ethtool: check if there is at least one channel for TX/RX in the core

Having a channel config with no ability to RX or TX traffic is
clearly wrong. Check for this in the core so the drivers don't
have to.
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Michal Kubecek <mkubecek@suse.cz>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ethtool/channels.c

@@ -129,13 +129,13 @@ int ethnl_set_channels(struct sk_buff *skb, struct genl_info *info)
 {
 	struct nlattr *tb[ETHTOOL_A_CHANNELS_MAX + 1];
 	unsigned int from_channel, old_total, i;
+	bool mod = false, mod_combined = false;
 	struct ethtool_channels channels = {};
 	struct ethnl_req_info req_info = {};
 	const struct nlattr *err_attr;
 	const struct ethtool_ops *ops;
 	struct net_device *dev;
 	u32 max_rx_in_use = 0;
-	bool mod = false;
 	int ret;
 
 	ret = nlmsg_parse(info->nlhdr, GENL_HDRLEN, tb,
@@ -170,7 +170,8 @@ int ethnl_set_channels(struct sk_buff *skb, struct genl_info *info)
 	ethnl_update_u32(&channels.other_count,
 			 tb[ETHTOOL_A_CHANNELS_OTHER_COUNT], &mod);
 	ethnl_update_u32(&channels.combined_count,
-			 tb[ETHTOOL_A_CHANNELS_COMBINED_COUNT], &mod);
+			 tb[ETHTOOL_A_CHANNELS_COMBINED_COUNT], &mod_combined);
+	mod |= mod_combined;
 	ret = 0;
 	if (!mod)
 		goto out_ops;
@@ -193,6 +194,21 @@ int ethnl_set_channels(struct sk_buff *skb, struct genl_info *info)
 		goto out_ops;
 	}
 
+	/* ensure there is at least one RX and one TX channel */
+	if (!channels.combined_count && !channels.rx_count)
+		err_attr = tb[ETHTOOL_A_CHANNELS_RX_COUNT];
+	else if (!channels.combined_count && !channels.tx_count)
+		err_attr = tb[ETHTOOL_A_CHANNELS_TX_COUNT];
+	else
+		err_attr = NULL;
+	if (err_attr) {
+		if (mod_combined)
+			err_attr = tb[ETHTOOL_A_CHANNELS_COMBINED_COUNT];
+		ret = -EINVAL;
+		NL_SET_ERR_MSG_ATTR(info->extack, err_attr, "requested channel counts would result in no RX or TX channel being configured");
+		goto out_ops;
+	}
+
 	/* ensure the new Rx count fits within the configured Rx flow
 	 * indirection table settings
 	 */

net/ethtool/ioctl.c

@@ -1676,6 +1676,11 @@ static noinline_for_stack int ethtool_set_channels(struct net_device *dev,
 	    channels.other_count > curr.max_other)
 		return -EINVAL;
 
+	/* ensure there is at least one RX and one TX channel */
+	if (!channels.combined_count &&
+	    (!channels.rx_count || !channels.tx_count))
+		return -EINVAL;
+
 	/* ensure the new Rx count fits within the configured Rx flow
 	 * indirection table settings */
 	if (netif_is_rxfh_configured(dev) &&