drm/xe/queue: move xa_alloc to prevent UAF

Evil user can guess the next id of the queue before the ioctl completes
and then call queue destroy ioctl to trigger UAF since create ioctl is
still referencing the same queue. Move the xa_alloc all the way to the end
to prevent this.

v2:
 - Rebase

Fixes: 2149ded ("drm/xe: Fix use after free when client stats are captured")
Signed-off-by: Matthew Auld <[email protected]>
Cc: Matthew Brost <[email protected]>
Reviewed-by: Nirmoy Das <[email protected]>
Reviewed-by: Matthew Brost <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]
(cherry picked from commit 1653658)
Signed-off-by: Lucas De Marchi <[email protected]>

Author: matt-auld

drivers/gpu/drm/xe/xe_exec_queue.c

@@ -635,12 +635,14 @@ int xe_exec_queue_create_ioctl(struct drm_device *dev, void *data,
 		}
 	}
 
+	q->xef = xe_file_get(xef);
+
+	/* user id alloc must always be last in ioctl to prevent UAF */
 	err = xa_alloc(&xef->exec_queue.xa, &id, q, xa_limit_32b, GFP_KERNEL);
 	if (err)
 		goto kill_exec_queue;
 
 	args->exec_queue_id = id;
-	q->xef = xe_file_get(xef);
 
 	return 0;