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From:   Keith Packard <keithp@keithp.com>
To:     linux-kernel@vger.kernel.org, Dave Airlie <airlied@redhat.com>,
        Daniel Vetter <daniel@ffwll.ch>
Cc:     Keith Packard <keithp@keithp.com>, dri-devel@lists.freedesktop.org
Subject: [PATCH] drm: Check for lessee in DROP_MASTER ioctl
Date:   Thu, 18 Jan 2018 17:51:59 -0800
Message-Id: <20180119015159.1606-1-keithp@keithp.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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

diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c
index aad468d170a7..d9c0f7573905 100644
--- a/drivers/gpu/drm/drm_auth.c
+++ b/drivers/gpu/drm/drm_auth.c
@@ -230,6 +230,12 @@ int drm_dropmaster_ioctl(struct drm_device *dev, void *data,
 	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:
-- 
2.15.1