On distros using Debian's base-passwd, the name of the group with gid 65534 is
nogroup. Currently, systemd-sysusers creates a spurious "nobody" group
systemd-sysusers[243]: Creating group nobody with gid 996
That's both confusing and redundant, as the nobody user still has primary group
65534 aka nogroup, and the nobody group simply goes completely unused.
So explicitly specify the primary group of the nobody user, and add a line
ensuring that that group exists.
This is not a problem for Debian (or Ubuntu) itself, as they add their own
version of basic.conf in their systemd build logic. But it appears on for
example Yocto/OpenEmbedded.
The current overflow checking is broken in the corner case of the strings'
combined length being exactly SIZE_MAX: After the loop, l would be SIZE_MAX,
but we're not testing whether the l+1 expression overflows.
Fix it by simply pre-accounting for the final '\0': initialize l to 1 instead
of 0.
The loops over (x, then all varargs, until a NULL is found) can be written much
simpler with an ordinary for loop. Just initialize the loop variable to x, test
that, and in the increment part, fetch the next va_arg(). That removes a level
of indentation, and avoids doing a separate strlen()/stpcpy() call for x.
While touching this code anyway, change (size_t)-1 to the more readable
SIZE_MAX.
Rasmus Villemoes