drm/irq: Check for valid VBLANK before dereference

When accessing the array of per-CRTC VBLANK structures we must always
check that the index into the array is valid before dereferencing to
avoid crashing.

Signed-off-by: Thierry Reding <treding@nvidia.com>
[danvet: Squash in my own whitespace ocd fixup in drm_vblank_count.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/drm_irq.c

@@ -877,6 +877,7 @@ u32 drm_vblank_count(struct drm_device *dev, int crtc)
 
 	if (WARN_ON(crtc >= dev->num_crtcs))
 		return 0;
+
 	return vblank->count;
 }
 EXPORT_SYMBOL(drm_vblank_count);
@@ -1110,10 +1111,10 @@ void drm_vblank_put(struct drm_device *dev, int crtc)
 {
 	struct drm_vblank_crtc *vblank = &dev->vblank[crtc];
 
-	if (WARN_ON(atomic_read(&vblank->refcount) == 0))
+	if (WARN_ON(crtc >= dev->num_crtcs))
 		return;
 
-	if (WARN_ON(crtc >= dev->num_crtcs))
+	if (WARN_ON(atomic_read(&vblank->refcount) == 0))
 		return;
 
 	/* Last user schedules interrupt disable */
@@ -1158,6 +1159,9 @@ void drm_wait_one_vblank(struct drm_device *dev, int crtc)
 	int ret;
 	u32 last;
 
+	if (WARN_ON(crtc >= dev->num_crtcs))
+		return;
+
 	ret = drm_vblank_get(dev, crtc);
 	if (WARN(ret, "vblank not available on crtc %i, ret=%i\n", crtc, ret))
 		return;
@@ -1428,6 +1432,9 @@ void drm_vblank_post_modeset(struct drm_device *dev, int crtc)
 	if (!dev->num_crtcs)
 		return;
 
+	if (WARN_ON(crtc >= dev->num_crtcs))
+		return;
+
 	if (vblank->inmodeset) {
 		spin_lock_irqsave(&dev->vbl_lock, irqflags);
 		dev->vblank_disable_allowed = true;