[Intel-gfx] [PATCH 1/2] drm/i915: Prevent use-after-free of inherited framebuffer

[Chris Wilson]

During KMS takeover, we try to capture the current configuration and
preserve it across our initialisation. For a variety of reasons, we may
fail this, for example if the current mode was using the legacy VGA
plane. Under such circumstances, we discard the fb in the plane config
and tried to find a matching fb on another CRTC. This obviously also
failed, leaving the plane config fb dangling, pointing to the freed block.

Regression from
commit 484b41dd70a9fbea894632d8926bbb93f05021c7
Author: Jesse Barnes <jbarnes at virtuousgeek.org>
Date:   Fri Mar 7 08:57:55 2014 -0800

    drm/i915: remove early fb allocation dependency on CONFIG_FB v2

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=75963
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/intel_display.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 6e9f189765f6..c3864d1bc62f 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -2125,6 +2125,7 @@ static void intel_find_plane_obj(struct intel_crtc *intel_crtc,
 		return;
 
 	kfree(intel_crtc->base.fb);
+	intel_crtc->base.fb = NULL;
 
 	/*
 	 * Failed to alloc the obj, check to see if we should share
-- 
1.9.0