Forwarded: [PATCH] media: em28xx: fix v4l2 use-after-free after failed init

[syzbot <syzbot+54648a6c1187a7ef46a6@syzkaller.appspotmail.com>]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org.

***

Subject: [PATCH] media: em28xx: fix v4l2 use-after-free after failed init
Author: drifabdelmalekmohamedsaid@gmail.com

#syz test
---
 drivers/media/usb/em28xx/em28xx-video.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/drivers/media/usb/em28xx/em28xx-video.c b/drivers/media/usb/em28xx/em28xx-video.c
index 84424284d486..924a3f7977c9 100644
--- a/drivers/media/usb/em28xx/em28xx-video.c
+++ b/drivers/media/usb/em28xx/em28xx-video.c
@@ -2414,7 +2414,7 @@ static int em28xx_v4l2_open(struct file *filp)
  */
 static int em28xx_v4l2_fini(struct em28xx *dev)
 {
-	struct em28xx_v4l2 *v4l2 = dev->v4l2;
+	struct em28xx_v4l2 *v4l2;
 
 	if (dev->is_audio_only) {
 		/* Shouldn't initialize IR for this interface */
@@ -2426,13 +2426,17 @@ static int em28xx_v4l2_fini(struct em28xx *dev)
 		return 0;
 	}
 
-	if (!v4l2)
-		return 0;
-
 	dev_info(&dev->intf->dev, "Closing video extension\n");
 
 	mutex_lock(&dev->lock);
 
+	/* matches em28xx_v4l2_init error paths */
+	v4l2 = dev->v4l2;
+	if (!v4l2){
+		mutex_unlock(&dev->lock);
+		return 0;
+	}
+
 	v4l2_device_disconnect(&v4l2->v4l2_dev);
 
 	em28xx_uninit_usb_xfer(dev, EM28XX_ANALOG_MODE);
@@ -3129,6 +3133,9 @@ static int em28xx_v4l2_init(struct em28xx *dev)
 		vb2_video_unregister_device(&v4l2->vdev);
 	}
 
+	/* matches check in em28xx_v4l2_fini (under the same lock) */
+	dev->v4l2 = NULL;
+
 	mutex_unlock(&dev->lock);
 
 	/*
-- 
2.43.0