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

@@ -973,32 +973,35 @@ 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;
 
-	rc = ops->get_rxfh(dev, &rxfh);
-	if (rc)
-		return rc;
+	if (ops->get_rxfh) {
+		struct ethtool_rxfh_param rxfh = {};
 
-	/* Sanity check: if symmetric-xor is set, then:
-	 * 1 - no other fields besides IP src/dst and/or L4 src/dst
-	 * 2 - If src is set, dst must also be set
-	 */
-	if ((rxfh.input_xfrm & RXH_XFRM_SYM_XOR) &&
-	    ((info.data & ~(RXH_IP_SRC | RXH_IP_DST |
-			    RXH_L4_B_0_1 | RXH_L4_B_2_3)) ||
-	     (!!(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->get_rxfh(dev, &rxfh);
+		if (rc)
+			return rc;
+
+		/* Sanity check: if symmetric-xor is set, then:
+		 * 1 - no other fields besides IP src/dst and/or L4 src/dst
+		 * 2 - If src is set, dst must also be set
+		 */
+		if ((rxfh.input_xfrm & RXH_XFRM_SYM_XOR) &&
+		    ((info.data & ~(RXH_IP_SRC | RXH_IP_DST |
+				    RXH_L4_B_0_1 | RXH_L4_B_2_3)) ||
+		     (!!(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)