[PATCH] spi: stm32: Fix use-after-free on unbind

stm32_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: 8d559a64f00b ("spi: stm32: drop devres version of spi_register_master")

Reported-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Alain Volmat <alain.volmat@foss.st.com>
---
 drivers/spi/spi-stm32.c | 24 ++++++++++--------------
 1 file changed, 10 insertions(+), 14 deletions(-)

diff --git a/drivers/spi/spi-stm32.c b/drivers/spi/spi-stm32.c
index 97cf3a2d4180..7f0244a246e9 100644
--- a/drivers/spi/spi-stm32.c
+++ b/drivers/spi/spi-stm32.c

@@ -1803,7 +1803,7 @@ static int stm32_spi_probe(struct platform_device *pdev)
 	struct reset_control *rst;
 	int ret;
 
-	master = spi_alloc_master(&pdev->dev, sizeof(struct stm32_spi));
+	master = devm_spi_alloc_master(&pdev->dev, sizeof(struct stm32_spi));
 	if (!master) {
 		dev_err(&pdev->dev, "spi master allocation failed\n");
 		return -ENOMEM;

@@ -1821,18 +1821,16 @@ static int stm32_spi_probe(struct platform_device *pdev)
 
 	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
 	spi->base = devm_ioremap_resource(&pdev->dev, res);
-	if (IS_ERR(spi->base)) {
-		ret = PTR_ERR(spi->base);
-		goto err_master_put;
-	}
+	if (IS_ERR(spi->base))
+		return PTR_ERR(spi->base);
 
 	spi->phys_addr = (dma_addr_t)res->start;
 
 	spi->irq = platform_get_irq(pdev, 0);
-	if (spi->irq <= 0) {
-		ret = dev_err_probe(&pdev->dev, spi->irq, "failed to get irq\n");
-		goto err_master_put;
-	}
+	if (spi->irq <= 0)
+		return dev_err_probe(&pdev->dev, spi->irq,
+				     "failed to get irq\n");
+
 	ret = devm_request_threaded_irq(&pdev->dev, spi->irq,
 					spi->cfg->irq_handler_event,
 					spi->cfg->irq_handler_thread,

@@ -1840,20 +1838,20 @@ static int stm32_spi_probe(struct platform_device *pdev)
 	if (ret) {
 		dev_err(&pdev->dev, "irq%d request failed: %d\n", spi->irq,
 			ret);
-		goto err_master_put;
+		return ret;
 	}
 
 	spi->clk = devm_clk_get(&pdev->dev, NULL);
 	if (IS_ERR(spi->clk)) {
 		ret = PTR_ERR(spi->clk);
 		dev_err(&pdev->dev, "clk get failed: %d\n", ret);
-		goto err_master_put;
+		return ret;
 	}
 
 	ret = clk_prepare_enable(spi->clk);
 	if (ret) {
 		dev_err(&pdev->dev, "clk enable failed: %d\n", ret);
-		goto err_master_put;
+		return ret;
 	}
 	spi->clk_rate = clk_get_rate(spi->clk);
 	if (!spi->clk_rate) {

@@ -1949,8 +1947,6 @@ static int stm32_spi_probe(struct platform_device *pdev)
 		dma_release_channel(spi->dma_rx);
 err_clk_disable:
 	clk_disable_unprepare(spi->clk);
-err_master_put:
-	spi_master_put(master);
 
 	return ret;
 }

-- 
2.17.1


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On Thu, 18 Mar 2021 08:24:50 +0100, Alain Volmat wrote:

stm32_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.

[...]

Applied to

   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git for-next

Thanks!

[1/1] spi: stm32: Fix use-after-free on unbind
      commit: 79c6246ae8793448c05da86a4c82298eed8549b0

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark

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