drm: fix division-by-zero on dumb_create()

Kinda unexpected, but DIV_ROUND_UP() can overflow if passed an argument
bigger than UINT_MAX - DIVISOR. Fix this by testing for "!cpp" before
using it in the following division.

Note that DIV_ROUND_UP() is defined as:
        #define DIV_ROUND_UP(n,d) (((n) + (d) - 1) / (d))

..this will obviously overflow if (n + d - 1) is bigger than UINT_MAX.

Reported-by: Tommi Rantala <tt.rantala@gmail.com>
Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
Reviewed-by: Rob Clark <robdclark@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
index fa2be249999c..90e773019eac 100644
--- a/drivers/gpu/drm/drm_crtc.c
+++ b/drivers/gpu/drm/drm_crtc.c
@@ -4696,8 +4696,9 @@ int drm_mode_create_dumb_ioctl(struct drm_device *dev,
                 return -EINVAL;
 
         /* overflow checks for 32bit size calculations */
+        /* NOTE: DIV_ROUND_UP() can overflow */
         cpp = DIV_ROUND_UP(args->bpp, 8);
-        if (cpp > 0xffffffffU / args->width)
+        if (!cpp || cpp > 0xffffffffU / args->width)
                 return -EINVAL;
         stride = cpp * args->width;
         if (args->height > 0xffffffffU / stride)