net: ethtool: Fix symmetric-xor RSS RX flow hash check

Commit 13e59344 ("net: ethtool: add support for symmetric-xor RSS hash")
adds a check to the ethtool set_rxnfc operation, which checks the RX
flow hash if the flag RXH_XFRM_SYM_XOR is set. This flag is introduced
with the same commit. It calls the ethtool get_rxfh operation to get the
RX flow hash data. If get_rxfh is not supported, then EOPNOTSUPP is
returned.

There are driver like tsnep, macb, asp2, genet, gianfar, mtk, ... which
support the ethtool operation set_rxnfc but not get_rxfh. This results
in EOPNOTSUPP returned by ethtool_set_rxnfc() without actually calling
the ethtool operation set_rxnfc. Thus, set_rxnfc got broken for all
these drivers.

Check RX flow hash in ethtool_set_rxnfc() only if driver supports RX
flow hash.

Fixes: 13e59344 ("net: ethtool: add support for symmetric-xor RSS hash")
Signed-off-by: Gerhard Engleder <gerhard@engleder-embedded.com>
Reviewed-by: Ravi Gunasekaran <r-gunasekaran@ti.com>
Link: https://lore.kernel.org/r/20231226205536.32003-1-gerhard@engleder-embedded.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/ethtool/ioctl.c

@@ -973,18 +973,20 @@ static noinline_for_stack int ethtool_set_rxnfc(struct net_device *dev,
 						u32 cmd, void __user *useraddr)
 {
 	const struct ethtool_ops *ops = dev->ethtool_ops;
-	struct ethtool_rxfh_param rxfh = {};
 	struct ethtool_rxnfc info;
 	size_t info_size = sizeof(info);
 	int rc;
 
-	if (!ops->set_rxnfc || !ops->get_rxfh)
+	if (!ops->set_rxnfc)
 		return -EOPNOTSUPP;
 
 	rc = ethtool_rxnfc_copy_struct(cmd, &info, &info_size, useraddr);
 	if (rc)
 		return rc;
 
+	if (ops->get_rxfh) {
+		struct ethtool_rxfh_param rxfh = {};
+
 		rc = ops->get_rxfh(dev, &rxfh);
 		if (rc)
 			return rc;
@@ -999,6 +1001,7 @@ static noinline_for_stack int ethtool_set_rxnfc(struct net_device *dev,
 		     (!!(info.data & RXH_IP_SRC) ^ !!(info.data & RXH_IP_DST)) ||
 		     (!!(info.data & RXH_L4_B_0_1) ^ !!(info.data & RXH_L4_B_2_3))))
 			return -EINVAL;
+	}
 
 	rc = ops->set_rxnfc(dev, &info);
 	if (rc)