On distros like SUSE where ssh config dropins in /usr are supported, there's no
need for a symlink in /etc/ssh/ssh_config.d/ that points to the dropin
installed somewhere in /usr (that is not reachable by ssh).
To make it easy to have a workable ssh-generator on various distros,
let's optionally generate the ssh privsep dir via tmpfiles.d/ drop-in.
This enables the concept with a path of /run/sshd/ as default. This is
the path Debian/Ubuntu uses, and means that we just work on those
distros. Debian/Ubuntu is the only distro (apparently?) that puts the
privsep dir under /run/, hence always needs the dir to be created
manually. Other distros don't need it that much, because they place the
dir in /usr/ (fedora, best choice!) or /var/ (others, not ideal, because
still mutable).
Also adds a longer explanation about this in NEWS, in the hope that
distro maintaines read that and maybe start cleaning this up.
Alternative to: #31543
This adds a tiny binary that is hooked into SSH client config via
ProxyCommand and which simply connects to an AF_UNIX or AF_VSOCK socket
of choice.
The syntax is as simple as this:
ssh unix/some/path # (this connects to AF_UNIX socket /some/path)
or:
ssh vsock/4711
I used "/" as separator of the protocol ID and the value since ":" is
already taken by SSH itself when doing sftp. And "@" is already taken
for separating the user name.
