[PATCH AUTOSEL 4.4 4/7] spi: spidev: fix a potential use-after-free in spidev_release()

Sasha Levin
2020-07-02T01:28:44Z

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

[ Upstream commit 06096cc6c5a84ced929634b0d79376b94c65a4bd ]

If an spi device is unbounded from the driver before the release
process, there will be an NULL pointer reference when it's
referenced in spi_slave_abort().

Fix it by checking it's already freed before reference.

Signed-off-by: Zhenzhong Duan <zhenzhong.duan@gmail.com>
Link: https://lore.kernel.org/r/20200618032125.4650-2-zhenzhong.duan@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/spi/spidev.c | 20 ++++++++++----------
1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/drivers/spi/spidev.c b/drivers/spi/spidev.c
index 80beb8406f200..7969f5484aee8 100644
--- a/drivers/spi/spidev.c
+++ b/drivers/spi/spidev.c
@@ -635,15 +635,20 @@ static int spidev_open(struct inode *inode, struct file *filp)
static int spidev_release(struct inode *inode, struct file *filp)
{
struct spidev_data *spidev;
+ int dofree;

mutex_lock(&device_list_lock);
spidev = filp->private_data;
filp->private_data = NULL;

+ spin_lock_irq(&spidev->spi_lock);
+ /* ... after we unbound from the underlying device? */
+ dofree = (spidev->spi == NULL);
+ spin_unlock_irq(&spidev->spi_lock);
+
/* last close? */
spidev->users--;
if (!spidev->users) {
- int dofree;

kfree(spidev->tx_buffer);
spidev->tx_buffer = NULL;
@@ -651,19 +656,14 @@ static int spidev_release(struct inode *inode, struct file *filp)
kfree(spidev->rx_buffer);
spidev->rx_buffer = NULL;

- spin_lock_irq(&spidev->spi_lock);
- if (spidev->spi)
- spidev->speed_hz = spidev->spi->max_speed_hz;
-
- /* ... after we unbound from the underlying device? */
- dofree = (spidev->spi == NULL);
- spin_unlock_irq(&spidev->spi_lock);
-
if (dofree)
kfree(spidev);
+ else
+ spidev->speed_hz = spidev->spi->max_speed_hz;
}
#ifdef CONFIG_SPI_SLAVE
- spi_slave_abort(spidev->spi);
+ if (!dofree)
+ spi_slave_abort(spidev->spi);
#endif
mutex_unlock(&device_list_lock);

--
2.25.1