Commit b28cd41f authored Jan 20, 2014 by David Herrmann

drm/crtc: add sanity checks to create_dumb()



Lets make sure some basic expressions are always true:
  bpp != NULL
  width != NULL
  height != NULL
  stride = bpp * width < 2^32
  size = stride * height < 2^32
  PAGE_ALIGN(size) < 2^32

At least the udl driver doesn't check for multiplication-overflows, so
lets just make sure it will never happen. These checks allow drivers to do
any 32bit math without having to test for mult-overflows themselves.

The two divisions might hurt performance a bit, but dumb_create() is only
used for scanout-buffers, so that should be fine. We could use 64bit math
to avoid the divisions, but that may be slow on 32bit machines.. Or maybe
there should just be a "safe_mult32()" helper, which currently doesn't
exist (I think?).

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: David Herrmann <dh.herrmann@gmail.com>

parent 77472347

drivers/gpu/drm/drm_crtc.c

+17 −0

Original line number	Diff line number	Diff line
		@@ -3784,9 +3784,26 @@ int drm_mode_create_dumb_ioctl(struct drm_device *dev,
		void data, struct drm_file file_priv)
		{
		struct drm_mode_create_dumb *args = data;
		u32 cpp, stride, size;

		if (!dev->driver->dumb_create)
		return -ENOSYS;
		if (!args->width \|\| !args->height \|\| !args->bpp)
		return -EINVAL;

		/* overflow checks for 32bit size calculations */
		cpp = DIV_ROUND_UP(args->bpp, 8);
		if (cpp > 0xffffffffU / args->width)
		return -EINVAL;
		stride = cpp * args->width;
		if (args->height > 0xffffffffU / stride)
		return -EINVAL;

		/* test for wrap-around */
		size = args->height * stride;
		if (PAGE_ALIGN(size) == 0)
		return -EINVAL;

		return dev->driver->dumb_create(file_priv, dev, args);
		}