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man: document the new (Load|Set)CredentialEncrypted= settings

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Lennart Poettering 2021-06-23 18:15:02 +02:00
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man/systemd.exec.xml
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@ -2338,7 +2338,8 @@ SystemCallErrorNumber=EPERM</programlisting>
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. Use <varname>LoadCredential=</varname> (see below) to pass data to unit processes
the secret data. Use <varname>LoadCredential=</varname>, <varname>LoadCredentialEncrypted=</varname>
or <varname>SetCredentialEncrypted=</varname> (see below) to pass data to unit processes
securely.</para></listitem>
</varlistentry>
@ -2832,6 +2833,7 @@ StandardInputData=SWNrIHNpdHplIGRhIHVuJyBlc3NlIEtsb3BzLAp1ZmYgZWVtYWwga2xvcHAncy
<varlistentry>
<term><varname>LoadCredential=</varname><replaceable>ID</replaceable><optional>:<replaceable>PATH</replaceable></optional></term>
<term><varname>LoadCredentialEncrypted=</varname><replaceable>ID</replaceable><optional>:<replaceable>PATH</replaceable></optional></term>
<listitem><para>Pass a credential to the unit. Credentials are limited-size binary or textual objects
that may be passed to unit processes. They are primarily used for passing cryptographic keys (both
@ -2860,6 +2862,20 @@ StandardInputData=SWNrIHNpdHplIGRhIHVuJyBlc3NlIEtsb3BzLAp1ZmYgZWVtYWwga2xvcHAncy
from the service manager into a service. This option may be used multiple times, each time defining
an additional credential to pass to the unit.</para>
<para>The <varname>LoadCredentialEncrypted=</varname> setting is identical to
<varname>LoadCredential=</varname>, except that the credential data is decrypted before being passed
on to the executed processes. Specifically, the referenced path should refer to a file or socket with
an encrypted credential, as implemented by
<citerefentry><refentrytitle>systemd-creds</refentrytitle><manvolnum>1</manvolnum></citerefentry>. This
credential is loaded, decrypted and then passed to the application in decrypted plaintext form, in
the same way a regular credential specified via <varname>LoadCredential=</varname> would be. A
credential configured this way may encrypted with a secret key derived from the system's TPM2
security chip, or with a secret key stored in
<filename>/var/lib/systemd/credentials.secret</filename>, or with both. Using encrypted credentials
improves security as credentials are not stored in plaintext and only decrypted into plaintext the
moment a service requiring them is started. Moreover, credentials may be bound to the local hardware
and installations, so that they cannot easily be analyzed offline.</para>
<para>The credential files/IPC sockets must be accessible to the service manager, but don't have to
be directly accessible to the unit's processes: the credential data is read and copied into separate,
read-only copies for the unit that are accessible to appropriately privileged processes. This is
@ -2891,6 +2907,7 @@ StandardInputData=SWNrIHNpdHplIGRhIHVuJyBlc3NlIEtsb3BzLAp1ZmYgZWVtYWwga2xvcHAncy
<varlistentry>
<term><varname>SetCredential=</varname><replaceable>ID</replaceable>:<replaceable>VALUE</replaceable></term>
<term><varname>SetCredentialEncrypted=</varname><replaceable>ID</replaceable>:<replaceable>VALUE</replaceable></term>
<listitem><para>The <varname>SetCredential=</varname> setting is similar to
<varname>LoadCredential=</varname> but accepts a literal value to use as data for the credential,
@ -2901,6 +2918,14 @@ StandardInputData=SWNrIHNpdHplIGRhIHVuJyBlc3NlIEtsb3BzLAp1ZmYgZWVtYWwga2xvcHAncy
C-style escaping (i.e. <literal>\n</literal> to embed a newline, or <literal>\x00</literal> to embed
a <constant>NUL</constant> byte).</para>
<para>The <varname>SetCredentialEncrypted=</varname> setting is identical to
<varname>SetCredential=</varname> but expects an encrypted credential in literal form as value. This
allows embedding confidential credentials securely directly in unit files. Use
<citerefentry><refentrytitle>systemd-creds</refentrytitle><manvolnum>1</manvolnum></citerefentry>'
<option>-p</option> switch to generate suitable <varname>SetCredentialEncrypted=</varname> lines
directly from plaintext credentials. For further details see
<varname>LoadCredentialEncrypted=</varname> above.</para>
<para>If a credential of the same ID is listed in both <varname>LoadCredential=</varname> and
<varname>SetCredential=</varname>, the latter will act as default if the former cannot be
retrieved. In this case not being able to retrieve the credential from the path specified in