Linux Virtualization - Oct 2016 - [PATCH net-next v2 6/9] net: use core MTU range checking in virt drivers

On Thu, Oct 20, 2016 at 11:23:54PM +0300, Michael S. Tsirkin
wrote:
> On Thu, Oct 20, 2016 at 01:55:21PM -0400, Jarod Wilson wrote:
...
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index fad84f3..720809f 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -1419,17 +1419,6 @@ static const struct ethtool_ops
virtnet_ethtool_ops = {
> >  	.set_settings = virtnet_set_settings,
> >  };
> >  
> > -#define MIN_MTU 68
> > -#define MAX_MTU 65535
> > -
> > -static int virtnet_change_mtu(struct net_device *dev, int new_mtu)
> > -{
> > -	if (new_mtu < MIN_MTU || new_mtu > MAX_MTU)
> > -		return -EINVAL;
> > -	dev->mtu = new_mtu;
> > -	return 0;
> > -}
> > -
> >  static const struct net_device_ops virtnet_netdev = {
> >  	.ndo_open            = virtnet_open,
> >  	.ndo_stop   	     = virtnet_close,
> > @@ -1437,7 +1426,6 @@ static const struct net_device_ops
virtnet_netdev = {
> >  	.ndo_validate_addr   = eth_validate_addr,
> >  	.ndo_set_mac_address = virtnet_set_mac_address,
> >  	.ndo_set_rx_mode     = virtnet_set_rx_mode,
> > -	.ndo_change_mtu	     = virtnet_change_mtu,
> >  	.ndo_get_stats64     = virtnet_stats,
> >  	.ndo_vlan_rx_add_vid = virtnet_vlan_rx_add_vid,
> >  	.ndo_vlan_rx_kill_vid = virtnet_vlan_rx_kill_vid,
> > @@ -1748,6 +1736,9 @@ static bool virtnet_validate_features(struct
virtio_device *vdev)
> >  	return true;
> >  }
> >  
> > +#define MIN_MTU ETH_MIN_MTU
> > +#define MAX_MTU ETH_MAX_MTU
> > +
> 
> Can we drop these btw?
Bah. Yeah. Should have just used them directly. I didn't add ETH_MAX_MTU
until after doing the virtio_net changes, so I missed that.
> >  static int virtnet_probe(struct virtio_device *vdev)
> >  {
> >  	int i, err;
> > @@ -1821,6 +1812,10 @@ static int virtnet_probe(struct virtio_device
*vdev)
> >  
> >  	dev->vlan_features = dev->features;
> >  
> > +	/* MTU range: 68 - 65535 */
> > +	dev->min_mtu = MIN_MTU;
> > +	dev->max_mtu = MAX_MTU;
> > +
> >  	/* Configuration may specify what MAC to use.  Otherwise random. */
> >  	if (virtio_has_feature(vdev, VIRTIO_NET_F_MAC))
> >  		virtio_cread_bytes(vdev,
> > @@ -1875,8 +1870,10 @@ static int virtnet_probe(struct virtio_device
*vdev)
> >  		mtu = virtio_cread16(vdev,
> >  				     offsetof(struct virtio_net_config,
> >  					      mtu));
> > -		if (virtnet_change_mtu(dev, mtu))
> > +		if (mtu < dev->min_mtu || mtu > dev->max_mtu)
> 
> In fact the > max_mtu branch does not make sense since a 16 bit
> value can't exceed MAX_MTU.
Hm. mtu is declared as an int, not sure if there's any sort of type
promotion to be worried about (not an area I know much/anything about).
Certainly something that could be looked into as a minor optimization,
though it's only in a probe path and shouldn't hurt anything, so ...
meh?

-- 
Jarod Wilson
jarod at redhat.com

On Thu, Oct 20, 2016 at 10:37:20PM -0400, Jarod Wilson
wrote:
> On Thu, Oct 20, 2016 at 11:23:54PM +0300, Michael S. Tsirkin wrote:
> > On Thu, Oct 20, 2016 at 01:55:21PM -0400, Jarod Wilson wrote:
> ...
> > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > > index fad84f3..720809f 100644
> > > --- a/drivers/net/virtio_net.c
> > > +++ b/drivers/net/virtio_net.c
> > > @@ -1419,17 +1419,6 @@ static const struct ethtool_ops
virtnet_ethtool_ops = {
> > >  	.set_settings = virtnet_set_settings,
> > >  };
> > >  
> > > -#define MIN_MTU 68
> > > -#define MAX_MTU 65535
> > > -
> > > -static int virtnet_change_mtu(struct net_device *dev, int
new_mtu)
> > > -{
> > > -	if (new_mtu < MIN_MTU || new_mtu > MAX_MTU)
> > > -		return -EINVAL;
> > > -	dev->mtu = new_mtu;
> > > -	return 0;
> > > -}
> > > -
> > >  static const struct net_device_ops virtnet_netdev = {
> > >  	.ndo_open            = virtnet_open,
> > >  	.ndo_stop   	     = virtnet_close,
> > > @@ -1437,7 +1426,6 @@ static const struct net_device_ops
virtnet_netdev = {
> > >  	.ndo_validate_addr   = eth_validate_addr,
> > >  	.ndo_set_mac_address = virtnet_set_mac_address,
> > >  	.ndo_set_rx_mode     = virtnet_set_rx_mode,
> > > -	.ndo_change_mtu	     = virtnet_change_mtu,
> > >  	.ndo_get_stats64     = virtnet_stats,
> > >  	.ndo_vlan_rx_add_vid = virtnet_vlan_rx_add_vid,
> > >  	.ndo_vlan_rx_kill_vid = virtnet_vlan_rx_kill_vid,
> > > @@ -1748,6 +1736,9 @@ static bool
virtnet_validate_features(struct virtio_device *vdev)
> > >  	return true;
> > >  }
> > >  
> > > +#define MIN_MTU ETH_MIN_MTU
> > > +#define MAX_MTU ETH_MAX_MTU
> > > +
> > 
> > Can we drop these btw?
> 
> Bah. Yeah. Should have just used them directly. I didn't add
ETH_MAX_MTU
> until after doing the virtio_net changes, so I missed that.
> 
> > >  static int virtnet_probe(struct virtio_device *vdev)
> > >  {
> > >  	int i, err;
> > > @@ -1821,6 +1812,10 @@ static int virtnet_probe(struct
virtio_device *vdev)
> > >  
> > >  	dev->vlan_features = dev->features;
> > >  
> > > +	/* MTU range: 68 - 65535 */
> > > +	dev->min_mtu = MIN_MTU;
> > > +	dev->max_mtu = MAX_MTU;
> > > +
> > >  	/* Configuration may specify what MAC to use.  Otherwise
random. */
> > >  	if (virtio_has_feature(vdev, VIRTIO_NET_F_MAC))
> > >  		virtio_cread_bytes(vdev,
> > > @@ -1875,8 +1870,10 @@ static int virtnet_probe(struct
virtio_device *vdev)
> > >  		mtu = virtio_cread16(vdev,
> > >  				     offsetof(struct virtio_net_config,
> > >  					      mtu));
> > > -		if (virtnet_change_mtu(dev, mtu))
> > > +		if (mtu < dev->min_mtu || mtu > dev->max_mtu)
> > 
> > In fact the > max_mtu branch does not make sense since a 16 bit
> > value can't exceed MAX_MTU.
> 
> Hm. mtu is declared as an int, not sure if there's any sort of type
> promotion to be worried about (not an area I know much/anything about).
Not by design, that's for sure.
> Certainly something that could be looked into as a minor optimization,
> though it's only in a probe path and shouldn't hurt anything, so
... meh?
Right. Aaron said he's working on a patch that essentially does
dev->max_mtu = mtu after validation, so this part will look
a bit silly there.
> -- 
> Jarod Wilson
> jarod at redhat.com

"Michael S. Tsirkin" <mst at redhat.com> writes:
> On Thu, Oct 20, 2016 at 10:37:20PM -0400, Jarod Wilson wrote:
>> On Thu, Oct 20, 2016 at 11:23:54PM +0300, Michael S. Tsirkin wrote:
>> > On Thu, Oct 20, 2016 at 01:55:21PM -0400, Jarod Wilson wrote:
>> ...
>> > > diff --git a/drivers/net/virtio_net.c
b/drivers/net/virtio_net.c
>> > > index fad84f3..720809f 100644
>> > > --- a/drivers/net/virtio_net.c
>> > > +++ b/drivers/net/virtio_net.c
>> > > @@ -1419,17 +1419,6 @@ static const struct ethtool_ops
virtnet_ethtool_ops = {
>> > >  	.set_settings = virtnet_set_settings,
>> > >  };
>> > >  
>> > > -#define MIN_MTU 68
>> > > -#define MAX_MTU 65535
>> > > -
>> > > -static int virtnet_change_mtu(struct net_device *dev, int
new_mtu)
>> > > -{
>> > > -	if (new_mtu < MIN_MTU || new_mtu > MAX_MTU)
>> > > -		return -EINVAL;
>> > > -	dev->mtu = new_mtu;
>> > > -	return 0;
>> > > -}
>> > > -
>> > >  static const struct net_device_ops virtnet_netdev = {
>> > >  	.ndo_open            = virtnet_open,
>> > >  	.ndo_stop   	     = virtnet_close,
>> > > @@ -1437,7 +1426,6 @@ static const struct net_device_ops
virtnet_netdev = {
>> > >  	.ndo_validate_addr   = eth_validate_addr,
>> > >  	.ndo_set_mac_address = virtnet_set_mac_address,
>> > >  	.ndo_set_rx_mode     = virtnet_set_rx_mode,
>> > > -	.ndo_change_mtu	     = virtnet_change_mtu,
>> > >  	.ndo_get_stats64     = virtnet_stats,
>> > >  	.ndo_vlan_rx_add_vid = virtnet_vlan_rx_add_vid,
>> > >  	.ndo_vlan_rx_kill_vid = virtnet_vlan_rx_kill_vid,
>> > > @@ -1748,6 +1736,9 @@ static bool
virtnet_validate_features(struct virtio_device *vdev)
>> > >  	return true;
>> > >  }
>> > >  
>> > > +#define MIN_MTU ETH_MIN_MTU
>> > > +#define MAX_MTU ETH_MAX_MTU
>> > > +
>> > 
>> > Can we drop these btw?
>> 
>> Bah. Yeah. Should have just used them directly. I didn't add
ETH_MAX_MTU
>> until after doing the virtio_net changes, so I missed that.
>> 
>> > >  static int virtnet_probe(struct virtio_device *vdev)
>> > >  {
>> > >  	int i, err;
>> > > @@ -1821,6 +1812,10 @@ static int virtnet_probe(struct
virtio_device *vdev)
>> > >  
>> > >  	dev->vlan_features = dev->features;
>> > >  
>> > > +	/* MTU range: 68 - 65535 */
>> > > +	dev->min_mtu = MIN_MTU;
>> > > +	dev->max_mtu = MAX_MTU;
>> > > +
>> > >  	/* Configuration may specify what MAC to use.  Otherwise
random. */
>> > >  	if (virtio_has_feature(vdev, VIRTIO_NET_F_MAC))
>> > >  		virtio_cread_bytes(vdev,
>> > > @@ -1875,8 +1870,10 @@ static int virtnet_probe(struct
virtio_device *vdev)
>> > >  		mtu = virtio_cread16(vdev,
>> > >  				     offsetof(struct virtio_net_config,
>> > >  					      mtu));
>> > > -		if (virtnet_change_mtu(dev, mtu))
>> > > +		if (mtu < dev->min_mtu || mtu > dev->max_mtu)
>> > 
>> > In fact the > max_mtu branch does not make sense since a 16 bit
>> > value can't exceed MAX_MTU.
>> 
>> Hm. mtu is declared as an int, not sure if there's any sort of type
>> promotion to be worried about (not an area I know much/anything about).
>
> Not by design, that's for sure.
If you're really worried, we could declare it as a u16. The value
returned from virtio_cread16 is type u16, and there are no type
promotion rules I'm aware of that would do the wrong thing there.
>> Certainly something that could be looked into as a minor optimization,
>> though it's only in a probe path and shouldn't hurt anything,
so ... meh?
>
> Right. Aaron said he's working on a patch that essentially does
> dev->max_mtu = mtu after validation, so this part will look
> a bit silly there.
Agreed, but I can do that in my patch if you don't want the extra churn.

-Aaron