systemd-user: Add service file to create the socketdir
Needs ReviewPublic

Authored by mattst88 on Jun 19 2017, 10:59 PM.

Details

Reviewers
dkg
Summary

When forwarding the GnuPG agent to a remote system running systemd over SSH, the /run/user/$UID/gnupg directory does not exist before SSH attempts to place a socket in it, causing agent forwarding to fail.

This systemd user service runs gpgconf --create-socketdir on login, allowing agent forwarding to work successfully.

Test Plan

Configure a local and remote system for GPG agent forwarding over SSH, as described by https://wiki.gnupg.org/AgentForwarding ; The remote system should be running systemd.

SSH to the remote system and see that remote forwarding fails:

Error: remote port forwarding failed for listen path /run/user/1000/gnupg/S.gpg-agent

This is because /run/user/1000/gnupg does not exist when SSH attempt to place the socket. The suggestion in the documentation to run "gpgconf --create-socketdir" from .bashrc/.zshrc does not work, because those are sourced after SSH attempts to place the socket.

Instead, using the proposed systemd user service to create the directory allows forwarding to work.

Diff Detail

Repository
rG GnuPG
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mattst88 created this revision.Jun 19 2017, 10:59 PM
dkg added a comment.Jun 21 2017, 12:13 AM

aiui, the point here is to have the user "service" get triggered somehow (through pam's pam_systemd.so's session module?) before ssh goes ahead and forms the socket. is that right? If the pre-launch mechanism is pam, is there a reason to do it as a systemd user service? That won't work for systems that have pam but don't have systemd, whereas a pam module that creates these will work.

as i said in the mailing list thread, i think the right place to fix this is in OpenSSH itself -- it should be willing to try to create the leading directories to the socket path if possible when forwarding a socket.

so in order of preference for resolving this, i'm inclined to say:

  • OpenSSH
  • PAM module
  • *maybe* systemd

Even if systemd gets used, i'm not sure this is the right way to do it. if this wasn't a user service, the right mechanism would be tmpfiles.d (systemd-tmpfiles). But i don't know of a typical per-user analog for systemd-tmpfiles, and i'm not sure just running systemd-tmpfiles as a user service will behave the way we'd want it to. In any case, i thnk the unit file proposed here wants at least Type=oneshot and possibly RemainAfterExit=yes. but i don't think this is the right way to solve the underlying problem.