Subject: Re: [PATCH] macvtap: Correctly set tap features when IFF_VNET_HDR is disabled.

From: "Michael S. Tsirkin" <[email-masked]>
Date: Wed, 14 Aug 2013 15:10:43 +0300

On Tue, Aug 13, 2013 at 01:55:58PM -0400, Vlad Yasevich wrote:
> When the user turns off IFF_VNET_HDR flag, attempts to change
> offload features via TUNSETOFFLOAD do not work.  This could cause
> GSO packets to be delivered to the user when the user is
> not prepared to handle them.
> 
> To solve, allow processing of TUNSETOFFLOAD when IFF_VNET_HDR is
> disabled and make sure to turn off all offloads in this case.
> Also, when IFF_VNET_HDR is disabled, run throught the offload change
> as well to make sure that the functionality is not dependent on
> the order of the ioclt() calls.
> 
> Signed-off-by: Vlad Yasevich <[email-masked]>

Hmm, this seems to make it even messier.
So
	set TUNSETOFFLOAD
	clear IFF_VNET_HDR
	set IFF_VNET_HDR

offloads are now clear?

I'm also not sure userspace that sets offloads but clears
vnet hdr knows what it's doing.

How about we fail attempts to clear vnet hdr
unless offloads are disabled?

> ---
>  drivers/net/macvtap.c | 27 +++++++++++++++++++--------
>  1 file changed, 19 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
> index a98fb0e..076b9e7 100644
> --- a/drivers/net/macvtap.c
> +++ b/drivers/net/macvtap.c
> @@ -1019,6 +1019,7 @@ static int set_offload(struct macvtap_queue *q, unsigned long arg)
>  	struct macvlan_dev *vlan;
>  	netdev_features_t features;
>  	netdev_features_t feature_mask = 0;
> +	netdev_features_t tap_mask = TUN_OFFLOADS;
>  
>  	vlan = rtnl_dereference(q->vlan);
>  	if (!vlan)
> @@ -1026,7 +1027,12 @@ static int set_offload(struct macvtap_queue *q, unsigned long arg)
>  
>  	features = vlan->dev->features;
>  
> -	if (arg & TUN_F_CSUM) {
> +	if (!(q->flags & IFF_VNET_HDR)) {
> +		/* Turn off all checsum offloading also if user does
> +		 * not user vnet_hdr.

Does not set?

> +		 */
> +		tap_mask |= NETIF_F_ALL_CSUM;
> +	} else if (arg & TUN_F_CSUM) {
>  		feature_mask = NETIF_F_HW_CSUM;
>  
>  		if (arg & (TUN_F_TSO4 | TUN_F_TSO6)) {
> @@ -1058,8 +1064,7 @@ static int set_offload(struct macvtap_queue *q, unsigned long arg)
>  	/* tap_features are the same as features on tun/tap and
>  	 * reflect user expectations.
>  	 */
> -	vlan->tap_features = vlan->dev->features &
> -			    (feature_mask | ~TUN_OFFLOADS);
> +	vlan->tap_features = vlan->dev->features & (feature_mask | ~tap_mask);
>  	vlan->set_features = features;
>  	netdev_update_features(vlan->dev);
>  
> @@ -1092,8 +1097,18 @@ static long macvtap_ioctl(struct file *file, unsigned int cmd,
>  		if ((u & ~(IFF_VNET_HDR | IFF_MULTI_QUEUE)) !=
>  		    (IFF_NO_PI | IFF_TAP))
>  			ret = -EINVAL;
> -		else
> +		else {
> +			if ((q->flags ^ u) & IFF_VNET_HDR) {
> +				/* vnet_hdr support impacts the offloads,
> +				 * so we need to run throught the offload

throught ?

> +				 * change.
> +				 */
> +				rtnl_lock();
> +				ret = set_offload(q, 0);
> +				rtnl_unlock();
> +			}
>  			q->flags = u;
> +		}
>  
>  		return ret;
>  
> @@ -1155,10 +1170,6 @@ static long macvtap_ioctl(struct file *file, unsigned int cmd,
>  			    TUN_F_TSO_ECN | TUN_F_UFO))
>  			return -EINVAL;
>  
> -		/* TODO: only accept frames with the features that
> -			 got enabled for forwarded frames */
> -		if (!(q->flags & IFF_VNET_HDR))
> -			return  -EINVAL;
>  		rtnl_lock();
>  		ret = set_offload(q, arg);
>  		rtnl_unlock();
> -- 
> 1.8.1.4