linux-kernel - [PATCH v2] drm: check for NULL parameter in exported drm_get_format

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Message-Id: <20161123105213.27674-1-Liviu.Dudau@arm.com>
Date:   Wed, 23 Nov 2016 10:52:13 +0000
From:   Liviu Dudau <Liviu.Dudau@....com>
To:     Eric Engestrom <eric@...estrom.ch>
Cc:     David Airlie <airlied@...ux.ie>,
        DRI devel <dri-devel@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Rob Clark <robdclark@...il.com>,
        Jani Nikula <jani.nikula@...el.com>,
        Daniel Vetter <daniel.vetter@...ll.ch>
Subject: [PATCH v2] drm: check for NULL parameter in exported drm_get_format_name() function.

drm_get_format_name() de-references the buf parameter without checking
if the pointer was not NULL. Given that the function is EXPORT-ed, lets
sanitise the parameters before proceeding.

v2: Use BUG_ON() to annoy users that did not pass valid parameters to function.

Fixes: b3c11ac267d461d3d5 ("drm: move allocation out of drm_get_format_name())
Cc: Eric Engestrom <eric@...estrom.ch>
Cc: Rob Clark <robdclark@...il.com>
Cc: Jani Nikula <jani.nikula@...el.com>
Cc: Daniel Vetter <daniel.vetter@...ll.ch>

Signed-off-by: Liviu Dudau <Liviu.Dudau@....com>
---
I still think sanity checking the parameters of an exported function is worth
doing, even if the way one triggers the NULL pointer crash is priviledged. Not
a big fan of the verbosity of BUG_ON() and would rather silently reject NULL buf
pointer, but that is a matter of taste.


 drivers/gpu/drm/drm_fourcc.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/gpu/drm/drm_fourcc.c b/drivers/gpu/drm/drm_fourcc.c
index 90d2cc8..6d80239 100644
--- a/drivers/gpu/drm/drm_fourcc.c
+++ b/drivers/gpu/drm/drm_fourcc.c
@@ -85,6 +85,8 @@ EXPORT_SYMBOL(drm_mode_legacy_fb_format);
  */
 const char *drm_get_format_name(uint32_t format, struct drm_format_name_buf *buf)
 {
+	BUG_ON(!buf);
+
 	snprintf(buf->str, sizeof(buf->str),
 		 "%c%c%c%c %s-endian (0x%08x)",
 		 printable_char(format & 0xff),
-- 
2.10.2