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

[Sascha Hauer <s.hauer@xxxxxxxxxxxxxx>]

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@xxxxxxxxxxxxxx>
---

This fixes the issue reported at https://marc.info/?l=linux-spi&m=160068648808293&w=2
for the fsl-dspi driver in the way Mark suggested. A whole lot of other SPI drivers
are affected by this issue and need a similar fix. Here is a fix for the driver
I currently care about.

 drivers/spi/spi-fsl-dspi.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/spi/spi-fsl-dspi.c b/drivers/spi/spi-fsl-dspi.c
index 91c6affe139c..aae9f9a7aea6 100644
--- a/drivers/spi/spi-fsl-dspi.c
+++ b/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);
-- 
2.28.0