Re: [PATCH 1/4] drm/i915: Sanity check DP AUX message buffer and size

[David Weinehall <david.weinehall@linux.intel.com>]

On Fri, Jan 29, 2016 at 02:52:26PM +0200, Imre Deak wrote:
> While we are calling intel_dp_aux_transfer() with msg->size=0 whenever
> msg->buffer is NULL, passing NULL to memcpy() is undefined according to
> the ISO C standard. I haven't found any notes about this in the GNU C's
> or the kernel's documentation of the function and can't imagine what it
> would do with the NULL ptr. To better document this use of the
> parameters it still make sense to add an explicit check for this to the
> code.
> 
> Caught by Coverity.
> 
> Signed-off-by: Imre Deak <imre.deak@intel.com>

Reviewed-by: David Weinehall <david.weinehall@intel.com>

> ---
>  drivers/gpu/drm/i915/intel_dp.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index e2bea710..2aed36e 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -979,7 +979,10 @@ intel_dp_aux_transfer(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
>  		if (WARN_ON(txsize > 20))
>  			return -E2BIG;
>  
> -		memcpy(txbuf + HEADER_SIZE, msg->buffer, msg->size);
> +		if (msg->buffer)
> +			memcpy(txbuf + HEADER_SIZE, msg->buffer, msg->size);
> +		else
> +			WARN_ON(msg->size);
>  
>  		ret = intel_dp_aux_ch(intel_dp, txbuf, txsize, rxbuf, rxsize);
>  		if (ret > 0) {
> -- 
> 2.5.0
> 
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