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

From: "Michael S. Tsirkin" <[email-masked]>
Date: Tue, 18 Nov 2025 16:31:05 -0500

On Tue, Nov 18, 2025 at 08:38:59AM -0600, Daniel Jurgens wrote:
> Add support for IP_USER type rules from ethtool.
> 
> Example:
> $ ethtool -U ens9 flow-type ip4 src-ip 192.168.51.101 action -1
> Added rule with ID 1
> 
> The example rule will drop packets with the source IP specified.
> 
> Signed-off-by: Daniel Jurgens <[email-masked]>
> Reviewed-by: Parav Pandit <[email-masked]>
> Reviewed-by: Shahar Shitrit <[email-masked]>
> Reviewed-by: Xuan Zhuo <[email-masked]>
> ---
> v4:
>     - Fixed bug in protocol check of parse_ip4
>     - (u8 *) to (void *) casting.
>     - Alignment issues.
> ---
>  drivers/net/virtio_net.c | 122 ++++++++++++++++++++++++++++++++++++---
>  1 file changed, 115 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index f392ea30f2c7..c1adba60b6a8 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -6904,6 +6904,34 @@ static bool validate_eth_mask(const struct virtnet_ff *ff,
>  	return true;
>  }
>  
> +static bool validate_ip4_mask(const struct virtnet_ff *ff,
> +			      const struct virtio_net_ff_selector *sel,
> +			      const struct virtio_net_ff_selector *sel_cap)
> +{
> +	bool partial_mask = !!(sel_cap->flags & VIRTIO_NET_FF_MASK_F_PARTIAL_MASK);
> +	struct iphdr *cap, *mask;
> +
> +	cap = (struct iphdr *)&sel_cap->mask;
> +	mask = (struct iphdr *)&sel->mask;
> +
> +	if (mask->saddr &&
> +	    !check_mask_vs_cap(&mask->saddr, &cap->saddr,
> +			       sizeof(__be32), partial_mask))
> +		return false;
> +
> +	if (mask->daddr &&
> +	    !check_mask_vs_cap(&mask->daddr, &cap->daddr,
> +			       sizeof(__be32), partial_mask))
> +		return false;
> +
> +	if (mask->protocol &&
> +	    !check_mask_vs_cap(&mask->protocol, &cap->protocol,
> +			       sizeof(u8), partial_mask))
> +		return false;
> +
> +	return true;
> +}
> +
>  static bool validate_mask(const struct virtnet_ff *ff,
>  			  const struct virtio_net_ff_selector *sel)
>  {
> @@ -6915,11 +6943,36 @@ static bool validate_mask(const struct virtnet_ff *ff,
>  	switch (sel->type) {
>  	case VIRTIO_NET_FF_MASK_TYPE_ETH:
>  		return validate_eth_mask(ff, sel, sel_cap);
> +
> +	case VIRTIO_NET_FF_MASK_TYPE_IPV4:
> +		return validate_ip4_mask(ff, sel, sel_cap);
>  	}
>  
>  	return false;
>  }
>  
> +static void parse_ip4(struct iphdr *mask, struct iphdr *key,
> +		      const struct ethtool_rx_flow_spec *fs)
> +{
> +	const struct ethtool_usrip4_spec *l3_mask = &fs->m_u.usr_ip4_spec;
> +	const struct ethtool_usrip4_spec *l3_val  = &fs->h_u.usr_ip4_spec;
> +
> +	mask->saddr = l3_mask->ip4src;
> +	mask->daddr = l3_mask->ip4dst;
> +	key->saddr = l3_val->ip4src;
> +	key->daddr = l3_val->ip4dst;
> +
> +	if (l3_mask->proto) {

you seem to check mask for proto here but the ethtool_usrip4_spec doc
seems to say the mask for proto must be 0. 

what gives?

> +		mask->protocol = l3_mask->proto;
> +		key->protocol = l3_val->proto;
> +	}
> +}
> +
> +static bool has_ipv4(u32 flow_type)
> +{
> +	return flow_type == IP_USER_FLOW;
> +}
> +
>  static int setup_classifier(struct virtnet_ff *ff,
>  			    struct virtnet_classifier **c)
>  {
> @@ -7054,6 +7107,7 @@ static bool supported_flow_type(const struct ethtool_rx_flow_spec *fs)
>  {
>  	switch (fs->flow_type) {
>  	case ETHER_FLOW:
> +	case IP_USER_FLOW:
>  		return true;
>  	}
>  
> @@ -7082,11 +7136,23 @@ static int validate_flow_input(struct virtnet_ff *ff,
>  }
>  
>  static void calculate_flow_sizes(struct ethtool_rx_flow_spec *fs,
> -				 size_t *key_size, size_t *classifier_size,
> -				 int *num_hdrs)
> +				size_t *key_size, size_t *classifier_size,
> +				int *num_hdrs)
>  {
> +	size_t size = sizeof(struct ethhdr);
> +
>  	*num_hdrs = 1;
>  	*key_size = sizeof(struct ethhdr);

So *key_size  is assigned here ...

> +
> +	if (fs->flow_type == ETHER_FLOW)
> +		goto done;
> +
> +	++(*num_hdrs);
> +	if (has_ipv4(fs->flow_type))
> +		size += sizeof(struct iphdr);
> +

... never used

> +done:
> +	*key_size = size;

and over-written here.

what is going on here, is that this is spaghetti code
misusing goto for if instructions which obscures the flow.

It should be if (fs->flow_type != ETHER_FLOW) {

	... rest of code ...
}

and then it will be clear doing *key_size = size once is enough.

>  	/*
>  	 * The classifier size is the size of the classifier header, a selector
>  	 * header for each type of header in the match criteria, and each header
> @@ -7098,8 +7164,9 @@ static void calculate_flow_sizes(struct ethtool_rx_flow_spec *fs,
>  }
>  
>  static void setup_eth_hdr_key_mask(struct virtio_net_ff_selector *selector,
> -				   u8 *key,
> -				   const struct ethtool_rx_flow_spec *fs)
> +				  u8 *key,
> +				  const struct ethtool_rx_flow_spec *fs,
> +				  int num_hdrs)
>  {
>  	struct ethhdr *eth_m = (struct ethhdr *)&selector->mask;
>  	struct ethhdr *eth_k = (struct ethhdr *)key;
> @@ -7107,8 +7174,33 @@ static void setup_eth_hdr_key_mask(struct virtio_net_ff_selector *selector,
>  	selector->type = VIRTIO_NET_FF_MASK_TYPE_ETH;
>  	selector->length = sizeof(struct ethhdr);
>  
> -	memcpy(eth_m, &fs->m_u.ether_spec, sizeof(*eth_m));
> -	memcpy(eth_k, &fs->h_u.ether_spec, sizeof(*eth_k));
> +	if (num_hdrs > 1) {
> +		eth_m->h_proto = cpu_to_be16(0xffff);
> +		eth_k->h_proto = cpu_to_be16(ETH_P_IP);
> +	} else {
> +		memcpy(eth_m, &fs->m_u.ether_spec, sizeof(*eth_m));
> +		memcpy(eth_k, &fs->h_u.ether_spec, sizeof(*eth_k));
> +	}
> +}
> +
> +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?

> +
> +	parse_ip4(v4_m, v4_k, fs);
> +
> +	return 0;
>  }
>  
>  static int
> @@ -7130,6 +7222,13 @@ validate_classifier_selectors(struct virtnet_ff *ff,
>  	return 0;
>  }
>  
> +static
> +struct virtio_net_ff_selector *next_selector(struct virtio_net_ff_selector *sel)
> +{
> +	return (void *)sel + sizeof(struct virtio_net_ff_selector) +
> +		sel->length;
> +}
> +
>  static int build_and_insert(struct virtnet_ff *ff,
>  			    struct virtnet_ethtool_rule *eth_rule)
>  {
> @@ -7167,8 +7266,17 @@ static int build_and_insert(struct virtnet_ff *ff,
>  	classifier->count = num_hdrs;
>  	selector = (void *)&classifier->selectors[0];
>  
> -	setup_eth_hdr_key_mask(selector, key, fs);
> +	setup_eth_hdr_key_mask(selector, key, fs, num_hdrs);
> +	if (num_hdrs == 1)
> +		goto validate;

Please stop abusing goto's for if.
this is not error handling, not breaking out of loops ...

please do not.

> +
> +	selector = next_selector(selector);
> +
> +	err = setup_ip_key_mask(selector, key + sizeof(struct ethhdr), fs);
> +	if (err)
> +		goto err_classifier;
>  
> +validate:
>  	err = validate_classifier_selectors(ff, classifier, num_hdrs);
>  	if (err)
>  		goto err_key;
> -- 
> 2.50.1