linux-kernel - [PATCH] i915/intel_tv_get_modes: fix strncpy truncation warning

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Date:   Wed, 11 Jul 2018 09:46:15 +0200
From:   Dominique Martinet <asmadeus@...ewreck.org>
To:     Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>
Cc:     David Airlie <airlied@...ux.ie>, intel-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Dominique Martinet <asmadeus@...ewreck.org>
Subject: [PATCH] i915/intel_tv_get_modes: fix strncpy truncation warning

This is effectively no-op as the next line writes a nul at the final
byte of the buffer, so copying one letter less does not change the
behaviour.

Signed-off-by: Dominique Martinet <asmadeus@...ewreck.org>
---

gcc 8 gives the following warning, which I am not sure why is treated
as error for this file, thus making me fix it:
drivers/gpu/drm/i915/intel_tv.c: In function ‘intel_tv_get_modes’:
drivers/gpu/drm/i915/intel_tv.c:1358:3: error: ‘strncpy’ specified bound 32 equals destination size [-Werror=stringop-truncation]
   strncpy(mode_ptr->name, input->name, DRM_DISPLAY_MODE_LEN);
   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors


Also, as a side note, while checking if this was already sent I stumbled
uppon this: https://lists.freedesktop.org/archives/intel-gfx/2018-July/170638.html
([Intel-gfx] [PATCH i-g-t 6/7] Fix truncate string in the strncpy)
which replaces strncpy(dest, src, sizeof(dest)) by strncpy(dest, src,
strlen(dest))... This isn't for linux but this looks like a pretty bad
idea to me... (I'm not on the list to reply there, sorry)

 drivers/gpu/drm/i915/intel_tv.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_tv.c b/drivers/gpu/drm/i915/intel_tv.c
index b55b5c157e38..f5614d07b10d 100644
--- a/drivers/gpu/drm/i915/intel_tv.c
+++ b/drivers/gpu/drm/i915/intel_tv.c
@@ -1355,7 +1355,7 @@ intel_tv_get_modes(struct drm_connector *connector)
 		mode_ptr = drm_mode_create(connector->dev);
 		if (!mode_ptr)
 			continue;
-		strncpy(mode_ptr->name, input->name, DRM_DISPLAY_MODE_LEN);
+		strncpy(mode_ptr->name, input->name, DRM_DISPLAY_MODE_LEN - 1);
 		mode_ptr->name[DRM_DISPLAY_MODE_LEN - 1] = '\0';
 
 		mode_ptr->hdisplay = hactive_s;
-- 
2.17.1