services: Support running Exim with setuid/setgid.

In a typical configuration, Exim binary is setuid root and the Exim daemon
process listens for connections under a non-root system account (usually
`exim`).  Upon receiving a message, it forks into a child process which
re-executes the binary to regain privileges and deliver the mail to its
destination (e.g. a Maildir inside user's home directory).

Besides the setuid binary itself, such setup also requires the Exim
configuration file to live at the path Exim considers safe.  It defaults to
/etc/exim.conf and changing it requires rebuilding the Exim daemon.  If a
configuration at unsafe path is used instead, Exim drops its privileges before
reading it and becomes unable to perform certain kinds of email delivery.

* gnu/services/mail.scm (<exim-configuration>)[setuid-user]: New field.
(<exim-configuration>)[setgid-group]: New field.
(exim-computed-config-file): Delete variable.
(exim-shepherd-service)[start]: Use Exim's default config at /etc/exim.conf.
(exim-activation): Atomically put Exim's current config at /etc/exim.conf and
verify its syntactic correctness.
(exim-setuids): New variable.
(exim-service-type)[extensions]: Extend `setuid-program-service-type`.

Change-Id: Ie6153baac80180d3d48f6b5a6959895df06aef0b

0 files changed, 0 insertions, 0 deletions