linux-kernel - [76/90] drm/i915: Avoid NULL dereference with component_only tv

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Message-Id: <20091217011607.913966145@mini.kroah.org>
Date:	Wed, 16 Dec 2009 17:15:27 -0800
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Chris Wilson <chris@...is-wilson.co.uk>,
	David Woodhouse <dwmw2@...radead.org>,
	Zhenyu Wang <zhenyu.z.wang@...el.com>,
	Zhenyu Wang <zhenyuw@...ux.intel.com>,
	Eric Anholt <eric@...olt.net>
Subject: [76/90] drm/i915: Avoid NULL dereference with component_only tv_modes

2.6.31-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Chris Wilson <chris@...is-wilson.co.uk>

commit d271817baecbccb47da0d9f28c285a0dae8a06b7 upstream.

In commit d2d9f2324, the guard for a valid video mode was removed. This
caused the regression:

  kernel crash during kms graphic boot on Intel GM4500 platform
  https://bugzilla.redhat.com/show_bug.cgi?id=540218

This patches changes the logic slightly not to rely on a coupled
variable, but to just check whether the video_modes is valid before
dereferencing.

Signed-off-by: Chris Wilson <chris@...is-wilson.co.uk>
Cc: David Woodhouse <dwmw2@...radead.org>
Cc: Zhenyu Wang <zhenyu.z.wang@...el.com>
[ickle: Actually reference the correct bug report]
Acked-by: Zhenyu Wang <zhenyuw@...ux.intel.com>
Signed-off-by: Eric Anholt <eric@...olt.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 drivers/gpu/drm/i915/intel_tv.c |   11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

--- a/drivers/gpu/drm/i915/intel_tv.c
+++ b/drivers/gpu/drm/i915/intel_tv.c
@@ -1212,20 +1212,17 @@ intel_tv_mode_set(struct drm_encoder *en
 		tv_ctl |= TV_TRILEVEL_SYNC;
 	if (tv_mode->pal_burst)
 		tv_ctl |= TV_PAL_BURST;
+
 	scctl1 = 0;
-	/* dda1 implies valid video levels */
-	if (tv_mode->dda1_inc) {
+	if (tv_mode->dda1_inc)
 		scctl1 |= TV_SC_DDA1_EN;
-	}
-
 	if (tv_mode->dda2_inc)
 		scctl1 |= TV_SC_DDA2_EN;
-
 	if (tv_mode->dda3_inc)
 		scctl1 |= TV_SC_DDA3_EN;
-
 	scctl1 |= tv_mode->sc_reset;
-	scctl1 |= video_levels->burst << TV_BURST_LEVEL_SHIFT;
+	if (video_levels)
+		scctl1 |= video_levels->burst << TV_BURST_LEVEL_SHIFT;
 	scctl1 |= tv_mode->dda1_inc << TV_SCDDA1_INC_SHIFT;
 
 	scctl2 = tv_mode->dda2_size << TV_SCDDA2_SIZE_SHIFT |


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