net: ethtool: netlink: Allow NULL nlattrs when getting a phy_device

ethnl_req_get_phydev() is used to lookup a phy_device, in the case an
ethtool netlink command targets a specific phydev within a netdev's
topology.

It takes as a parameter a const struct nlattr *header that's used for
error handling :

       if (!phydev) {
               NL_SET_ERR_MSG_ATTR(extack, header,
                                   "no phy matching phyindex");
               return ERR_PTR(-ENODEV);
       }

In the notify path after a ->set operation however, there's no request
attributes available.

The typical callsite for the above function looks like:

	phydev = ethnl_req_get_phydev(req_base, tb[ETHTOOL_A_XXX_HEADER],
				      info->extack);

So, when tb is NULL (such as in the ethnl notify path), we have a nice
crash.

It turns out that there's only the PLCA command that is in that case, as
the other phydev-specific commands don't have a notification.

This commit fixes the crash by passing the cmd index and the nlattr
array separately, allowing NULL-checking it directly inside the helper.

Fixes: c15e065 ("net: ethtool: Allow passing a phy index for some commands")
Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Reviewed-by: Kory Maincent <kory.maincent@bootlin.com>
Reported-by: Parthiban Veerasooran <parthiban.veerasooran@microchip.com>
Link: https://patch.msgid.link/20250301141114.97204-1-maxime.chevallier@bootlin.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: minimaxwell

net/ethtool/cabletest.c

@@ -72,8 +72,8 @@ int ethnl_act_cable_test(struct sk_buff *skb, struct genl_info *info)
 	dev = req_info.dev;
 
 	rtnl_lock();
-	phydev = ethnl_req_get_phydev(&req_info,
-				      tb[ETHTOOL_A_CABLE_TEST_HEADER],
+	phydev = ethnl_req_get_phydev(&req_info, tb,
+				      ETHTOOL_A_CABLE_TEST_HEADER,
 				      info->extack);
 	if (IS_ERR_OR_NULL(phydev)) {
 		ret = -EOPNOTSUPP;
@@ -339,8 +339,8 @@ int ethnl_act_cable_test_tdr(struct sk_buff *skb, struct genl_info *info)
 		goto out_dev_put;
 
 	rtnl_lock();
-	phydev = ethnl_req_get_phydev(&req_info,
-				      tb[ETHTOOL_A_CABLE_TEST_TDR_HEADER],
+	phydev = ethnl_req_get_phydev(&req_info, tb,
+				      ETHTOOL_A_CABLE_TEST_TDR_HEADER,
 				      info->extack);
 	if (IS_ERR_OR_NULL(phydev)) {
 		ret = -EOPNOTSUPP;

net/ethtool/linkstate.c

@@ -103,7 +103,7 @@ static int linkstate_prepare_data(const struct ethnl_req_info *req_base,
 	struct phy_device *phydev;
 	int ret;
 
-	phydev = ethnl_req_get_phydev(req_base, tb[ETHTOOL_A_LINKSTATE_HEADER],
+	phydev = ethnl_req_get_phydev(req_base, tb, ETHTOOL_A_LINKSTATE_HEADER,
 				      info->extack);
 	if (IS_ERR(phydev)) {
 		ret = PTR_ERR(phydev);

net/ethtool/netlink.c

@@ -211,7 +211,7 @@ int ethnl_parse_header_dev_get(struct ethnl_req_info *req_info,
 }
 
 struct phy_device *ethnl_req_get_phydev(const struct ethnl_req_info *req_info,
-					const struct nlattr *header,
+					struct nlattr **tb, unsigned int header,
 					struct netlink_ext_ack *extack)
 {
 	struct phy_device *phydev;
@@ -225,8 +225,8 @@ struct phy_device *ethnl_req_get_phydev(const struct ethnl_req_info *req_info,
 		return req_info->dev->phydev;
 
 	phydev = phy_link_topo_get_phy(req_info->dev, req_info->phy_index);
-	if (!phydev) {
-		NL_SET_ERR_MSG_ATTR(extack, header,
+	if (!phydev && tb) {
+		NL_SET_ERR_MSG_ATTR(extack, tb[header],
 				    "no phy matching phyindex");
 		return ERR_PTR(-ENODEV);
 	}

net/ethtool/netlink.h

@@ -275,7 +275,8 @@ static inline void ethnl_parse_header_dev_put(struct ethnl_req_info *req_info)
  * ethnl_req_get_phydev() - Gets the phy_device targeted by this request,
  *			    if any. Must be called under rntl_lock().
  * @req_info:	The ethnl request to get the phy from.
- * @header:	The netlink header, used for error reporting.
+ * @tb:		The netlink attributes array, for error reporting.
+ * @header:	The netlink header index, used for error reporting.
  * @extack:	The netlink extended ACK, for error reporting.
  *
  * The caller must hold RTNL, until it's done interacting with the returned
@@ -289,7 +290,7 @@ static inline void ethnl_parse_header_dev_put(struct ethnl_req_info *req_info)
  *	   is returned.
  */
 struct phy_device *ethnl_req_get_phydev(const struct ethnl_req_info *req_info,
-					const struct nlattr *header,
+					struct nlattr **tb, unsigned int header,
 					struct netlink_ext_ack *extack);
 
 /**

net/ethtool/phy.c

@@ -125,7 +125,7 @@ static int ethnl_phy_parse_request(struct ethnl_req_info *req_base,
 	struct phy_req_info *req_info = PHY_REQINFO(req_base);
 	struct phy_device *phydev;
 
-	phydev = ethnl_req_get_phydev(req_base, tb[ETHTOOL_A_PHY_HEADER],
+	phydev = ethnl_req_get_phydev(req_base, tb, ETHTOOL_A_PHY_HEADER,
 				      extack);
 	if (!phydev)
 		return 0;

net/ethtool/plca.c

@@ -62,7 +62,7 @@ static int plca_get_cfg_prepare_data(const struct ethnl_req_info *req_base,
 	struct phy_device *phydev;
 	int ret;
 
-	phydev = ethnl_req_get_phydev(req_base, tb[ETHTOOL_A_PLCA_HEADER],
+	phydev = ethnl_req_get_phydev(req_base, tb, ETHTOOL_A_PLCA_HEADER,
 				      info->extack);
 	// check that the PHY device is available and connected
 	if (IS_ERR_OR_NULL(phydev)) {
@@ -152,7 +152,7 @@ ethnl_set_plca(struct ethnl_req_info *req_info, struct genl_info *info)
 	bool mod = false;
 	int ret;
 
-	phydev = ethnl_req_get_phydev(req_info, tb[ETHTOOL_A_PLCA_HEADER],
+	phydev = ethnl_req_get_phydev(req_info, tb, ETHTOOL_A_PLCA_HEADER,
 				      info->extack);
 	// check that the PHY device is available and connected
 	if (IS_ERR_OR_NULL(phydev))
@@ -211,7 +211,7 @@ static int plca_get_status_prepare_data(const struct ethnl_req_info *req_base,
 	struct phy_device *phydev;
 	int ret;
 
-	phydev = ethnl_req_get_phydev(req_base, tb[ETHTOOL_A_PLCA_HEADER],
+	phydev = ethnl_req_get_phydev(req_base, tb, ETHTOOL_A_PLCA_HEADER,
 				      info->extack);
 	// check that the PHY device is available and connected
 	if (IS_ERR_OR_NULL(phydev)) {

net/ethtool/pse-pd.c

@@ -64,7 +64,7 @@ static int pse_prepare_data(const struct ethnl_req_info *req_base,
 	if (ret < 0)
 		return ret;
 
-	phydev = ethnl_req_get_phydev(req_base, tb[ETHTOOL_A_PSE_HEADER],
+	phydev = ethnl_req_get_phydev(req_base, tb, ETHTOOL_A_PSE_HEADER,
 				      info->extack);
 	if (IS_ERR(phydev))
 		return -ENODEV;
@@ -261,7 +261,7 @@ ethnl_set_pse(struct ethnl_req_info *req_info, struct genl_info *info)
 	struct phy_device *phydev;
 	int ret;
 
-	phydev = ethnl_req_get_phydev(req_info, tb[ETHTOOL_A_PSE_HEADER],
+	phydev = ethnl_req_get_phydev(req_info, tb, ETHTOOL_A_PSE_HEADER,
 				      info->extack);
 	ret = ethnl_set_pse_validate(phydev, info);
 	if (ret)

net/ethtool/stats.c

@@ -138,7 +138,7 @@ static int stats_prepare_data(const struct ethnl_req_info *req_base,
 	struct phy_device *phydev;
 	int ret;
 
-	phydev = ethnl_req_get_phydev(req_base, tb[ETHTOOL_A_STATS_HEADER],
+	phydev = ethnl_req_get_phydev(req_base, tb, ETHTOOL_A_STATS_HEADER,
 				      info->extack);
 	if (IS_ERR(phydev))
 		return PTR_ERR(phydev);

net/ethtool/strset.c

@@ -309,7 +309,7 @@ static int strset_prepare_data(const struct ethnl_req_info *req_base,
 		return 0;
 	}
 
-	phydev = ethnl_req_get_phydev(req_base, tb[ETHTOOL_A_HEADER_FLAGS],
+	phydev = ethnl_req_get_phydev(req_base, tb, ETHTOOL_A_HEADER_FLAGS,
 				      info->extack);
 
 	/* phydev can be NULL, check for errors only */