[PATCH 5.7 018/166] spi: spidev: fix a race between spidev_release and spidev_remove

[Greg Kroah-Hartman]

From: Zhenzhong Duan <zhenzhong.d...@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.d...@gmail.com>
Link: https://lore.kernel.org/r/20200618032125.4650-1-zhenzhong.d...@gmail.com
Signed-off-by: Mark Brown <broo...@kernel.org>
Signed-off-by: Sasha Levin <sas...@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 80dd1025b9530..82e6481fdf950 100644
--- a/drivers/spi/spidev.c
+++ b/drivers/spi/spidev.c
@@ -786,13 +786,13 @@ 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