[4.2.y-ckt stable] Patch "drm/fb_helper: Fix references to dev->mode_config.num_connector" has been added to the 4.2.y-ckt tree

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

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

to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree 
which can be found at:

    https://git.launchpad.net/~canonical-kernel/linux/+git/linux-stable-ckt/log/?h=linux-4.2.y-queue

This patch is scheduled to be released in version 4.2.8-ckt12.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 4.2.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

---8<------------------------------------------------------------

>From bc39badb1c2cfd42ffb7f8f642b0c1c50b73a976 Mon Sep 17 00:00:00 2001
From: Lyude <cpaul at redhat.com>
Date: Thu, 12 May 2016 10:56:59 -0400
Subject: drm/fb_helper: Fix references to dev->mode_config.num_connector

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.

Signed-off-by: Lyude <cpaul at redhat.com>
[danvet: Clarify why we need this. Also remove the now unused "dev"
local variable to appease gcc.]
Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1463065021-18280-3-git-send-email-cpaul@redhat.com
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/gpu/drm/drm_fb_helper.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index cac4229..c8b90b3 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -1549,7 +1549,6 @@ static int drm_pick_crtcs(struct drm_fb_helper *fb_helper,
 			  int n, int width, int height)
 {
 	int c, o;
-	struct drm_device *dev = fb_helper->dev;
 	struct drm_connector *connector;
 	const struct drm_connector_helper_funcs *connector_funcs;
 	struct drm_encoder *encoder;
@@ -1568,7 +1567,7 @@ static int drm_pick_crtcs(struct drm_fb_helper *fb_helper,
 	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;
@@ -1614,7 +1613,7 @@ static int drm_pick_crtcs(struct drm_fb_helper *fb_helper,
 		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 *));
 		}
 	}
--
2.7.4