man: document that env vars are not suitable for passing secrets

Prompted by the thread around:

https://lists.freedesktop.org/archives/systemd-devel/2018-November/041665.html
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Lennart Poettering 2018-11-13 23:09:32 +01:00 committed by Evgeny Vereshchagin
parent 06bd149a71
commit 438311a518

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@ -1645,7 +1645,13 @@ SystemCallErrorNumber=EPERM</programlisting>
<para> <para>
See <citerefentry See <citerefentry
project='man-pages'><refentrytitle>environ</refentrytitle><manvolnum>7</manvolnum></citerefentry> for details project='man-pages'><refentrytitle>environ</refentrytitle><manvolnum>7</manvolnum></citerefentry> for details
about environment variables.</para></listitem> about environment variables.</para>
<para>Note that environment variables are not suitable for passing secrets (such as passwords, key material, …)
to service processes. Environment variables set for a unit are exposed to unprivileged clients via D-Bus IPC,
and generally not understood as being data that requires protection. Moreover, environment variables are
propagated down the process tree, including across security boundaries (such as setuid/setgid executables), and
hence might leak to processes that should not have access to the secret data.</para></listitem>
</varlistentry> </varlistentry>
<varlistentry> <varlistentry>