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From:   Jia-Ju Bai <baijiaju1990@gmail.com>
To:     crope@iki.fi, mchehab@kernel.org
Cc:     linux-media@vger.kernel.org, linux-kernel@vger.kernel.org,
        Jia-Ju Bai <baijiaju1990@gmail.com>
Subject: [PATCH] media: usb: msi2500: Fix a possible null-pointer dereference in msi2500_stop_streaming()
Date:   Mon, 29 Jul 2019 18:14:44 +0800
Message-Id: <20190729101444.2191-1-baijiaju1990@gmail.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

In msi2500_stop_streaming(), there is an if statement on line 870 to
check whether dev->udev is NULL:
    if (dev->udev)

When dev->udev is NULL, it is used on line 877:
    msi2500_ctrl_msg(dev, CMD_STOP_STREAMING, 0)
        usb_control_msg(dev->udev, usb_sndctrlpipe(dev->udev, 0), ...)

Thus, a possible null-pointer dereference may occur.

To fix this bug, dev->udev is checked before calling msi2500_ctrl_msg().

This bug is found by a static analysis tool STCheck written by us.

Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
---
 drivers/media/usb/msi2500/msi2500.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/media/usb/msi2500/msi2500.c b/drivers/media/usb/msi2500/msi2500.c
index 4c9b2a12acfb..a6ecd9bd35f9 100644
--- a/drivers/media/usb/msi2500/msi2500.c
+++ b/drivers/media/usb/msi2500/msi2500.c
@@ -874,7 +874,7 @@ static void msi2500_stop_streaming(struct vb2_queue *vq)
 
 	/* according to tests, at least 700us delay is required  */
 	msleep(20);
-	if (!msi2500_ctrl_msg(dev, CMD_STOP_STREAMING, 0)) {
+	if (dev->udev && !msi2500_ctrl_msg(dev, CMD_STOP_STREAMING, 0)) {
 		/* sleep USB IF / ADC */
 		msi2500_ctrl_msg(dev, CMD_WREG, 0x01000003);
 	}
-- 
2.17.0