[Intel-gfx] [PATCH 1/8] drm/edid: Check the number of detailed timing descriptors in the CEA ext block

[Daniel Vetter]

On Fri, Jan 24, 2020 at 10:02:24PM +0200, Ville Syrjala wrote:
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> CEA-861 says :
> "d = offset for the byte following the reserved data block.
>  If no data is provided in the reserved data block, then d=4.
>  If no DTDs are provided, then d=0."
> 
> So let's not look for DTDs when d==0. In fact let's just make that
> <4 since those values would just mean that he DTDs overlap the block
> header. And let's also check that d isn't so big as to declare
> the descriptors to live past the block end, although the code
> does already survive that case as we'd just end up with a negative
> number of descriptors and the loop would not do anything.
> 
> Cc: Allen Chen <allen.chen at ite.com.tw>
> Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>

Hm I think edid parsing is like the perfect use-case for some in-kernel
unit tests ... In case anyone feels motivated?
-Daniel

> ---
>  drivers/gpu/drm/drm_edid.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> index 99769d6c9f84..1b6e544cf5c7 100644
> --- a/drivers/gpu/drm/drm_edid.c
> +++ b/drivers/gpu/drm/drm_edid.c
> @@ -2201,10 +2201,13 @@ typedef void detailed_cb(struct detailed_timing *timing, void *closure);
>  static void
>  cea_for_each_detailed_block(u8 *ext, detailed_cb *cb, void *closure)
>  {
> -	int i, n = 0;
> +	int i, n;
>  	u8 d = ext[0x02];
>  	u8 *det_base = ext + d;
>  
> +	if (d < 4 || d > 127)
> +		return;
> +
>  	n = (127 - d) / 18;
>  	for (i = 0; i < n; i++)
>  		cb((struct detailed_timing *)(det_base + 18 * i), closure);
> -- 
> 2.24.1
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch