[PATCH 5.15 229/279] spi: fix use-after-free of the add_lock mutex

Greg Kroah-Hartman
2021-11-24T14:06:50Z

From: Michael Walle <michael@walle.cc>

commit 6c53b45c71b4920b5e62f0ea8079a1da382b9434 upstream.

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@walle.cc>
Reviewed-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Lukas Wunner <lukas@wunner.de>
Cc: stable@vger.kernel.org # v5.15
Link: https://lore.kernel.org/r/20211111083713.3335171-1-michael@walle.cc
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/spi/spi.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)

--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -3020,12 +3020,6 @@ void spi_unregister_controller(struct sp

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)
@@ -3034,6 +3028,12 @@ void spi_unregister_controller(struct sp

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);