linux-kernel - [PATCH][next] drm/i915/xelpd: Fix unsigned compared to less than zero error

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Date:   Tue, 20 Jul 2021 16:57:26 +0100
From:   Colin King <colin.king@...onical.com>
To:     Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Lucas De Marchi <lucas.demarchi@...el.com>,
        Anusha Srivatsa <anusha.srivatsa@...el.com>,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH][next] drm/i915/xelpd: Fix unsigned compared to less than zero error

From: Colin Ian King <colin.king@...onical.com>

The subtraction of fw->size - offset is operating on two unsigned
integers and the result is unsigned and hence the less than zero
comparison will always to be false. Fix this by casting fw->size
from a size_t to a ssize_t to ensure the result can be signed to
allow a less than zero result.

Addresses-Coverity: ("Unsigned compared against 0")
Fixes: 3d5928a168a9 ("drm/i915/xelpd: Pipe A DMC plugging")
Signed-off-by: Colin Ian King <colin.king@...onical.com>
---
 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 f8789d4543bf..dde1f243d375 100644
--- a/drivers/gpu/drm/i915/display/intel_dmc.c
+++ b/drivers/gpu/drm/i915/display/intel_dmc.c
@@ -645,7 +645,7 @@ 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 ((ssize_t)fw->size - offset < 0) {
 			drm_err(&dev_priv->drm, "Reading beyond the fw_size\n");
 			continue;
 		}
-- 
2.31.1