spi: atmel-quadspi: Fix use-after-free on unbind

atmel_qspi_remove() accesses the driver's private data after calling
spi_unregister_controller() even though that function releases the last
reference on the spi_controller 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: 2d30ac5e ("mtd: spi-nor: atmel-quadspi: Use spi-mem interface for atmel-quadspi driver")
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Cc: <stable@vger.kernel.org> # v5.0+: 5e844cc3: spi: Introduce device-managed SPI controller allocation
Cc: <stable@vger.kernel.org> # v5.0+
Cc: Piotr Bugalski <bugalski.piotr@gmail.com>
Link: https://lore.kernel.org/r/4b05c65cf6f1ea3251484fe9a00b4c65478a1ae3.1607286887.git.lukas@wunner.deSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/atmel-quadspi.c

@@ -535,7 +535,7 @@ static int atmel_qspi_probe(struct platform_device *pdev)
 	struct resource *res;
 	int irq, err = 0;
 
-	ctrl = spi_alloc_master(&pdev->dev, sizeof(*aq));
+	ctrl = devm_spi_alloc_master(&pdev->dev, sizeof(*aq));
 	if (!ctrl)
 		return -ENOMEM;
 
@@ -557,8 +557,7 @@ static int atmel_qspi_probe(struct platform_device *pdev)
 	aq->regs = devm_ioremap_resource(&pdev->dev, res);
 	if (IS_ERR(aq->regs)) {
 		dev_err(&pdev->dev, "missing registers\n");
-		err = PTR_ERR(aq->regs);
-		goto exit;
+		return PTR_ERR(aq->regs);
 	}
 
 	/* Map the AHB memory */
@@ -566,8 +565,7 @@ static int atmel_qspi_probe(struct platform_device *pdev)
 	aq->mem = devm_ioremap_resource(&pdev->dev, res);
 	if (IS_ERR(aq->mem)) {
 		dev_err(&pdev->dev, "missing AHB memory\n");
-		err = PTR_ERR(aq->mem);
-		goto exit;
+		return PTR_ERR(aq->mem);
 	}
 
 	aq->mmap_size = resource_size(res);
@@ -579,15 +577,14 @@ static int atmel_qspi_probe(struct platform_device *pdev)
 
 	if (IS_ERR(aq->pclk)) {
 		dev_err(&pdev->dev, "missing peripheral clock\n");
-		err = PTR_ERR(aq->pclk);
-		goto exit;
+		return PTR_ERR(aq->pclk);
 	}
 
 	/* Enable the peripheral clock */
 	err = clk_prepare_enable(aq->pclk);
 	if (err) {
 		dev_err(&pdev->dev, "failed to enable the peripheral clock\n");
-		goto exit;
+		return err;
 	}
 
 	aq->caps = of_device_get_match_data(&pdev->dev);
@@ -638,8 +635,6 @@ static int atmel_qspi_probe(struct platform_device *pdev)
 	clk_disable_unprepare(aq->qspick);
 disable_pclk:
 	clk_disable_unprepare(aq->pclk);
-exit:
-	spi_controller_put(ctrl);
 
 	return err;
 }