[PATCH 6.12.y] hsr: hold rcu and dev lock for hsr_get_port_ndev

[Sasha Levin <sashal@kernel.org>]

From: Hangbin Liu <liuhangbin@gmail.com>

[ Upstream commit 847748fc66d08a89135a74e29362a66ba4e3ab15 ]

hsr_get_port_ndev calls hsr_for_each_port, which need to hold rcu lock.
On the other hand, before return the port device, we need to hold the
device reference to avoid UaF in the caller function.

Suggested-by: Paolo Abeni <pabeni@redhat.com>
Fixes: 9c10dd8eed74 ("net: hsr: Create and export hsr_get_port_ndev()")
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20250905091533.377443-4-liuhangbin@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
[ Drop multicast filtering changes ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/hsr/hsr_device.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/net/hsr/hsr_device.c b/net/hsr/hsr_device.c
index 386aba50930a3..acbd77ce6afce 100644
--- a/net/hsr/hsr_device.c
+++ b/net/hsr/hsr_device.c
@@ -682,9 +682,14 @@ struct net_device *hsr_get_port_ndev(struct net_device *ndev,
 	struct hsr_priv *hsr = netdev_priv(ndev);
 	struct hsr_port *port;
 
+	rcu_read_lock();
 	hsr_for_each_port(hsr, port)
-		if (port->type == pt)
+		if (port->type == pt) {
+			dev_hold(port->dev);
+			rcu_read_unlock();
 			return port->dev;
+		}
+	rcu_read_unlock();
 	return NULL;
 }
 EXPORT_SYMBOL(hsr_get_port_ndev);
-- 
2.51.0