mlxsw: core: Use devm_kzalloc to allocate mlxsw_hwmon structure

KASan reported use-after-free for the hwmon structure. So fix this by
using devm_kzalloc and let the core take care about freeing the memory
during device dettach.

Reported-by: Ido Schimmel <idosch@mellanox.com>
Fixes: 89309da39 ("mlxsw: core: Implement temperature hwmon interface")
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/mellanox/mlxsw/core.c

@@ -855,7 +855,6 @@ int mlxsw_core_bus_device_register(const struct mlxsw_bus_info *mlxsw_bus_info,
 err_debugfs_init:
 	mlxsw_core->driver->fini(mlxsw_core->driver_priv);
 err_driver_init:
-	mlxsw_hwmon_fini(mlxsw_core->hwmon);
 err_hwmon_init:
 	mlxsw_emad_fini(mlxsw_core);
 err_emad_init:
@@ -878,7 +877,6 @@ void mlxsw_core_bus_device_unregister(struct mlxsw_core *mlxsw_core)
 
 	mlxsw_core_debugfs_fini(mlxsw_core);
 	mlxsw_core->driver->fini(mlxsw_core->driver_priv);
-	mlxsw_hwmon_fini(mlxsw_core->hwmon);
 	mlxsw_emad_fini(mlxsw_core);
 	mlxsw_core->bus->fini(mlxsw_core->bus_priv);
 	kfree(mlxsw_core->lag.mapping);

drivers/net/ethernet/mellanox/mlxsw/core.h

@@ -239,10 +239,6 @@ static inline int mlxsw_hwmon_init(struct mlxsw_core *mlxsw_core,
 	return 0;
 }
 
-static inline void mlxsw_hwmon_fini(struct mlxsw_hwmon *mlxsw_hwmon)
-{
-}
-
 #endif
 
 #endif

drivers/net/ethernet/mellanox/mlxsw/core_hwmon.c

@@ -334,7 +334,8 @@ int mlxsw_hwmon_init(struct mlxsw_core *mlxsw_core,
 	struct device *hwmon_dev;
 	int err;
 
-	mlxsw_hwmon = kzalloc(sizeof(*mlxsw_hwmon), GFP_KERNEL);
+	mlxsw_hwmon = devm_kzalloc(mlxsw_bus_info->dev, sizeof(*mlxsw_hwmon),
+				   GFP_KERNEL);
 	if (!mlxsw_hwmon)
 		return -ENOMEM;
 	mlxsw_hwmon->core = mlxsw_core;
@@ -367,11 +368,5 @@ int mlxsw_hwmon_init(struct mlxsw_core *mlxsw_core,
 err_hwmon_register:
 err_fans_init:
 err_temp_init:
-	kfree(mlxsw_hwmon);
 	return err;
 }
-
-void mlxsw_hwmon_fini(struct mlxsw_hwmon *mlxsw_hwmon)
-{
-	kfree(mlxsw_hwmon);
-}