linux-kernel - [PATCH net-next] net: ethtool: Fix suspicious rcu

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Message-Id: <20241217140323.782346-1-kory.maincent@bootlin.com>
Date: Tue, 17 Dec 2024 15:03:23 +0100
From: Kory Maincent <kory.maincent@...tlin.com>
To: "David S. Miller" <davem@...emloft.net>,
	Kory Maincent <kory.maincent@...tlin.com>,
	netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: syzbot+a344326c05c98ba19682@...kaller.appspotmail.com,
	thomas.petazzoni@...tlin.com,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>
Subject: [PATCH net-next] net: ethtool: Fix suspicious rcu_dereference usage

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@...kaller.appspotmail.com
Closes: https://lore.kernel.org/netdev/676147f8.050a0220.37aaf.0154.GAE@google.com/
Fixes: b9e3f7dc9ed9 ("net: ethtool: tsinfo: Enhance tsinfo to support several hwtstamp by net topology")
Signed-off-by: Kory Maincent <kory.maincent@...tlin.com>
---
 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