[PATCH AUTOSEL 4.9 04/13] spi: spidev: fix a race between spidev_release and spidev_remove

Sasha Levin
2020-07-02T01:29:33Z

From: Zhenzhong Duan <zhenzhong.duan@gmail.com>

[ Upstream commit abd42781c3d2155868821f1b947ae45bbc33330d ]

Imagine below scene, spidev is referenced after it's freed.

spidev_release() spidev_remove()
...
spin_lock_irq(&spidev->spi_lock);
spidev->spi = NULL;
spin_unlock_irq(&spidev->spi_lock);
mutex_lock(&device_list_lock);
dofree = (spidev->spi == NULL);
if (dofree)
kfree(spidev);
mutex_unlock(&device_list_lock);
mutex_lock(&device_list_lock);
list_del(&spidev->device_entry);
device_destroy(spidev_class, spidev->devt);
clear_bit(MINOR(spidev->devt), minors);
if (spidev->users == 0)
kfree(spidev);
mutex_unlock(&device_list_lock);

Fix it by resetting spidev->spi in device_list_lock's protection.

Signed-off-by: Zhenzhong Duan <zhenzhong.duan@gmail.com>
Link: https://lore.kernel.org/r/20200618032125.4650-1-zhenzhong.duan@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/spi/spidev.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/spi/spidev.c b/drivers/spi/spidev.c
index a685c6114a8d5..67ad7e46da42d 100644
--- a/drivers/spi/spidev.c
+++ b/drivers/spi/spidev.c
@@ -809,13 +809,13 @@ static int spidev_remove(struct spi_device *spi)
{
struct spidev_data *spidev = spi_get_drvdata(spi);

+ /* prevent new opens */
+ mutex_lock(&device_list_lock);
/* make sure ops on existing fds can abort cleanly */
spin_lock_irq(&spidev->spi_lock);
spidev->spi = NULL;
spin_unlock_irq(&spidev->spi_lock);

- /* prevent new opens */
- mutex_lock(&device_list_lock);
list_del(&spidev->device_entry);
device_destroy(spidev_class, spidev->devt);
clear_bit(MINOR(spidev->devt), minors);
--
2.25.1