virt: vbox: Fix guest capabilities mask check

Check the passed in capabilities against VMMDEV_GUEST_CAPABILITIES_MASK
instead of against VMMDEV_EVENT_VALID_EVENT_MASK.
This tightens the allowed mask from 0x7ff to 0x7.

Fixes: 0ba002bc43 ("virt: Add vboxguest driver for Virtual Box Guest integration")
Cc: stable@vger.kernel.org
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20200709120858.63928-3-hdegoede@redhat.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/virt/vboxguest/vboxguest_core.c

@@ -1444,7 +1444,7 @@ static int vbg_ioctl_change_guest_capabilities(struct vbg_dev *gdev,
 	or_mask = caps->u.in.or_mask;
 	not_mask = caps->u.in.not_mask;
 
-	if ((or_mask | not_mask) & ~VMMDEV_EVENT_VALID_EVENT_MASK)
+	if ((or_mask | not_mask) & ~VMMDEV_GUEST_CAPABILITIES_MASK)
 		return -EINVAL;
 
 	ret = vbg_set_session_capabilities(gdev, session, or_mask, not_mask,

drivers/virt/vboxguest/vmmdev.h

@@ -206,6 +206,8 @@ VMMDEV_ASSERT_SIZE(vmmdev_mask, 24 + 8);
  * not.
  */
 #define VMMDEV_GUEST_SUPPORTS_GRAPHICS                      BIT(2)
+/* The mask of valid capabilities, for sanity checking. */
+#define VMMDEV_GUEST_CAPABILITIES_MASK                      0x00000007U
 
 /** struct vmmdev_hypervisorinfo - Hypervisor info structure. */
 struct vmmdev_hypervisorinfo {