linux-kernel - [PATCH 5.15 079/177] drm/i915/display: Fix an unsigned subtraction which can never be negative.

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Date:   Mon, 20 Dec 2021 15:33:49 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Harshit Mogalapalli <harshit.m.mogalapalli@...cle.com>,
        Lucas De Marchi <lucas.demarchi@...el.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.15 079/177] drm/i915/display: Fix an unsigned subtraction which can never be negative.

From: Harshit Mogalapalli <harshit.m.mogalapalli@...cle.com>

[ Upstream commit 53b3495273282aa844c4613d19c3b30558c70c84 ]

smatch warning:
drivers/gpu/drm/i915/display/intel_dmc.c:601 parse_dmc_fw() warn:
unsigned 'fw->size - offset' is never less than zero

Firmware size is size_t and offset is u32. So the subtraction is
unsigned which can never be less than zero.

Fixes: 3d5928a168a9 ("drm/i915/xelpd: Pipe A DMC plugging")
Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@...cle.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@...el.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@...el.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211210044129.12422-1-harshit.m.mogalapalli@oracle.com
(cherry picked from commit 87bb2a410dcfb617b88e4695edf4beb6336dc314)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@...el.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/gpu/drm/i915/display/intel_dmc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dmc.c b/drivers/gpu/drm/i915/display/intel_dmc.c
index b3c8e1c450efb..73076737add75 100644
--- a/drivers/gpu/drm/i915/display/intel_dmc.c
+++ b/drivers/gpu/drm/i915/display/intel_dmc.c
@@ -606,7 +606,7 @@ static void parse_dmc_fw(struct drm_i915_private *dev_priv,
 			continue;
 
 		offset = readcount + dmc->dmc_info[id].dmc_offset * 4;
-		if (fw->size - offset < 0) {
+		if (offset > fw->size) {
 			drm_err(&dev_priv->drm, "Reading beyond the fw_size\n");
 			continue;
 		}
-- 
2.33.0