Re: [syzbot] [media?] KASAN: slab-use-after-free Read in em28xx_release_resources

[Hillf Danton <hdanton@sina.com>]

> Date: Thu, 08 Jan 2026 20:22:24 -0800
> syzbot has found a reproducer for the following issue on:
> 
> HEAD commit:    79b95d74470d Merge tag 'hid-for-linus-2026010801' of git:/..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=112b219a580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=a94030c847137a18
> dashboard link: https://syzkaller.appspot.com/bug?extid=16062f26c6480975e5ed
> compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=152b219a580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13e6e922580000

#syz test

--- x/drivers/media/usb/em28xx/em28xx-video.c
+++ y/drivers/media/usb/em28xx/em28xx-video.c
@@ -2150,6 +2150,10 @@ static int em28xx_v4l2_open(struct file
 	if (mutex_lock_interruptible(&dev->lock))
 		return -ERESTARTSYS;
 
+	if (dev->v4l2 == NULL) {
+		mutex_unlock(&dev->lock);
+		return -EINVAL;
+	}
 	ret = v4l2_fh_open(filp);
 	if (ret) {
 		dev_err(&dev->intf->dev,
@@ -2898,7 +2902,6 @@ unregister_dev:
 	v4l2_device_unregister(&v4l2->v4l2_dev);
 err:
 	dev->v4l2 = NULL;
-	kref_put(&v4l2->ref, em28xx_free_v4l2);
 	mutex_unlock(&dev->lock);
 	return ret;
 }
--