drm/nv50/crtc: Bail out if FB is not bound to crtc

Fixes possbile NULL pointer dereference
Resolves 'kernel crash in nv50_crtc_do_mode_set_base during shutdown'
https://bugs.freedesktop.org/show_bug.cgi?id=40005

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

1 files changed, 10 insertions, 2 deletions

diff --git a/drivers/gpu/drm/nouveau/nv50_crtc.c b/drivers/gpu/drm/nouveau/nv50_crtc.c
index 46ad59ea2185..5d989073ba6e 100644
--- a/drivers/gpu/drm/nouveau/nv50_crtc.c
+++ b/drivers/gpu/drm/nouveau/nv50_crtc.c
@@ -519,12 +519,18 @@ nv50_crtc_do_mode_set_base(struct drm_crtc *crtc,
         struct drm_device *dev = nv_crtc->base.dev;
         struct drm_nouveau_private *dev_priv = dev->dev_private;
         struct nouveau_channel *evo = nv50_display(dev)->master;
-        struct drm_framebuffer *drm_fb = nv_crtc->base.fb;
-        struct nouveau_framebuffer *fb = nouveau_framebuffer(drm_fb);
+        struct drm_framebuffer *drm_fb;
+        struct nouveau_framebuffer *fb;
         int ret;
 
         NV_DEBUG_KMS(dev, "index %d\n", nv_crtc->index);
 
+        /* no fb bound */
+        if (!atomic && !crtc->fb) {
+                NV_DEBUG_KMS(dev, "No FB bound\n");
+                return 0;
+        }
+
         /* If atomic, we want to switch to the fb we were passed, so
          * now we update pointers to do that.  (We don't pin; just
          * assume we're already pinned and update the base address.)
@@ -533,6 +539,8 @@ nv50_crtc_do_mode_set_base(struct drm_crtc *crtc,
                 drm_fb = passed_fb;
                 fb = nouveau_framebuffer(passed_fb);
         } else {
+                drm_fb = crtc->fb;
+                fb = nouveau_framebuffer(crtc->fb);
                 /* If not atomic, we can go ahead and pin, and unpin the
                  * old fb we were passed.
                  */