Re: [syzbot] [dri?] KASAN: slab-use-after-free Read in drm_gem_object_release_handle

[Hillf Danton <hdanton@sina.com>]

> Date: Mon, 13 Apr 2026 10:16:36 -0700	[thread overview]
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    f5459048c38a Merge tag 'i2c-for-7.0-final' of git://git.ke..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=1028d106580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=6754c86e8d9e4c91
> dashboard link: https://syzkaller.appspot.com/bug?extid=b2e951687503f32f74ce
> compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1428d106580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17509036580000

#syz test

--- x/drivers/gpu/drm/drm_gem.c
+++ y/drivers/gpu/drm/drm_gem.c
@@ -401,22 +401,20 @@ drm_gem_handle_delete(struct drm_file *f
 {
 	struct drm_gem_object *obj;
 
+	mutex_lock(&filp->prime.lock);
 	spin_lock(&filp->table_lock);
 
 	/* Check if we currently have a reference on the object */
-	obj = idr_replace(&filp->object_idr, NULL, handle);
+	obj = idr_find(&filp->object_idr, handle);
+	idr_remove(&filp->object_idr, handle);
 	spin_unlock(&filp->table_lock);
+	mutex_unlock(&filp->prime.lock);
+
 	if (IS_ERR_OR_NULL(obj))
 		return -EINVAL;
-
 	/* Release driver's reference and decrement refcount. */
 	drm_gem_object_release_handle(handle, obj, filp);
 
-	/* And finally make the handle available for future allocations. */
-	spin_lock(&filp->table_lock);
-	idr_remove(&filp->object_idr, handle);
-	spin_unlock(&filp->table_lock);
-
 	return 0;
 }
 EXPORT_SYMBOL(drm_gem_handle_delete);
@@ -1012,17 +1010,20 @@ int drm_gem_change_handle_ioctl(struct d
 		return -EINVAL;
 	handle = args->new_handle;
 
+	mutex_lock(&file_priv->prime.lock);
+
 	obj = drm_gem_object_lookup(file_priv, args->handle);
-	if (!obj)
+	if (!obj) {
+		mutex_unlock(&file_priv->prime.lock);
 		return -ENOENT;
+	}
 
 	if (args->handle == handle) {
+		mutex_unlock(&file_priv->prime.lock);
 		ret = 0;
 		goto out;
 	}
 
-	mutex_lock(&file_priv->prime.lock);
-
 	spin_lock(&file_priv->table_lock);
 	ret = idr_alloc(&file_priv->object_idr, obj, handle, handle + 1,
 			GFP_NOWAIT);
@@ -1085,8 +1086,22 @@ drm_gem_open(struct drm_device *dev, str
 void
 drm_gem_release(struct drm_device *dev, struct drm_file *file_private)
 {
-	idr_for_each(&file_private->object_idr,
-		     &drm_gem_object_release_handle, file_private);
+	struct drm_gem_object *obj;
+	int id;
+
+	for (;;) {
+		id = 0;
+		mutex_lock(&file_private->prime.lock);
+		spin_lock(&file_private->table_lock);
+		obj = idr_get_next(&file_private->object_idr, &id);
+		if (obj)
+			idr_remove(&file_private->object_idr, id);
+		spin_unlock(&file_private->table_lock);
+		mutex_unlock(&file_private->prime.lock);
+		if (!obj)
+			break;
+		drm_gem_object_release_handle(id, obj, file_private);
+	}
 	idr_destroy(&file_private->object_idr);
 }
 
--