Subject: Re: [PATCH net-next v11 09/12] virtio_net: Implement IPv4 ethtool flow rules

From: "Michael S. Tsirkin" <[email-masked]>
Date: Wed, 19 Nov 2025 04:18:42 -0500

On Tue, Nov 18, 2025 at 04:31:09PM -0500, Michael S. Tsirkin wrote:
> > +static int setup_ip_key_mask(struct virtio_net_ff_selector *selector,
> > +			     u8 *key,
> > +			     const struct ethtool_rx_flow_spec *fs)
> > +{
> > +	struct iphdr *v4_m = (struct iphdr *)&selector->mask;
> > +	struct iphdr *v4_k = (struct iphdr *)key;
> > +
> > +	selector->type = VIRTIO_NET_FF_MASK_TYPE_IPV4;
> > +	selector->length = sizeof(struct iphdr);
> > +
> > +	if (fs->h_u.usr_ip4_spec.l4_4_bytes ||
> > +	    fs->h_u.usr_ip4_spec.tos ||
> > +	    fs->h_u.usr_ip4_spec.ip_ver != ETH_RX_NFC_IP4)
> > +		return -EOPNOTSUPP;
> 
> So include/uapi/linux/ethtool.h says:
> 
>  * struct ethtool_usrip4_spec - general flow specification for IPv4
>  * @ip4src: Source host
>  * @ip4dst: Destination host
>  * @l4_4_bytes: First 4 bytes of transport (layer 4) header
>  * @tos: Type-of-service
>  * @ip_ver: Value must be %ETH_RX_NFC_IP4; mask must be 0
>  * @proto: Transport protocol number; mask must be 0
> 
> I guess this ETH_RX_NFC_IP4 check validates that userspace follows this
> documentation? But then shouldn't you check the mask
> as well? and mask for proto?
> 
> 
> 

in fact, what if e.g. tos is 0 but mask is non-zero? should not
this be rejected, too?