[PATCH v3 2/2] drm/i915: Fix oops caused by fbdev initialization failure

[Lukas Wunner <lukas@xxxxxxxxx>]

intelfb_create() is called once on driver initialization. If it fails,
ifbdev->helper.fbdev, ifbdev->fb or ifbdev->fb->obj may be NULL.

Further up in the call stack, intel_fbdev_initial_config() calls
intel_fbdev_fini() to tear down the ifbdev on failure. This calls
intel_fbdev_destroy() which dereferences ifbdev->fb. Fix the ensuing
oops.

Also check in these functions if ifbdev is not NULL to avoid oops:

i915_gem_framebuffer_info() is called on access to debugfs file
"i915_gem_framebuffer" and dereferences ifbdev, ifbdev->helper.fb
and ifbdev->helper.fb->obj.

intel_connector_add_to_fbdev() / intel_connector_remove_from_fbdev()
are called when registering / unregistering an mst connector and
dereference ifbdev.

v3: Drop additional null pointer checks in intel_fbdev_set_suspend(),
    intel_fbdev_output_poll_changed() and intel_fbdev_restore_mode()
    since they already check if ifbdev is not NULL, which is sufficient
    now that intel_fbdev_fini() is called on initialization failure.
    (Requested by Daniel Vetter <daniel.vetter@xxxxxxxx>)

Signed-off-by: Lukas Wunner <lukas@xxxxxxxxx>
---
 drivers/gpu/drm/i915/i915_debugfs.c | 24 +++++++++++++-----------
 drivers/gpu/drm/i915/intel_dp_mst.c | 10 ++++++++--
 drivers/gpu/drm/i915/intel_fbdev.c  |  6 ++++--
 3 files changed, 25 insertions(+), 15 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index 038d5c6..411a9c6 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -1877,17 +1877,19 @@ static int i915_gem_framebuffer_info(struct seq_file *m, void *data)
 	struct drm_i915_private *dev_priv = dev->dev_private;
 
 	ifbdev = dev_priv->fbdev;
-	fb = to_intel_framebuffer(ifbdev->helper.fb);
-
-	seq_printf(m, "fbcon size: %d x %d, depth %d, %d bpp, modifier 0x%llx, refcount %d, obj ",
-		   fb->base.width,
-		   fb->base.height,
-		   fb->base.depth,
-		   fb->base.bits_per_pixel,
-		   fb->base.modifier[0],
-		   atomic_read(&fb->base.refcount.refcount));
-	describe_obj(m, fb->obj);
-	seq_putc(m, '\n');
+	if (ifbdev) {
+		fb = to_intel_framebuffer(ifbdev->helper.fb);
+
+		seq_printf(m, "fbcon size: %d x %d, depth %d, %d bpp, modifier 0x%llx, refcount %d, obj ",
+			   fb->base.width,
+			   fb->base.height,
+			   fb->base.depth,
+			   fb->base.bits_per_pixel,
+			   fb->base.modifier[0],
+			   atomic_read(&fb->base.refcount.refcount));
+		describe_obj(m, fb->obj);
+		seq_putc(m, '\n');
+	}
 #endif
 
 	mutex_lock(&dev->mode_config.fb_lock);
diff --git a/drivers/gpu/drm/i915/intel_dp_mst.c b/drivers/gpu/drm/i915/intel_dp_mst.c
index 9d8a5b4..8c4e7df 100644
--- a/drivers/gpu/drm/i915/intel_dp_mst.c
+++ b/drivers/gpu/drm/i915/intel_dp_mst.c
@@ -408,7 +408,10 @@ static void intel_connector_add_to_fbdev(struct intel_connector *connector)
 {
 #ifdef CONFIG_DRM_FBDEV_EMULATION
 	struct drm_i915_private *dev_priv = to_i915(connector->base.dev);
-	drm_fb_helper_add_one_connector(&dev_priv->fbdev->helper, &connector->base);
+
+	if (dev_priv->fbdev)
+		drm_fb_helper_add_one_connector(&dev_priv->fbdev->helper,
+						&connector->base);
 #endif
 }
 
@@ -416,7 +419,10 @@ static void intel_connector_remove_from_fbdev(struct intel_connector *connector)
 {
 #ifdef CONFIG_DRM_FBDEV_EMULATION
 	struct drm_i915_private *dev_priv = to_i915(connector->base.dev);
-	drm_fb_helper_remove_one_connector(&dev_priv->fbdev->helper, &connector->base);
+
+	if (dev_priv->fbdev)
+		drm_fb_helper_remove_one_connector(&dev_priv->fbdev->helper,
+						   &connector->base);
 #endif
 }
 
diff --git a/drivers/gpu/drm/i915/intel_fbdev.c b/drivers/gpu/drm/i915/intel_fbdev.c
index cd345c5..7ccde58 100644
--- a/drivers/gpu/drm/i915/intel_fbdev.c
+++ b/drivers/gpu/drm/i915/intel_fbdev.c
@@ -530,8 +530,10 @@ static void intel_fbdev_destroy(struct drm_device *dev,
 
 	drm_fb_helper_fini(&ifbdev->helper);
 
-	drm_framebuffer_unregister_private(&ifbdev->fb->base);
-	drm_framebuffer_remove(&ifbdev->fb->base);
+	if (ifbdev->fb) {
+		drm_framebuffer_unregister_private(&ifbdev->fb->base);
+		drm_framebuffer_remove(&ifbdev->fb->base);
+	}
 }
 
 /*
-- 
2.1.0

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