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Commit 255f0e7c authored by Lyude's avatar Lyude Committed by Daniel Vetter
Browse files

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



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.

Cc: stable@vger.kernel.org
Signed-off-by: default avatarLyude <cpaul@redhat.com>
[danvet: Clarify why we need this. Also remove the now unused "dev"
local variable to appease gcc.]
Signed-off-by: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1463065021-18280-3-git-send-email-cpaul@redhat.com
parent 14a3842a

drivers/gpu/drm/drm_fb_helper.c

+2 −3
Original line number Diff line number Diff line
@@ -1968,7 +1968,6 @@ 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;
@@ -1987,7 +1986,7 @@ 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;
@@ -2033,7 +2032,7 @@ 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 *));

		}

	}