From: Lv Yunlong lyl2019@mail.ustc.edu.cn

[ Upstream commit 52762efa2b256ed1c5274e5177cbd52ee11a2f6a ]

In function displback_changed, has the call chain displback_connect(front_info)->xen_drm_drv_init(front_info). We can see that drm_info is assigned to front_info->drm_info and drm_info is freed in fail branch in xen_drm_drv_init().

Later displback_disconnect(front_info) is called and it calls xen_drm_drv_fini(front_info) cause a use after free by drm_info = front_info->drm_info statement.

My patch has done two things. First fixes the fail label which drm_info = kzalloc() failed and still free the drm_info. Second sets front_info->drm_info to NULL to avoid uaf.

Signed-off-by: Lv Yunlong lyl2019@mail.ustc.edu.cn Reviewed-by: Oleksandr Andrushchenko oleksandr_andrushchenko@epam.com Signed-off-by: Oleksandr Andrushchenko oleksandr_andrushchenko@epam.com Link: https://patchwork.freedesktop.org/patch/msgid/20210323014656.10068-1-lyl2019... Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/gpu/drm/xen/xen_drm_front.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/xen/xen_drm_front.c b/drivers/gpu/drm/xen/xen_drm_front.c index 30d9adf31c84..9f14d99c763c 100644 --- a/drivers/gpu/drm/xen/xen_drm_front.c +++ b/drivers/gpu/drm/xen/xen_drm_front.c @@ -521,7 +521,7 @@ static int xen_drm_drv_init(struct xen_drm_front_info *front_info) drm_dev = drm_dev_alloc(&xen_drm_driver, dev); if (IS_ERR(drm_dev)) { ret = PTR_ERR(drm_dev); - goto fail; + goto fail_dev; }

drm_info->drm_dev = drm_dev; @@ -551,8 +551,10 @@ static int xen_drm_drv_init(struct xen_drm_front_info *front_info) drm_kms_helper_poll_fini(drm_dev); drm_mode_config_cleanup(drm_dev); drm_dev_put(drm_dev); -fail: +fail_dev: kfree(drm_info); + front_info->drm_info = NULL; +fail: return ret; }