Good idea!
> From: "Thomas Zimmermann"<tzimmerm...@suse.de>
> Date: Thu, Nov 2, 2023, 21:27
> Subject: Re: [PATCH] gpu/drm/drm_framebuffer.c: Use Macro instead of actual
> number.
> To: "Peng Hao"<peng...@dingdao.com>, <maarten.lankho...@linux.intel.com>,
> <mrip...@kernel.org>, <airl...@gmail.com>, <dan...@ffwll.ch>
> Cc: <linux-ker...@vger.kernel.org>, <dri-devel@lists.freedesktop.org>
> Hi
>
> Am 02.11.23 um 03:29 schrieb Peng Hao:
> > Use Macro DRM_FORMAT_MAX_PLANES instead of 4, to improve modifiability.
> >
> > Signed-off-by: Peng Hao <peng...@dingdao.com>
> > ---
> > drivers/gpu/drm/drm_framebuffer.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/drm_framebuffer.c
> > b/drivers/gpu/drm/drm_framebuffer.c
> > index 2dd97473ca10..bf283dae9090 100644
> > --- a/drivers/gpu/drm/drm_framebuffer.c
> > +++ b/drivers/gpu/drm/drm_framebuffer.c
> > @@ -254,7 +254,7 @@ static int framebuffer_check(struct drm_device *dev,
> > }
> > }
> >
> > - for (i = info->num_planes; i < 4; i++) {
> > + for (i = info->num_planes; i < DRM_FORMAT_MAX_PLANES; i++) {
>
> This change makes the code more fragile. '4' is a fixed constant in the
> UAPI struct, while DRM_FORMAT_MAX_PLANES is an internal constant. I
> agree that both should reasonably have the same value. But (potentially)
> changing the value of DRM_FORMAT_MAX_PLANES will break these loops with
> a possible OOB access.
>
> To make make this code more robust, it might be better to rewrite the
> tests like this
>
> for (i = num_planes; i < ARRAY_SIZE(r->modifier); +i) {
> // the test for modifier[i]
> }
>
> if (r->flags & DRM_MODE_FB_MODIFIERS) {
> for (i < ARRAY_SIZE(handles)) {
> // test for handles[i]
> }
> for (i < ARRAY_SIZE(pitches)) {
> // test for pitches[i]
> }
> for (i < ARRAY_SIZE(offsets)) {
> // test for offsets[i]
> }
> }
>
> Best regards
> Thomas
>
> > if (r->modifier[i]) {
> > drm_dbg_kms(dev, "non-zero modifier for unused plane
> > %d\n", i);
> > return -EINVAL;
>
> --
> Thomas Zimmermann
> Graphics Driver Developer
> SUSE Software Solutions Germany GmbH
> Frankenstrasse 146, 90461 Nuernberg, Germany
> GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
> HRB 36809 (AG Nuernberg)
