[PATCH 4.15 094/163] drm: Check for lessee in DROP_MASTER ioctl

[Greg Kroah-Hartman]

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

------------------

From: Keith Packard <keithp@xxxxxxxxxx>

commit 761e05a702f5d537ffcca1ba933f9f0a968aa022 upstream.

Don't let a lessee control what the current DRM master is set to;
that's the job of the "real" master. Otherwise, the lessee would
disable all access to master operations for the owner and all lessees
under it.

This matches the same check made in the SET_MASTER ioctl.

Signed-off-by: Keith Packard <keithp@xxxxxxxxxx>
Fixes: 2ed077e467ee ("drm: Add drm_object lease infrastructure [v5]")
Cc: <stable@xxxxxxxxxxxxxxx> # v4.15+
Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
Link: https://patchwork.freedesktop.org/patch/msgid/20180119015159.1606-1-keithp@xxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/gpu/drm/drm_auth.c |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/drivers/gpu/drm/drm_auth.c
+++ b/drivers/gpu/drm/drm_auth.c
@@ -230,6 +230,12 @@ int drm_dropmaster_ioctl(struct drm_devi
 	if (!dev->master)
 		goto out_unlock;
 
+	if (file_priv->master->lessor != NULL) {
+		DRM_DEBUG_LEASE("Attempt to drop lessee %d as master\n", file_priv->master->lessee_id);
+		ret = -EINVAL;
+		goto out_unlock;
+	}
+
 	ret = 0;
 	drm_drop_master(dev, file_priv);
 out_unlock: