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 <geert@xxxxxxxxxxxxxx>
---
Why is drm_mode_create_dumb.size __u64? The test for "args->height >
U32_MAX / stride" rejects all sizes not fitting in __u32 anyway.
---
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;
- stride = cpp * args->width;
+ stride = DIV_ROUND_UP(args->bpp * args->width, 8);
if (args->height > U32_MAX / stride)
return -EINVAL;
--
2.34.1
