[PATCH] gpu: drm: qxl: Fix possible null-pointer dereferences in qxl_crtc_atomic_flush()

[Jia-Ju Bai <baijiaju1990@gmail.com>]

In qxl_crtc_atomic_flush(), there is an if statement on line 376 to
check whether crtc->state is NULL:
    if (crtc->state && crtc->state->event)

When crtc->state is NULL and qxl_crtc_update_monitors_config() is call, 
qxl_crtc_update_monitors_config() uses crtc->state on line 326:
    if (crtc->state->active)
and on line 358:
    DRM_DEBUG_KMS(..., crtc->state->active, ...);

Thus, possible null-pointer dereferences may occur.

To fix these bugs, crtc->state is checked before calling
qxl_crtc_update_monitors_config().

These bugs are found by a static analysis tool STCheck written by us.

Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
---
 drivers/gpu/drm/qxl/qxl_display.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/qxl/qxl_display.c b/drivers/gpu/drm/qxl/qxl_display.c
index 8b319ebbb0fb..fae18ef1ba59 100644
--- a/drivers/gpu/drm/qxl/qxl_display.c
+++ b/drivers/gpu/drm/qxl/qxl_display.c
@@ -382,7 +382,8 @@ static void qxl_crtc_atomic_flush(struct drm_crtc *crtc,
 		spin_unlock_irqrestore(&dev->event_lock, flags);
 	}
 
-	qxl_crtc_update_monitors_config(crtc, "flush");
+	if (crtc->state)
+		qxl_crtc_update_monitors_config(crtc, "flush");
 }
 
 static void qxl_crtc_destroy(struct drm_crtc *crtc)
-- 
2.17.0