linux-kernel - [PATCH AUTOSEL 4.18 12/45] drm/amd/display: fix bug of accessing invalid memory

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Date:   Sun,  4 Nov 2018 08:52:07 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     stable@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Su Sung Chung <Su.Chung@....com>,
        Alex Deucher <alexander.deucher@....com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH AUTOSEL 4.18 12/45] drm/amd/display: fix bug of accessing invalid memory

From: Su Sung Chung <Su.Chung@....com>

[ Upstream commit 43c3ff27a47d83d153c4adc088243ba594582bf5 ]

[Why]
A loop inside of build_evenly_distributed_points function that traverse through
the array of points become an infinite loop when m_GammaUpdates does not
get assigned to any value.

[How]
In DMColor, clear m_gammaIsValid bit just before writting all Zeromem for
m_GammaUpdates, to prevent calling build_evenly_distributed_points
before m_GammaUpdates gets assigned to some value.

Signed-off-by: Su Sung Chung <Su.Chung@....com>
Reviewed-by: Aric Cyr <Aric.Cyr@....com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@....com>
Signed-off-by: Alex Deucher <alexander.deucher@....com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/gpu/drm/amd/display/modules/color/color_gamma.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/modules/color/color_gamma.c b/drivers/gpu/drm/amd/display/modules/color/color_gamma.c
index eee0dfad6962..7d9fea6877bc 100644
--- a/drivers/gpu/drm/amd/display/modules/color/color_gamma.c
+++ b/drivers/gpu/drm/amd/display/modules/color/color_gamma.c
@@ -968,10 +968,14 @@ static void build_evenly_distributed_points(
 	struct dividers dividers)
 {
 	struct gamma_pixel *p = points;
-	struct gamma_pixel *p_last = p + numberof_points - 1;
+	struct gamma_pixel *p_last;
 
 	uint32_t i = 0;
 
+	// This function should not gets called with 0 as a parameter
+	ASSERT(numberof_points > 0);
+	p_last = p + numberof_points - 1;
+
 	do {
 		struct fixed31_32 value = dc_fixpt_from_fraction(i,
 			numberof_points - 1);
@@ -982,7 +986,7 @@ static void build_evenly_distributed_points(
 
 		++p;
 		++i;
-	} while (i != numberof_points);
+	} while (i < numberof_points);
 
 	p->r = dc_fixpt_div(p_last->r, dividers.divider1);
 	p->g = dc_fixpt_div(p_last->g, dividers.divider1);
-- 
2.17.1