[PATCH net-next] net: ethtool: Fix suspicious rcu_dereference usage

[Kory Maincent]

The __ethtool_get_ts_info function can be called with or without the
rtnl lock held. When the rtnl lock is not held, using rtnl_dereference()
triggers a warning due to improper lock context.

Replace rtnl_dereference() with rcu_dereference_rtnl() to safely
dereference the RCU pointer in both scenarios, ensuring proper handling
regardless of the rtnl lock state.

Reported-by: syzbot+a344326c05c98ba19682@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://lore.kernel.org/netdev/676147f8.050a0220.37aaf.0154.GAE@xxxxxxxxxx/
Fixes: b9e3f7dc9ed9 ("net: ethtool: tsinfo: Enhance tsinfo to support several hwtstamp by net topology")
Signed-off-by: Kory Maincent <kory.maincent@xxxxxxxxxxx>
---
 net/ethtool/common.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ethtool/common.c b/net/ethtool/common.c
index 02f941f667dd..ec6f2e2caaf9 100644
--- a/net/ethtool/common.c
+++ b/net/ethtool/common.c
@@ -870,7 +870,7 @@ int __ethtool_get_ts_info(struct net_device *dev,
 {
 	struct hwtstamp_provider *hwprov;
 
-	hwprov = rtnl_dereference(dev->hwprov);
+	hwprov = rcu_dereference_rtnl(dev->hwprov);
 	/* No provider specified, use default behavior */
 	if (!hwprov) {
 		const struct ethtool_ops *ops = dev->ethtool_ops;
-- 
2.34.1