[PATCH] drm: Fix possible UAF in drm_addmap_core

[Yi Yang]

smatch report warning as follows:

drivers/gpu/drm/drm_bufs.c:365 drm_addmap_core() warn:
 '&list->head' not removed from list

If drm_map_handle() fails in drm_addmap_core(), the list will be
freed, but the list->head will not be removed from dev->maplist,
then list traversal may cause UAF.

Fix by removeing it from list->head before free().

Fixes: 9a298b2acd77 ("drm: Remove memory debugging infrastructure.")
Signed-off-by: Yi Yang <yiyang13 at huawei.com>
---
 drivers/gpu/drm/drm_bufs.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/gpu/drm/drm_bufs.c b/drivers/gpu/drm/drm_bufs.c
index fcca21e8efac..e739e577902c 100644
--- a/drivers/gpu/drm/drm_bufs.c
+++ b/drivers/gpu/drm/drm_bufs.c
@@ -362,6 +362,7 @@ static int drm_addmap_core(struct drm_device *dev, resource_size_t offset,
 		if (map->type == _DRM_REGISTERS)
 			iounmap(map->handle);
 		kfree(map);
+		list_del(&list->head);
 		kfree(list);
 		mutex_unlock(&dev->struct_mutex);
 		return ret;
-- 
2.17.1