net: ethtool: Handle missing cable test TDR parameters

A last minute change put the TDR cable test parameters into a nest.
The validation is not sufficient, resulting in an oops if the nest is
missing. Set default values first, then update them if the nest is
provided.

Fixes: f2bc8ad31a ("net: ethtool: Allow PHY cable test TDR data to configured")
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ethtool/cabletest.c

@@ -234,6 +234,14 @@ static int ethnl_act_cable_test_tdr_cfg(const struct nlattr *nest,
 	struct nlattr *tb[ETHTOOL_A_CABLE_TEST_TDR_CFG_MAX + 1];
 	int ret;
 
+	cfg->first = 100;
+	cfg->step = 100;
+	cfg->last = MAX_CABLE_LENGTH_CM;
+	cfg->pair = PHY_PAIR_ALL;
+
+	if (!nest)
+		return 0;
+
 	ret = nla_parse_nested(tb, ETHTOOL_A_CABLE_TEST_TDR_CFG_MAX, nest,
 			       cable_test_tdr_act_cfg_policy, info->extack);
 	if (ret < 0)
@@ -242,17 +250,12 @@ static int ethnl_act_cable_test_tdr_cfg(const struct nlattr *nest,
 	if (tb[ETHTOOL_A_CABLE_TEST_TDR_CFG_FIRST])
 		cfg->first = nla_get_u32(
 			tb[ETHTOOL_A_CABLE_TEST_TDR_CFG_FIRST]);
-	else
-		cfg->first = 100;
+
 	if (tb[ETHTOOL_A_CABLE_TEST_TDR_CFG_LAST])
 		cfg->last = nla_get_u32(tb[ETHTOOL_A_CABLE_TEST_TDR_CFG_LAST]);
-	else
-		cfg->last = MAX_CABLE_LENGTH_CM;
 
 	if (tb[ETHTOOL_A_CABLE_TEST_TDR_CFG_STEP])
 		cfg->step = nla_get_u32(tb[ETHTOOL_A_CABLE_TEST_TDR_CFG_STEP]);
-	else
-		cfg->step = 100;
 
 	if (tb[ETHTOOL_A_CABLE_TEST_TDR_CFG_PAIR]) {
 		cfg->pair = nla_get_u8(tb[ETHTOOL_A_CABLE_TEST_TDR_CFG_PAIR]);
@@ -263,8 +266,6 @@ static int ethnl_act_cable_test_tdr_cfg(const struct nlattr *nest,
 				"invalid pair parameter");
 			return -EINVAL;
 		}
-	} else {
-		cfg->pair = PHY_PAIR_ALL;
 	}
 
 	if (cfg->first > MAX_CABLE_LENGTH_CM) {