The new S-S-D would not work with CRUX since for example exim uses
a PID file with root:mail and then there is a root!=mail mismatch.
The manual says
Warning: using this match option with a world-writable pidfile
or using it alone with a daemon that writes the pidfile as an
unprivileged (non-root) user will be refused with an error
(since version 1.19.3) as this is a security risk, because
either any user can write to it, or if the daemon gets
compromised, the contents of the pidfile cannot be trusted, and
then a privileged runner (such as an init script executed as
root) would end up acting on any system process. Using
/dev/null is exempt from these checks.
The actual code contradicts this as the mail group in our example
cannot write the PID file, only read it.
I thus have adjusted the code to only refuse the operation if the
group can write the file, too.
(Maybe this is even a "bug" that should be reported upstream?)
