bus: fsl-mc-bus: fix KASAN use-after-free in fsl_mc_bus_remove()

In fsl_mc_bus_remove(), mc->root_mc_bus_dev->mc_io is passed to
fsl_destroy_mc_io(). However, mc->root_mc_bus_dev is already freed in
fsl_mc_device_remove(). Then reference to mc->root_mc_bus_dev->mc_io
triggers KASAN use-after-free. To avoid the use-after-free, keep the
reference to mc->root_mc_bus_dev->mc_io in a local variable and pass to
fsl_destroy_mc_io().

This patch needs rework to apply to kernels older than v5.15.

Fixes: f9362714 ("staging: fsl-mc: fix asymmetry in destroy of mc_io")
Cc: stable@vger.kernel.org # v5.15+
Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Link: https://lore.kernel.org/r/20220601105159.87752-1-shinichiro.kawasaki@wdc.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/bus/fsl-mc/fsl-mc-bus.c

@@ -1239,14 +1239,14 @@ static int fsl_mc_bus_probe(struct platform_device *pdev)
 static int fsl_mc_bus_remove(struct platform_device *pdev)
 {
 	struct fsl_mc *mc = platform_get_drvdata(pdev);
+	struct fsl_mc_io *mc_io;
 
 	if (!fsl_mc_is_root_dprc(&mc->root_mc_bus_dev->dev))
 		return -EINVAL;
 
+	mc_io = mc->root_mc_bus_dev->mc_io;
 	fsl_mc_device_remove(mc->root_mc_bus_dev);
-
-	fsl_destroy_mc_io(mc->root_mc_bus_dev->mc_io);
-	mc->root_mc_bus_dev->mc_io = NULL;
+	fsl_destroy_mc_io(mc_io);
 
 	bus_unregister_notifier(&fsl_mc_bus_type, &fsl_mc_nb);