drm/vmwgfx: limit the number of mip levels in vmw_gb_surface_define_ioctl()

CVE-2017-7346

The 'req->mip_levels' parameter in vmw_gb_surface_define_ioctl() is
a user-controlled 'uint32_t' value which is used as a loop count limit.
This can lead to a kernel lockup and DoS. Add check for 'req->mip_levels'.

References:
https://bugzilla.redhat.com/show_bug.cgi?id=1437431

Cc: <stable@vger.kernel.org>
Signed-off-by: Vladis Dronov <vdronov@redhat.com>
Reviewed-by: Sinclair Yeh <syeh@vmware.com>

(cherry picked from commit ee9c4e68)
Signed-off-by: Po-Hsu Lin <po-hsu.lin@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

drivers/gpu/drm/vmwgfx/vmwgfx_surface.c

@@ -1293,6 +1293,9 @@ int vmw_gb_surface_define_ioctl(struct drm_device *dev, void *data,
 	if (req->multisample_count != 0)
 		return -EINVAL;
 
+	if (req->mip_levels > DRM_VMW_MAX_MIP_LEVELS)
+		return -EINVAL;
+
 	if (unlikely(vmw_user_surface_size == 0))
 		vmw_user_surface_size = ttm_round_pot(sizeof(*user_srf)) +
 			128;