is ut_user[] in struct utmpx NUL terminated?

[Don Lewis]

On 16 May, Ed Schouten wrote:
> Hi Don,
> 
> 2016-05-16 1:07 GMT+02:00 Don Lewis <truckman at freebsd.org>:
>> There is a lot of code that expects ut_user[] to be NUL terminated.
> 
> Our implementation of utmpx should be pretty friendly to use:
> 
> - You can call pututxline() with strings that are not null terminated.
> - The getutx*() functions return entries in which all strings are null
> terminated.

The latter doesn't appear to be true.  If I stuff a non-NUL terminated
32 character user name into ut_user and then call pututxline(), it calls
utx_to_futx(), which uses the UTOF_STRING() macro, which in turn uses
snprintf() to copy the data to the corresponding field in a struct futx
before saving the latter.  Going in the other direction, getutxent()
calls futx_to_utx(), which uses the FTOU_STRING() macro, which in turn
uses strncpy() to copy the data back out.  If the original name was 32
characters, then the ut_user value in the returned struct utmpx will not
be NUL terminated.