linux-kernel - [PATCH] spi: fix use-after-free of the add

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Date:   Thu, 11 Nov 2021 09:37:13 +0100
From:   Michael Walle <michael@...le.cc>
To:     linux-spi@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Mark Brown <broonie@...nel.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Michael Walle <michael@...le.cc>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>, Lukas Wunner <lukas@...ner.de>,
        stable@...r.kernel.org
Subject: [PATCH] spi: fix use-after-free of the add_lock mutex

Commit 6098475d4cb4 ("spi: Fix deadlock when adding SPI controllers on
SPI buses") introduced a per-controller mutex. But mutex_unlock() of
said lock is called after the controller is already freed:

  spi_unregister_controller(ctlr)
  -> put_device(&ctlr->dev)
    -> spi_controller_release(dev)
  -> mutex_unlock(&ctrl->add_lock)

Move the put_device() after the mutex_unlock().

Fixes: 6098475d4cb4 ("spi: Fix deadlock when adding SPI controllers on SPI buses")
Signed-off-by: Michael Walle <michael@...le.cc>
Reviewed-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
Reviewed-by: Lukas Wunner <lukas@...ner.de>
Cc: stable@...r.kernel.org # v5.15
---
changes since RFC:
 - fix call graph indendation in commit message

 drivers/spi/spi.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index b23e675953e1..fdd530b150a7 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -3099,12 +3099,6 @@ void spi_unregister_controller(struct spi_controller *ctlr)
 
 	device_del(&ctlr->dev);
 
-	/* Release the last reference on the controller if its driver
-	 * has not yet been converted to devm_spi_alloc_master/slave().
-	 */
-	if (!ctlr->devm_allocated)
-		put_device(&ctlr->dev);
-
 	/* free bus id */
 	mutex_lock(&board_lock);
 	if (found == ctlr)
@@ -3113,6 +3107,12 @@ void spi_unregister_controller(struct spi_controller *ctlr)
 
 	if (IS_ENABLED(CONFIG_SPI_DYNAMIC))
 		mutex_unlock(&ctlr->add_lock);
+
+	/* Release the last reference on the controller if its driver
+	 * has not yet been converted to devm_spi_alloc_master/slave().
+	 */
+	if (!ctlr->devm_allocated)
+		put_device(&ctlr->dev);
 }
 EXPORT_SYMBOL_GPL(spi_unregister_controller);
 
-- 
2.30.2