uio: Fix use-after-free in uio_open

jira VULN-497
cve CVE-2023-52439
commit-author Guanghui Feng <[email protected]>
commit 0c9ae0b

core-1				core-2
-------------------------------------------------------
uio_unregister_device		uio_open
				idev = idr_find()
device_unregister(&idev->dev)
put_device(&idev->dev)
uio_device_release
				get_device(&idev->dev)
kfree(idev)
uio_free_minor(minor)
				uio_release
				put_device(&idev->dev)
				kfree(idev)
-------------------------------------------------------

In the core-1 uio_unregister_device(), the device_unregister will kfree
idev when the idev->dev kobject ref is 1. But after core-1
device_unregister, put_device and before doing kfree, the core-2 may
get_device. Then:
1. After core-1 kfree idev, the core-2 will do use-after-free for idev.
2. When core-2 do uio_release and put_device, the idev will be double
   freed.

To address this issue, we can get idev atomic & inc idev reference with
minor_lock.

Fixes: 57c5f4d ("uio: fix crash after the device is unregistered")
	Cc: stable <[email protected]>
	Signed-off-by: Guanghui Feng <[email protected]>
	Reviewed-by: Baolin Wang <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
	Signed-off-by: Greg Kroah-Hartman <[email protected]>
(cherry picked from commit 0c9ae0b)
	Signed-off-by: Pratham Patel <[email protected]>

Author: thefossguy-ciq

drivers/uio/uio.c

@@ -464,13 +464,13 @@ static int uio_open(struct inode *inode, struct file *filep)
 
 	mutex_lock(&minor_lock);
 	idev = idr_find(&uio_idr, iminor(inode));
-	mutex_unlock(&minor_lock);
 	if (!idev) {
 		ret = -ENODEV;
+		mutex_unlock(&minor_lock);
 		goto out;
 	}
-
 	get_device(&idev->dev);
+	mutex_unlock(&minor_lock);
 
 	if (!try_module_get(idev->owner)) {
 		ret = -ENODEV;
@@ -1024,9 +1024,8 @@ void uio_unregister_device(struct uio_info *info)
 	wake_up_interruptible(&idev->wait);
 	kill_fasync(&idev->async_queue, SIGIO, POLL_HUP);
 
-	device_unregister(&idev->dev);
-
 	uio_free_minor(minor);
+	device_unregister(&idev->dev);
 
 	return;
 }