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

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Message-ID: <20210720171927.joohdb6lykm7j64t@ldmartin-desk2>
Date:   Tue, 20 Jul 2021 10:19:27 -0700
From:   Lucas De Marchi <lucas.demarchi@...el.com>
To:     Colin King <colin.king@...onical.com>
Cc:     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>,
        Anusha Srivatsa <anusha.srivatsa@...el.com>,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next] drm/i915/xelpd: Fix unsigned compared to less than
 zero error

On Tue, Jul 20, 2021 at 04:57:26PM +0100, Colin King wrote:
>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>


Reviewed-by: Lucas De Marchi <lucas.demarchi@...el.com>

thanks
Lucas De Marchi

>---
> 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
>