[PATCH v2] drm: check for NULL parameter in exported drm_get_format_name() function.

From: Liviu Dudau
Date: Wed Nov 23 2016 - 05:52:29 EST

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@xxxxxxxxxxxx>
Cc: Rob Clark <robdclark@xxxxxxxxx>
Cc: Jani Nikula <jani.nikula@xxxxxxxxx>
Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>

Signed-off-by: Liviu Dudau <Liviu.Dudau@xxxxxxx>
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),