On Wed, May 09, 2018 at 09:18:57AM +0100, Chris Wilson wrote: > Quoting Dan Carpenter (2018-05-09 09:12:54) > > There is a comment here which says that DIV_ROUND_UP() can overflow 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. > > > > Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx> > > --- > > v2: correct a typo in the commit message > > > > diff --git a/drivers/gpu/drm/drm_dumb_buffers.c b/drivers/gpu/drm/drm_dumb_buffers.c > > index 39ac15ce4702..45b0b5bbb5f8 100644 > > --- a/drivers/gpu/drm/drm_dumb_buffers.c > > +++ b/drivers/gpu/drm/drm_dumb_buffers.c > > @@ -65,7 +65,8 @@ 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 > UINT_MAX - 8) > > + return -EINVAL; > > #define __KERNEL_DIV_ROUND_UP(n, d) (((n) + (d) - 1) / (d) > > both args->bpp and cpp are u32, so should we use U32_MAX to be typesafe? > They will always be equivalent so it's just a style issue... I don't have a strong preference so I can use U32_MAX if that's prefered. > > cpp = DIV_ROUND_UP(args->bpp, 8); > > if (!cpp || cpp > 0xffffffffU / args->width) > > And these constants should also be U32_MAX? Yeah. I considered changing those but one never knows how much style to clean up... I'll redo in the respin. regards, dan carpenter -- To unsubscribe from this list: send the line "unsubscribe kernel-janitors" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
