drm/vkms: fix use-after-free when drm_gem_handle_create() fails

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 <[email protected]>
Cc: Haneen Mohammed <[email protected]>
Cc: Daniel Vetter <[email protected]>
Cc: Chris Wilson <[email protected]>
Cc: [email protected]
Signed-off-by: Eric Biggers <[email protected]>
Reviewed-by: Chris Wilson <[email protected]>
Reviewed-by: Rodrigo Siqueira <[email protected]>
Signed-off-by: Rodrigo Siqueira <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]
Signed-off-by: Maxime Ripard <[email protected]>

diff --git a/drivers/gpu/drm/vkms/vkms_gem.c b/drivers/gpu/drm/vkms/vkms_gem.c
index 138b0bb325cf9662cd59b5a54158947dc691a2d9..69048e73377dc97855aa3b71491008e5993a5304 100644 (file)
--- a/drivers/gpu/drm/vkms/vkms_gem.c
+++ b/drivers/gpu/drm/vkms/vkms_gem.c
@@ -111,11 +111,8 @@ struct drm_gem_object *vkms_gem_create(struct drm_device *dev,
 
        ret = drm_gem_handle_create(file, &obj->gem, handle);
        drm_gem_object_put_unlocked(&obj->gem);
-       if (ret) {
-               drm_gem_object_release(&obj->gem);
-               kfree(obj);
+       if (ret)
                return ERR_PTR(ret);
-       }
 
        return &obj->gem;
 }