Call setsid() before executing sandboxed code (CVE-2017-5226)

This prevents the sandboxed code from getting a controlling tty,
which in turn prevents it from accessing the TIOCSTI ioctl and hence
faking terminal input.

Fixes: #142

Closes: #143
Approved by: cgwalters
resolve_symlinks_in_ops (void)
{
  SetupOp *op;

  for (op = ops; op != NULL; op = op->next)
    {
      const char *old_source;

      switch (op->type)
        {
        case SETUP_RO_BIND_MOUNT:
        case SETUP_DEV_BIND_MOUNT:
        case SETUP_BIND_MOUNT:
          old_source = op->source;
          op->source = realpath (old_source, NULL);
          if (op->source == NULL)
            die_with_error ("Can't find source path %s", old_source);
          break;
        default:
          break;
        }
    }
}

resolve_symlinks_in_ops (void)
{
  SetupOp *op;

  for (op = ops; op != NULL; op = op->next)
    {
      const char *old_source;

      switch (op->type)
        {
        case SETUP_RO_BIND_MOUNT:
        case SETUP_DEV_BIND_MOUNT:
        case SETUP_BIND_MOUNT:
          old_source = op->source;
          op->source = realpath (old_source, NULL);
          if (op->source == NULL)
            die_with_error ("Can't find source path %s", old_source);
          break;
        default:
          break;
        }
    }
}
