Re: some sprintf cleanups for "who"

[Jim Meyering]

Paul Eggert <address@hidden> wrote:
> I noticed that who.c's make_id_equals_comment uses sprintf with an
> "%.*s" format to copy a value that might not be null-terminated; this
> results in undefined behavior.  I don't know of any host where it
> doesn't work but it's easy to be safe.
>
> I then audited for other sprintf glitches and/or bugs and propose the
> following patch for them all.  Each hunk is pretty much independent.
>
> 2004-06-13  Paul Eggert  <address@hidden>
>
>       * src/who.c (PIDSTR_DECL_AND_INIT): Don't assume pid_t fits
>       in int.
>       (UT_ID) [!HAVE_STRUCT_XTMP_UT_ID]: Remove bogus comment,
>       as (sizeof "??") reliably returns 3.
>       (print_line): Guard against idle and pid being too long
>       (which is possible when printing headers).
>       (print_user): Allocate enough bytes for idlestr.  Use IDLESTR_LEN.
>       Avoid unnecessary cast of sizeof to int.
>       (make_id_equals_comment): Do not assume that UT_ID returns
>       a string; it might return a non-null-terminated array.
>       Use strncat instead.  It's not very often where
>       strncat is exactly what you want, but this is one of those rare cases.

Applied.  Thanks.