spi: bcm2835aux: Fix use-after-free on unbind

bcm2835aux_spi_remove() accesses the driver's private data after calling
spi_unregister_master() even though that function releases the last
reference on the spi_master and thereby frees the private data.

Fix by switching over to the new devm_spi_alloc_master() helper which
keeps the private data accessible until the driver has unbound.

Fixes: b9dd3f6d ("spi: bcm2835aux: Fix controller unregister order")
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Cc: <stable@vger.kernel.org> # v4.4+: 123456789abc: spi: Introduce device-managed SPI controller allocation
Cc: <stable@vger.kernel.org> # v4.4+: b9dd3f6d: spi: bcm2835aux: Fix controller unregister order
Cc: <stable@vger.kernel.org> # v4.4+
Link: https://lore.kernel.org/r/b290b06357d0c0bdee9cecc539b840a90630f101.1605121038.git.lukas@wunner.deSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-bcm2835aux.c

@@ -494,7 +494,7 @@ static int bcm2835aux_spi_probe(struct platform_device *pdev)
 	unsigned long clk_hz;
 	int err;
 
-	master = spi_alloc_master(&pdev->dev, sizeof(*bs));
+	master = devm_spi_alloc_master(&pdev->dev, sizeof(*bs));
 	if (!master)
 		return -ENOMEM;
 
@@ -524,29 +524,24 @@ static int bcm2835aux_spi_probe(struct platform_device *pdev)
 
 	/* the main area */
 	bs->regs = devm_platform_ioremap_resource(pdev, 0);
-	if (IS_ERR(bs->regs)) {
-		err = PTR_ERR(bs->regs);
-		goto out_master_put;
-	}
+	if (IS_ERR(bs->regs))
+		return PTR_ERR(bs->regs);
 
 	bs->clk = devm_clk_get(&pdev->dev, NULL);
 	if (IS_ERR(bs->clk)) {
-		err = PTR_ERR(bs->clk);
 		dev_err(&pdev->dev, "could not get clk: %d\n", err);
-		goto out_master_put;
+		return PTR_ERR(bs->clk);
 	}
 
 	bs->irq = platform_get_irq(pdev, 0);
-	if (bs->irq <= 0) {
-		err = bs->irq ? bs->irq : -ENODEV;
-		goto out_master_put;
-	}
+	if (bs->irq <= 0)
+		return bs->irq ? bs->irq : -ENODEV;
 
 	/* this also enables the HW block */
 	err = clk_prepare_enable(bs->clk);
 	if (err) {
 		dev_err(&pdev->dev, "could not prepare clock: %d\n", err);
-		goto out_master_put;
+		return err;
 	}
 
 	/* just checking if the clock returns a sane value */
@@ -581,8 +576,6 @@ static int bcm2835aux_spi_probe(struct platform_device *pdev)
 
 out_clk_disable:
 	clk_disable_unprepare(bs->clk);
-out_master_put:
-	spi_master_put(master);
 	return err;
 }