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

[Daniel P . Berrangé]

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>


With regards,
Daniel
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