most: usb: Fix use-after-free in hdm_disconnect

hdm_disconnect() calls most_deregister_interface(), which eventually
unregisters the MOST interface device with device_unregister(iface->dev).
If that drops the last reference, the device core may call release_mdev()
immediately while hdm_disconnect() is still executing.

The old code also freed several mdev-owned allocations in
hdm_disconnect() and then performed additional put_device() calls.
Depending on refcount order, this could lead to use-after-free or
double-free when release_mdev() ran (or when unregister paths also
performed puts).

Fix by moving the frees of mdev-owned allocations into release_mdev(),
so they happen exactly once when the device is truly released, and by
dropping the extra put_device() calls in hdm_disconnect() that are
redundant after device_unregister() and most_deregister_interface().

This addresses the KASAN slab-use-after-free reported by syzbot in
hdm_disconnect(). See report and stack traces in the bug link below.

Reported-by: [email protected]
Cc: stable <[email protected]>
Closes: https://syzkaller.appspot.com/bug?extid=916742d5d24f6c254761
Fixes: 97a6f77 ("drivers: most: add USB adapter driver")
Signed-off-by: Victoria Votokina <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: Victoria Votokina

drivers/most/most_usb.c

@@ -929,6 +929,10 @@ static void release_mdev(struct device *dev)
 {
 	struct most_dev *mdev = to_mdev_from_dev(dev);
 
+	kfree(mdev->busy_urbs);
+	kfree(mdev->cap);
+	kfree(mdev->conf);
+	kfree(mdev->ep_address);
 	kfree(mdev);
 }
 /**
@@ -1121,13 +1125,6 @@ static void hdm_disconnect(struct usb_interface *interface)
 	if (mdev->dci)
 		device_unregister(&mdev->dci->dev);
 	most_deregister_interface(&mdev->iface);
-
-	kfree(mdev->busy_urbs);
-	kfree(mdev->cap);
-	kfree(mdev->conf);
-	kfree(mdev->ep_address);
-	put_device(&mdev->dci->dev);
-	put_device(&mdev->dev);
 }
 
 static int hdm_suspend(struct usb_interface *interface, pm_message_t message)