Re: [PATCH] drm/i915/bios: Fix the sequence size calculations for MIPI seq v3

[Mika Kahola <mika.kahola@intel.com>]

On Thu, 2016-01-14 at 17:12 +0200, Jani Nikula wrote:
> Two errors in a single line. The size was read from the wrong offset,
> and the end index didn't take the five bytes for sequence byte and size
> of sequence into account. Fix it all, and break up the calculations a
> bit to make it clearer.
> 
Tested-by: Mika Kahola <mika.kahola@intel.com>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Reported-by: Mika Kahola <mika.kahola@intel.com>
> Fixes: 2a33d93486f2 ("drm/i915/bios: add support for MIPI sequence block v3")
> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
> ---
>  drivers/gpu/drm/i915/intel_bios.c | 17 ++++++++++++++---
>  1 file changed, 14 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_bios.c b/drivers/gpu/drm/i915/intel_bios.c
> index 12e2f8b8bf9c..bf62a19c8f69 100644
> --- a/drivers/gpu/drm/i915/intel_bios.c
> +++ b/drivers/gpu/drm/i915/intel_bios.c
> @@ -842,6 +842,7 @@ static int goto_next_sequence_v3(const u8 *data, int index, int total)
>  {
>  	int seq_end;
>  	u16 len;
> +	u32 size_of_sequence;
>  
>  	/*
>  	 * Could skip sequence based on Size of Sequence alone, but also do some
> @@ -852,14 +853,24 @@ static int goto_next_sequence_v3(const u8 *data, int index, int total)
>  		return 0;
>  	}
>  
> -	seq_end = index + *((const u32 *)(data + 1));
> +	/* Skip Sequence Byte. */
> +	index++;
> +
> +	/*
> +	 * Size of Sequence. Excludes the Sequence Byte and the size itself,
> +	 * includes MIPI_SEQ_ELEM_END byte, excludes the final MIPI_SEQ_END
> +	 * byte.
> +	 */
> +	size_of_sequence = *((const uint32_t *)(data + index));
> +	index += 4;
> +
> +	seq_end = index + size_of_sequence;
>  	if (seq_end > total) {
>  		DRM_ERROR("Invalid sequence size\n");
>  		return 0;
>  	}
>  
> -	/* Skip Sequence Byte and Size of Sequence. */
> -	for (index = index + 5; index < total; index += len) {
> +	for (; index < total; index += len) {
>  		u8 operation_byte = *(data + index);
>  		index++;
>  


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