Re: [PATCH] systemd: Also clear LISTEN_FDNAMES during systemd socket activation

[Eric Blake]

On Mon, Mar 27, 2023 at 10:15:06AM +0100, Daniel P. Berrangé wrote:
> On Fri, Mar 24, 2023 at 10:33:49AM -0500, Eric Blake wrote:
> > Some time after systemd documented LISTEN_PID and LISTEN_FDS for
> > socket activation, they later added LISTEN_FDNAMES; now documented at:
> > https://www.freedesktop.org/software/systemd/man/sd_listen_fds.html
> > 
> > In particular, look at the implementation of sd_listen_fds_with_names():
> > https://github.com/systemd/systemd/blob/main/src/libsystemd/sd-daemon/sd-daemon.c
> > 
> > If we ever pass LISTEN_PID=xxx and LISTEN_FDS=n to a child process,
> > but leave LISTEN_FDNAMES=... unchanged as inherited from our parent
> > process, then our child process using sd_listen_fds_with_names() might
> > see a mismatch in the number of names (unexpected -EINVAL failure), or
> > even if the number of names matches the values of those names may be
> > unexpected (with even less predictable results).
> > 
> > Usually, this is not an issue - the point of LISTEN_PID is to tell
> > systemd socket activation to ignore all other LISTEN_* if they were
> > not directed to this particular pid.  But if we end up consuming a
> > socket directed to this qemu process, and later decide to spawn a
> > child process that also needs systemd socket activation, we must
> > ensure we are not leaking any stale systemd variables through to that
> > child.  The easiest way to do this is to wipe ALL LISTEN_* variables
> > at the time we consume a socket, even if we do not yet care about a
> > LISTEN_FDNAMES passed in from the parent process.
> > 
> > See also 
> > https://lists.freedesktop.org/archives/systemd-devel/2023-March/048920.html
> > 
> > Thanks: Laszlo Ersek <lersek@redhat.com>
> > Signed-off-by: Eric Blake <eblake@redhat.com>
> > ---
> >  util/systemd.c | 1 +
> >  1 file changed, 1 insertion(+)
> 
> Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>

Thanks; queued on my NBD tree for a pull request this week.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org