linux-kernel - [PATCH 1/2] spi: spidev: fix a race between spidev_release and spidev

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Date:   Thu, 18 Jun 2020 11:21:24 +0800
From:   Zhenzhong Duan <zhenzhong.duan@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     linux-spi@...r.kernel.org, broonie@...nel.org,
        Zhenzhong Duan <zhenzhong.duan@...il.com>
Subject: [PATCH 1/2] 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@...il.com>
---
 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 d753df7..f74ea26 100644
--- 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);
-- 
1.8.3.1