Re: [PATCH v2] drm/dp: Fix off-by-one in register cache size

Kees Cook
2022-02-05T01:38:55Z

Ping. This is a OOB read fix. Can something send this to Linus please?

-Kees

On Wed, Jan 05, 2022 at 09:33:10AM -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])
> | ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Cc: Maxime Ripard <mripard@kernel.org>
> Cc: Thomas Zimmermann <tzimmermann@suse.de>
> Cc: David Airlie <airlied@linux.ie>
> Cc: Daniel Vetter <daniel@ffwll.ch>
> Cc: dri-devel@lists.freedesktop.org
> Fixes: e2e16da398d9 ("drm/dp_helper: Add support for Configuring DSC for HDMI2.1 Pcon")
> Cc: stable@vger.kernel.org
> Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
> Link: https://lore.kernel.org/lkml/20211214001849.GA62559@embeddedor/
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
> v1: https://lore.kernel.org/lkml/20211203084333.3105038-1-keescook@chromium.org/
> v2:
> - add reviewed-by
> - add cc:stable
> ---
> include/drm/drm_dp_helper.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
> index 30359e434c3f..472dac376284 100644
> --- a/include/drm/drm_dp_helper.h
> +++ b/include/drm/drm_dp_helper.h
> @@ -456,7 +456,7 @@ struct drm_panel;
> #define DP_FEC_CAPABILITY_1 0x091 /* 2.0 */
>
> /* DP-HDMI2.1 PCON DSC ENCODER SUPPORT */
> -#define DP_PCON_DSC_ENCODER_CAP_SIZE 0xC /* 0x9E - 0x92 */
> +#define DP_PCON_DSC_ENCODER_CAP_SIZE 0xD /* 0x92 through 0x9E */
> #define DP_PCON_DSC_ENCODER 0x092
> # define DP_PCON_DSC_ENCODER_SUPPORTED (1 << 0)
> # define DP_PCON_DSC_PPS_ENC_OVERRIDE (1 << 1)
> --
> 2.30.2
>

--
Kees Cook