[PATCH] drm/dp: Fix off-by-one in register cache size

[Kees Cook]

On Mon, Dec 13, 2021 at 06:18:49PM -0600, Gustavo A. R. Silva wrote:
> On Fri, Dec 03, 2021 at 12:43:33AM -0800, Kees Cook wrote:
> > The pcon_dsc_dpcd array holds 13 registers (0x92 through 0x9E). Fix the
> > math to calculate the max size. Found from a -Warray-bounds build:
> > 
> > drivers/gpu/drm/drm_dp_helper.c: In function 'drm_dp_pcon_dsc_bpp_incr':
> > drivers/gpu/drm/drm_dp_helper.c:3130:28: error: array subscript 12 is outside array bounds of 'const u8[12]' {aka 'const unsigned char[12]'} [-Werror=array-bounds]
> >  3130 |         buf = pcon_dsc_dpcd[DP_PCON_DSC_BPP_INCR - DP_PCON_DSC_ENCODER];
> >       |               ~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > drivers/gpu/drm/drm_dp_helper.c:3126:39: note: while referencing 'pcon_dsc_dpcd'
> >  3126 | int drm_dp_pcon_dsc_bpp_incr(const u8 pcon_dsc_dpcd[DP_PCON_DSC_ENCODER_CAP_SIZE])
> >       |                              ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > 
> > Fixes: e2e16da398d9 ("drm/dp_helper: Add support for Configuring DSC for HDMI2.1 Pcon")
> 
> This should be tagged for -stable:
> 
> Cc: stable at vger.kernel.org

Ah yes, thank you! :)

-- 
Kees Cook