Patch "drm/i915/fbdev: Fix num_connector references in intel_fb_initial_config()" has been added to the 4.4-stable tree

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

drm/i915/fbdev: Fix num_connector references in intel_fb_initial_config()

to the 4.4-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-i915-fbdev-fix-num_connector-references-in-intel_fb_initial_config.patch
and it can be found in the queue-4.4 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 10:56:58 -0400
Subject: drm/i915/fbdev: Fix num_connector references in intel_fb_initial_config()

From: Lyude <[email protected]>

commit 14a3842a1d5945067d1dd0788f314e14d5b18e5b upstream.

During boot time, MST devices usually send a ton of hotplug events irregardless of whether or not any physical hotplugs actually occurred. Hotplugs mean connectors being created/destroyed, and the number of DRM connectors changing under us. This isn't a problem if we use fb_helper->connector_count since we only set it once in the code, however if we use num_connector from struct drm_mode_config we risk it's value changing under us. On top of that, there's even a chance that dev->mode_config.num_connector != fb_helper->connector_count. If the number of connectors happens to increase under us, we'll end up using the wrong array size for memcpy and start writing beyond the actual length of the array, occasionally resulting in kernel panics.

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.

---
 drivers/gpu/drm/i915/intel_fbdev.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

@@ -362,12 +362,12 @@ static bool intel_fb_initial_config(stru
 	uint64_t conn_configured = 0, mask;
 	int pass = 0;
 
-	save_enabled = kcalloc(dev->mode_config.num_connector, sizeof(bool),
+	save_enabled = kcalloc(fb_helper->connector_count, sizeof(bool),
 			       GFP_KERNEL);
 	if (!save_enabled)
 		return false;
 
-	memcpy(save_enabled, enabled, dev->mode_config.num_connector);
+	memcpy(save_enabled, enabled, fb_helper->connector_count);
 	mask = (1 << fb_helper->connector_count) - 1;
 retry:
 	for (i = 0; i < fb_helper->connector_count; i++) {

@@ -501,7 +501,7 @@ retry:
 	if (fallback) {
 bail:
 		DRM_DEBUG_KMS("Not using firmware configuration\n");
-		memcpy(enabled, save_enabled, dev->mode_config.num_connector);
+		memcpy(enabled, save_enabled, fb_helper->connector_count);
 		kfree(save_enabled);
 		return false;
 	}

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

queue-4.4/drm-i915-fbdev-fix-num_connector-references-in-intel_fb_initial_config.patch queue-4.4/drm-fb_helper-fix-references-to-dev-mode_config.num_connector.patch queue-4.4/drm-atomic-verify-connector-funcs-null-when-clearing-states.patch