There is a comment here which says that DIV_ROUND_UP() and that's where
the problem comes from. Say you pick:
args->bpp = UINT_MAX - 7;
args->width = 4;
args->height = 1;
The integer overflow in DIV_ROUND_UP() means "cpp" is UINT_MAX / 8 and
because of how we picked args->width that means cpp < UINT_MAX / 4.
I've fixed it by preventing the integer overflow in DIV_ROUND_UP(). I
removed the check for !cpp because it's not possible after this change.
I also changed all the 0xffffffffU references to U32_MAX.
Signed-off-by: Dan Carpenter <dan.carpen...@oracle.com>
---
v2: additional cleanups
diff --git a/drivers/gpu/drm/drm_dumb_buffers.c
b/drivers/gpu/drm/drm_dumb_buffers.c
index 39ac15ce4702..9e2ae02f31e0 100644
--- a/drivers/gpu/drm/drm_dumb_buffers.c
+++ b/drivers/gpu/drm/drm_dumb_buffers.c
@@ -65,12 +65,13 @@ int drm_mode_create_dumb_ioctl(struct drm_device *dev,
return -EINVAL;
/* overflow checks for 32bit size calculations */
- /* NOTE: DIV_ROUND_UP() can overflow */
+ if (args->bpp > U32_MAX - 8)
+ return -EINVAL;
cpp = DIV_ROUND_UP(args->bpp, 8);
- if (!cpp || cpp > 0xffffffffU / args->width)
+ if (cpp > U32_MAX / args->width)
return -EINVAL;
stride = cpp * args->width;
- if (args->height > 0xffffffffU / stride)
+ if (args->height > U32_MAX / stride)
return -EINVAL;
/* test for wrap-around */
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