ethtool: fail closed if we can't get max channel used in indirection tables

Commit 0d1b7d6c ("bnxt: fix crashes when reducing ring count with
active RSS contexts") proves that allowing indirection table to contain
channels with out of bounds IDs may lead to crashes. Currently the
max channel check in the core gets skipped if driver can't fetch
the indirection table or when we can't allocate memory.

Both of those conditions should be extremely rare but if they do
happen we should try to be safe and fail the channel change.
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://patch.msgid.link/20240710174043.754664-2-kuba@kernel.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/ethtool/channels.c

@@ -171,11 +171,9 @@ ethnl_set_channels(struct ethnl_req_info *req_info, struct genl_info *info)
 	 */
 	if (ethtool_get_max_rxnfc_channel(dev, &max_rxnfc_in_use))
 		max_rxnfc_in_use = 0;
-	if (!netif_is_rxfh_configured(dev) ||
-	    ethtool_get_max_rxfh_channel(dev, &max_rxfh_in_use))
-		max_rxfh_in_use = 0;
+	max_rxfh_in_use = ethtool_get_max_rxfh_channel(dev);
 	if (channels.combined_count + channels.rx_count <= max_rxfh_in_use) {
-		GENL_SET_ERR_MSG(info, "requested channel counts are too low for existing indirection table settings");
+		GENL_SET_ERR_MSG_FMT(info, "requested channel counts are too low for existing indirection table (%d)", max_rxfh_in_use);
 		return -EINVAL;
 	}
 	if (channels.combined_count + channels.rx_count <= max_rxnfc_in_use) {

net/ethtool/common.c

@@ -587,35 +587,39 @@ int ethtool_get_max_rxnfc_channel(struct net_device *dev, u64 *max)
 	return err;
 }
 
-int ethtool_get_max_rxfh_channel(struct net_device *dev, u32 *max)
+u32 ethtool_get_max_rxfh_channel(struct net_device *dev)
 {
 	struct ethtool_rxfh_param rxfh = {};
-	u32 dev_size, current_max = 0;
+	u32 dev_size, current_max;
 	int ret;
 
+	if (!netif_is_rxfh_configured(dev))
+		return 0;
+
 	if (!dev->ethtool_ops->get_rxfh_indir_size ||
 	    !dev->ethtool_ops->get_rxfh)
-		return -EOPNOTSUPP;
+		return 0;
 	dev_size = dev->ethtool_ops->get_rxfh_indir_size(dev);
 	if (dev_size == 0)
-		return -EOPNOTSUPP;
+		return 0;
 
 	rxfh.indir = kcalloc(dev_size, sizeof(rxfh.indir[0]), GFP_USER);
 	if (!rxfh.indir)
-		return -ENOMEM;
+		return U32_MAX;
 
 	ret = dev->ethtool_ops->get_rxfh(dev, &rxfh);
-	if (ret)
-		goto out;
+	if (ret) {
+		current_max = U32_MAX;
+		goto out_free;
+	}
 
+	current_max = 0;
 	while (dev_size--)
 		current_max = max(current_max, rxfh.indir[dev_size]);
 
-	*max = current_max;
-
-out:
+out_free:
 	kfree(rxfh.indir);
-	return ret;
+	return current_max;
 }
 
 int ethtool_check_ops(const struct ethtool_ops *ops)

net/ethtool/common.h

@@ -42,7 +42,7 @@ int __ethtool_get_link(struct net_device *dev);
 bool convert_legacy_settings_to_link_ksettings(
 	struct ethtool_link_ksettings *link_ksettings,
 	const struct ethtool_cmd *legacy_settings);
-int ethtool_get_max_rxfh_channel(struct net_device *dev, u32 *max);
+u32 ethtool_get_max_rxfh_channel(struct net_device *dev);
 int ethtool_get_max_rxnfc_channel(struct net_device *dev, u64 *max);
 int __ethtool_get_ts_info(struct net_device *dev, struct ethtool_ts_info *info);
 

net/ethtool/ioctl.c

@@ -2049,9 +2049,7 @@ static noinline_for_stack int ethtool_set_channels(struct net_device *dev,
 	 * indirection table/rxnfc settings */
 	if (ethtool_get_max_rxnfc_channel(dev, &max_rxnfc_in_use))
 		max_rxnfc_in_use = 0;
-	if (!netif_is_rxfh_configured(dev) ||
-	    ethtool_get_max_rxfh_channel(dev, &max_rxfh_in_use))
-		max_rxfh_in_use = 0;
+	max_rxfh_in_use = ethtool_get_max_rxfh_channel(dev);
 	if (channels.combined_count + channels.rx_count <=
 	    max_t(u64, max_rxnfc_in_use, max_rxfh_in_use))
 		return -EINVAL;