Hi Am 24.08.23 um 17:08 schrieb Geert Uytterhoeven:
drm_mode_create_dumb() calculates the number of characters per pixel from the number of bits per pixel by rounding up, which is not correct as the actual value of cpp may be non-integer. While we do not need to care here about complex formats like YUV, bpp < 8 is a valid use case.- The overflow check for the buffer width is not correct if bpp < 8. However, it doesn't hurt, as widths larger than U32_MAX / 8 should not happen for real anyway. Add a comment to clarify. - Calculating the stride from the number of characters per pixel is not correct. Fix this by calculating it from the number of bits per pixel instead. Signed-off-by: Geert Uytterhoeven <ge...@linux-m68k.org> Reviewed-by: Javier Martinez Canillas <javi...@redhat.com> Tested-by: Javier Martinez Canillas <javi...@redhat.com> --- v2: - Add Reviewed-by, Tested-by. --- drivers/gpu/drm/drm_dumb_buffers.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/gpu/drm/drm_dumb_buffers.c b/drivers/gpu/drm/drm_dumb_buffers.c index 70032bba1c97e787..21a04c32a5e3d785 100644 --- a/drivers/gpu/drm/drm_dumb_buffers.c +++ b/drivers/gpu/drm/drm_dumb_buffers.c @@ -71,10 +71,11 @@ int drm_mode_create_dumb(struct drm_device *dev, /* overflow checks for 32bit size calculations */ if (args->bpp > U32_MAX - 8) return -EINVAL; + /* Incorrect (especially if bpp < 8), but doesn't hurt much */ cpp = DIV_ROUND_UP(args->bpp, 8); if (cpp > U32_MAX / args->width) return -EINVAL;
At first, I was confused by this. So I'd really prefer to outright delete this code. As you say, it's incorrect and doesn't add anything. The concept of cpp is somewhat wrong anyway.
- stride = cpp * args->width; + stride = DIV_ROUND_UP(args->bpp * args->width, 8);
Do we need an overflow check for (bpp * width < U32_MAX) ? Best regards Thomas
if (args->height > U32_MAX / stride)
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)
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