drm: Do not allow userspace to trigger kernel warnings in drm_gem_change_handle_ioctl()

Since GEM bo handles are u32 in the uapi and the internal implementation
uses idr_alloc() which uses int ranges, passing a new handle larger than
INT_MAX trivially triggers a kernel warning:

idr_alloc():
...
	if (WARN_ON_ONCE(start < 0))
		return -EINVAL;
...

Fix it by rejecting new handles above INT_MAX and at the same time make
the end limit calculation more obvious by moving into int domain.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>
Reported-by: Zhi Wang <wangzhi@stu.xidian.edu.cn>
Fixes: 5309672 ("drm: Add DRM prime interface to reassign GEM handle")
Cc: David Francis <David.Francis@amd.com>
Cc: Felix Kuehling <felix.kuehling@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: <stable@vger.kernel.org> # v6.18+
Tested-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Tvrtko Ursulin <tursulin@ursulin.net>
Link: https://lore.kernel.org/r/20260123141540.76540-1-tvrtko.ursulin@igalia.com

Author: Tvrtko Ursulin

drivers/gpu/drm/drm_gem.c

@@ -960,35 +960,41 @@ int drm_gem_change_handle_ioctl(struct drm_device *dev, void *data,
 {
 	struct drm_gem_change_handle *args = data;
 	struct drm_gem_object *obj;
-	int ret;
+	int handle, ret;
 
 	if (!drm_core_check_feature(dev, DRIVER_GEM))
 		return -EOPNOTSUPP;
 
+	/* idr_alloc() limitation. */
+	if (args->new_handle > INT_MAX)
+		return -EINVAL;
+	handle = args->new_handle;
+
 	obj = drm_gem_object_lookup(file_priv, args->handle);
 	if (!obj)
 		return -ENOENT;
 
-	if (args->handle == args->new_handle) {
+	if (args->handle == handle) {
 		ret = 0;
 		goto out;
 	}
 
 	mutex_lock(&file_priv->prime.lock);
 
 	spin_lock(&file_priv->table_lock);
-	ret = idr_alloc(&file_priv->object_idr, obj,
-		args->new_handle, args->new_handle + 1, GFP_NOWAIT);
+	ret = idr_alloc(&file_priv->object_idr, obj, handle, handle + 1,
+			GFP_NOWAIT);
 	spin_unlock(&file_priv->table_lock);
 
 	if (ret < 0)
 		goto out_unlock;
 
 	if (obj->dma_buf) {
-		ret = drm_prime_add_buf_handle(&file_priv->prime, obj->dma_buf, args->new_handle);
+		ret = drm_prime_add_buf_handle(&file_priv->prime, obj->dma_buf,
+					       handle);
 		if (ret < 0) {
 			spin_lock(&file_priv->table_lock);
-			idr_remove(&file_priv->object_idr, args->new_handle);
+			idr_remove(&file_priv->object_idr, handle);
 			spin_unlock(&file_priv->table_lock);
 			goto out_unlock;
 		}