought to back out the patch that sets
min/max in ether_setup, save it for last, after we're sure everyone that
calls it has been prepared.

> [...]
> > diff --git a/net/bridge/br_device.c b/net/bridge/br_device.c
> > index 89a687f..81fc79a 100644
> > --- a/net/bridge/br_device.c
> > +++ b/net/bridge/br_device.c
> > @@ -184,17 +184,15 @@ static struct rtnl_link_stats64 *br_get_stats64(struct net_device *dev,
> >  
> >  static int br_change_mtu(struct net_device *dev, int new_mtu)
> >  {
> > +#if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
> >  	struct net_bridge *br = netdev_priv(dev);
> > -	if (new_mtu < 68 || new_mtu > br_min_mtu(br))
> > -		return -EINVAL;
> > -
> > -	dev->mtu = new_mtu;
> >  
> > -#if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
> >  	/* remember the MTU in the rtable for PMTU */
> >  	dst_metric_set(&br->fake_rtable.dst, RTAX_MTU, new_mtu);
> >  #endif
> >  
> > +	dev->mtu = new_mtu;
> > +
> >  	return 0;
> >  }
> >  
> > @@ -390,6 +388,7 @@ void br_dev_setup(struct net_device *dev)
> >  	dev->hw_features = COMMON_FEATURES | NETIF_F_HW_VLAN_CTAG_TX |
> >  			   NETIF_F_HW_VLAN_STAG_TX;
> >  	dev->vlan_features = COMMON_FEATURES;
> > +	dev->max_mtu = br_min_mtu(br);
> 
> br_min_mtu uses br->port_list, which is only initialized a few lines
> later (right after the spin_lock_init() at the end of the context of
> this diff).

Ah, okay, I'd just grouped it with the other dev->foo settings.

> Besides, I don't think this works: br_min_mtu(br) changes when you add
> and remove ports, or when you change the MTU of an enslaved
> device. But this makes the max MTU for the bridge fixed (to 1500).

Okay, how about this: set no max_mtu (or set it to IP_MAX_MTU/65535), and
then retain a check against the possibly ever-changing br_min_mtu(br) in
br_change_mtu()?

> > diff --git a/net/openvswitch/vport-internal_dev.c b/net/openvswitch/vport-internal_dev.c
> > index e7da290..d5d6cae 100644
> > --- a/net/openvswitch/vport-internal_dev.c
> > +++ b/net/openvswitch/vport-internal_dev.c
> > @@ -89,15 +89,6 @@ static const struct ethtool_ops internal_dev_ethtool_ops = {
> >  	.get_link	= ethtool_op_get_link,
> >  };
> >  
> > -static int internal_dev_change_mtu(struct net_device *netdev, int new_mtu)
> > -{
> > -	if (new_mtu < 68)
> > -		return -EINVAL;
> > -
> > -	netdev->mtu = new_mtu;
> > -	return 0;
> > -}
> > -
> >  static void internal_dev_destructor(struct net_device *dev)
> >  {
> >  	struct vport *vport = ovs_internal_dev_get_vport(dev);
> > @@ -148,7 +139,6 @@ static const struct net_device_ops internal_dev_netdev_ops = {
> >  	.ndo_stop = internal_dev_stop,
> >  	.ndo_start_xmit = internal_dev_xmit,
> >  	.ndo_set_mac_address = eth_mac_addr,
> > -	.ndo_change_mtu = internal_dev_change_mtu,
> >  	.ndo_get_stats64 = internal_get_stats,
> >  	.ndo_set_rx_headroom = internal_set_rx_headroom,
> >  };
> 
> vport-internal uses ether_setup, so the MTU is currently limited to
> 1500, no?

Yeah. Sweep ongoing...

-- 
Jarod Wilson
[email-masked]