[PATCH] drm: Fixes unsafe deference in locks.

[Peter Antoine <peter.antoine@intel.com>]

This patch fixes an unsafe deference in the DRM_IOCTL_NEW_CTX. If the
ioctl is called before the lock is created or after it has been destroyed.
The code will deference a NULL pointer. This ioctl is a root ioctl so
exploitation is limited.

Issue: GMINL-7409
Change-Id: Icabf814abe8225d616fdf4f981cd36d2b27f7ad5
Signed-off-by: Peter Antoine <peter.antoine@intel.com>
---
 drivers/gpu/drm/drm_context.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_context.c b/drivers/gpu/drm/drm_context.c
index a4b017b..4754e79 100644
--- a/drivers/gpu/drm/drm_context.c
+++ b/drivers/gpu/drm/drm_context.c
@@ -252,7 +252,13 @@ static int drm_context_switch_complete(struct drm_device *dev,
 {
 	dev->last_context = new;	/* PRE/POST: This is the _only_ writer. */
 
-	if (!_DRM_LOCK_IS_HELD(file_priv->master->lock.hw_lock->lock)) {
+	if (file_priv->master->lock.hw_lock == NULL) {
+		DRM_ERROR(
+			"Device has been unregistered. Hard exit. Process %d\n",
+			task_pid_nr(current));
+		send_sig(SIGTERM, current, 0);
+		return -EINTR;
+	} else if (!_DRM_LOCK_IS_HELD(file_priv->master->lock.hw_lock->lock)) {
 		DRM_ERROR("Lock isn't held after context switch\n");
 	}
 
-- 
1.9.1

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