101       *buffer_size = size_needed;
    102       new_buf = (char *) realloc (*buffer, *buffer_size);
    103
    104       if (new_buf == NULL)
    105         {
    ...
    114           goto done;
    115         }

It's a shame they put that "..." there, because this looked like another potential vulnerability to me, or at least something I would take very critically reading this code. (realloc fails, the caller's variable at buffer_size still gets assigned a larger value, next call thinks it has a larger buffer than it does). Line 110 assigns *buffer_size back to 0 so there is no such problem.

From this, the vulnerability was fixed in May 2013 so any systems from there or later (e.g. Ubuntu 14.04) are fine. Older systems obviously now need to wait for the patches to come through.

If you are looking for date-based checking[1], August 2013 is when glibc 2.18 was released.[2]

[1] I wouldn't.

[2] http://ftp.gnu.org/gnu/glibc/

Most importantly, it contains a test program at the beginning of section 4.