linux-kernel - [PATCH AUTOSEL 4.4 4/7] spi: spidev: fix a potential use-after-free in spidev

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Message-Id: <20200702012729.2702141-4-sashal@kernel.org>
Date:   Wed,  1 Jul 2020 21:27:26 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Zhenzhong Duan <zhenzhong.duan@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Sasha Levin <sashal@...nel.org>, linux-spi@...r.kernel.org
Subject: [PATCH AUTOSEL 4.4 4/7] spi: spidev: fix a potential use-after-free in spidev_release()

From: Zhenzhong Duan <zhenzhong.duan@...il.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@...il.com>
Link: https://lore.kernel.org/r/20200618032125.4650-2-zhenzhong.duan@gmail.com
Signed-off-by: Mark Brown <broonie@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.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