[PATCH 4.19 098/134] drm/vkms: fix use-after-free when drm_gem_handle_create() fails

From: Greg Kroah-Hartman
Date: Mon Apr 01 2019 - 14:00:24 EST

4.19-stable review patch. If anyone has any objections, please let me know.


From: Eric Biggers <ebiggers@xxxxxxxxxx>

commit 36b6c9ed45afe89045973e8dee1b004dd5372d40 upstream.

If drm_gem_handle_create() fails in vkms_gem_create(), then the
vkms_gem_object is freed twice: once when the reference is dropped by
drm_gem_object_put_unlocked(), and again by the extra calls to
drm_gem_object_release() and kfree().

Fix it by skipping the second release and free.

This bug was originally found in the vgem driver by syzkaller using
fault injection, but I noticed it's also present in the vkms driver.

Fixes: 559e50fd34d1 ("drm/vkms: Add dumb operations")
Cc: Rodrigo Siqueira <rodrigosiqueiramelo@xxxxxxxxx>
Cc: Haneen Mohammed <hamohammed.sa@xxxxxxxxx>
Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Rodrigo Siqueira <rodrigosiqueiramelo@xxxxxxxxx>
Signed-off-by: Rodrigo Siqueira <rodrigosiqueiramelo@xxxxxxxxx>
Link: https://patchwork.freedesktop.org/patch/msgid/20190226220858.214438-1-ebiggers@xxxxxxxxxx
Signed-off-by: Maxime Ripard <maxime.ripard@xxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

drivers/gpu/drm/vkms/vkms_gem.c | 5 +----
1 file changed, 1 insertion(+), 4 deletions(-)

--- a/drivers/gpu/drm/vkms/vkms_gem.c
+++ b/drivers/gpu/drm/vkms/vkms_gem.c
@@ -110,11 +110,8 @@ struct drm_gem_object *vkms_gem_create(s

ret = drm_gem_handle_create(file, &obj->gem, handle);
- if (ret) {
- drm_gem_object_release(&obj->gem);
- kfree(obj);
+ if (ret)
return ERR_PTR(ret);
- }

return &obj->gem;