spi: spidev: fix a race between spidev_release and spidev_remove

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>

diff --git a/drivers/spi/spidev.c b/drivers/spi/spidev.c
index d753df700e9ea3cc3373b952c996e876e9a26b24..f74ea26c382f20e52d475bb22f5dea3aaddbbf5b 100644 (file)
--- a/drivers/spi/spidev.c
+++ b/drivers/spi/spidev.c
@@ -787,13 +787,13 @@ 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);