spi: fsl-dspi: fix use-after-free in remove path

spi_unregister_controller() not only unregisters the controller, but
also frees the controller. This will free the driver data with it, so
we must not access it later dspi_remove().

Solve this by allocating the driver data separately from the SPI
controller.
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Link: https://lore.kernel.org/r/20200923131026.20707-1-s.hauer@pengutronix.deSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-fsl-dspi.c

@@ -1273,11 +1273,14 @@ static int dspi_probe(struct platform_device *pdev)
 	void __iomem *base;
 	bool big_endian;
 
-	ctlr = spi_alloc_master(&pdev->dev, sizeof(struct fsl_dspi));
+	dspi = devm_kzalloc(&pdev->dev, sizeof(*dspi), GFP_KERNEL);
+	if (!dspi)
+		return -ENOMEM;
+
+	ctlr = spi_alloc_master(&pdev->dev, 0);
 	if (!ctlr)
 		return -ENOMEM;
 
-	dspi = spi_controller_get_devdata(ctlr);
 	dspi->pdev = pdev;
 	dspi->ctlr = ctlr;
 
@@ -1414,7 +1417,7 @@ static int dspi_probe(struct platform_device *pdev)
 	if (dspi->devtype_data->trans_mode != DSPI_DMA_MODE)
 		ctlr->ptp_sts_supported = true;
 
-	platform_set_drvdata(pdev, ctlr);
+	platform_set_drvdata(pdev, dspi);
 
 	ret = spi_register_controller(ctlr);
 	if (ret != 0) {
@@ -1437,8 +1440,7 @@ static int dspi_probe(struct platform_device *pdev)
 
 static int dspi_remove(struct platform_device *pdev)
 {
-	struct spi_controller *ctlr = platform_get_drvdata(pdev);
-	struct fsl_dspi *dspi = spi_controller_get_devdata(ctlr);
+	struct fsl_dspi *dspi = platform_get_drvdata(pdev);
 
 	/* Disconnect from the SPI framework */
 	spi_unregister_controller(dspi->ctlr);