Patch "drm/fb_helper: Fix references to dev->mode_config.num_connector" has been added to the 3.14-stable tree

This is a note to let you know that I've just added the patch titled

    drm/fb_helper: Fix references to dev->mode_config.num_connector

to the 3.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
drm-fb_helper-fix-references-to-dev-mode_config.num_connector.patch
and it can be found in the queue-3.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Lyude <[email protected]>
Date: Thu, 12 May 2016 10:56:59 -0400
Subject: drm/fb_helper: Fix references to dev->mode_config.num_connector

From: Lyude <[email protected]>

commit 255f0e7c418ad95a4baeda017ae6182ba9b3c423 upstream.

During boot, MST hotplugs are generally expected (even if no physical hotplugging occurs) and result in DRM's connector topology changing. This means that using num_connector from the current mode configuration can lead to the number of connectors changing under us. This can lead to some nasty scenarios in fbcon:

- We allocate an array to the size of dev->mode_config.num_connectors.
- MST hotplug occurs, dev->mode_config.num_connectors gets incremented.
- We try to loop through each element in the array using the new value of dev->mode_config.num_connectors, and end up going out of bounds since dev->mode_config.num_connectors is now larger then the array we allocated.

fb_helper->connector_count however, will always remain consistent while we do a modeset in fb_helper.

Note: This is just polish for 4.7, Dave Airlie's drm_connector refcounting fixed these bugs for real. But it's good enough duct-tape for stable kernel backporting, since backporting the refcounting changes is way too invasive.

[danvet: Clarify why we need this. Also remove the now unused "dev" local variable to appease gcc.]

---
 drivers/gpu/drm/drm_fb_helper.c |    5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

@@ -1347,7 +1347,6 @@ static int drm_pick_crtcs(struct drm_fb_
 			  int n, int width, int height)
 {
 	int c, o;
-	struct drm_device *dev = fb_helper->dev;
 	struct drm_connector *connector;
 	struct drm_connector_helper_funcs *connector_funcs;
 	struct drm_encoder *encoder;

@@ -1366,7 +1365,7 @@ static int drm_pick_crtcs(struct drm_fb_
 	if (modes[n] == NULL)
 		return best_score;
 
-	crtcs = kzalloc(dev->mode_config.num_connector *
+	crtcs = kzalloc(fb_helper->connector_count *
 			sizeof(struct drm_fb_helper_crtc *), GFP_KERNEL);
 	if (!crtcs)
 		return best_score;

@@ -1412,7 +1411,7 @@ static int drm_pick_crtcs(struct drm_fb_
 		if (score > best_score) {
 			best_score = score;
 			memcpy(best_crtcs, crtcs,
-			       dev->mode_config.num_connector *
+			       fb_helper->connector_count *
 			       sizeof(struct drm_fb_helper_crtc *));
 		}
 	}

Patches currently in stable-queue which might be from [email protected] are

queue-3.14/drm-fb_helper-fix-references-to-dev-mode_config.num_connector.patch