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sd-varlink: optionally handle SIGTERM/SIGINT explicitly in simple varlink event loop

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This commit is contained in:
Lennart Poettering
2025-09-15 18:17:59 +02:00
parent 04e2cb8928
commit cba8c099a9
4 changed files with 163 additions and 1 deletions
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1
man/rules/meson.build
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@@ -916,6 +916,7 @@ manpages = [
'HAVE_PAM'],
['sd_varlink_push_fd', '3', ['sd_varlink_push_dup_fd'], ''],
['sd_varlink_send', '3', ['sd_varlink_sendb', 'sd_varlink_sendbo'], ''],
['sd_varlink_server_new', '3', [], ''],
['sd_varlink_set_description', '3', ['sd_varlink_get_description'], ''],
['sd_varlink_set_relative_timeout', '3', [], ''],
['sd_watchdog_enabled', '3', [], ''],

145
man/sd_varlink_server_new.xml Normal file
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@@ -0,0 +1,145 @@
<?xml version='1.0'?>
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
<refentry id="sd_varlink_server_new" xmlns:xi="http://www.w3.org/2001/XInclude">
<refentryinfo>
<title>sd_varlink_server_new</title>
<productname>systemd</productname>
</refentryinfo>
<refmeta>
<refentrytitle>sd_varlink_server_new</refentrytitle>
<manvolnum>3</manvolnum>
</refmeta>
<refnamediv>
<refname>sd_varlink_server_new</refname>
<refpurpose>Allocate Varlink server object</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcsynopsisinfo>#include &lt;systemd/sd-varlink.h&gt;</funcsynopsisinfo>
<funcprototype>
<funcdef>int <function>sd_varlink_server_new</function></funcdef>
<paramdef>sd_varlink_server** <parameter>ret</parameter></paramdef>
<paramdef>sd_varlink_server_flags_t <parameter>flags</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para><function>sd_varlink_server_new()</function> allocates a new Varlink server object. Initially the
server does not listen on any socket or file descriptor. The newly allocated server object is returned in
the <parameter>ret</parameter> parameter. Use <function>sd_varlink_server_unref()</function> to release
the server object again after use.</para>
<para>The following flags may be passed in the <parameter>flags</parameter> parameter:</para>
<itemizedlist>
<listitem><para><constant>SD_VARLINK_SERVER_ROOT_ONLY</constant>: only allow connections from UID 0
(i.e. the root user). This has two effects: any incoming connections is authenticated via
<constant>SO_PEERCRED</constant> ensuring the UID reported by the kernel is zero. If this check fails
the connection is immediately terminated. Moreover, when binding a socket inode in the file system, the
access mode is set to 0600 (rather than 0666). If this option is used connections on
non-<constant>AF_UNIX</constant> sockets or via pipes are never permitted.</para></listitem>
<listitem><para><constant>SD_VARLINK_SERVER_MYSELF_ONLY</constant>: this is very similar to
<constant>SD_VARLINK_SERVER_ROOT_ONLY</constant> but enforces that the connecting client's UID must
match the server's UID (i.e. the UID this function is invoked as). For servers that run as UID 0 the
flags are equivalent. If both flags are specified in combination, connections are allowed by both UID 0
and the server's own UID.</para></listitem>
<listitem><para><constant>SD_VARLINK_SERVER_ACCOUNT_UID</constant>: if set connection accounting per
client UID is enabled, and a limit on concurrent connections from the same UID is enforced. The limit can
be set via <function>sd_varlink_server_set_connections_per_uid_max()</function>, and defaults to 3/4th
of the total concurrent connection limit, as settable via
<function>sd_varlink_server_set_connections_max()</function>.</para></listitem>
<listitem><para><constant>SD_VARLINK_SERVER_INHERIT_USERDATA</constant>: if set the user data field for
incoming connection (i.e. <type>sd_varlink</type>) objects (as settable via
<function>sd_varlink_set_userdata()</function>) is automatically set to the userdata field of the
server (i.e. <type>sd_varlink_server</type>) object (as settable via
<function>sd_varlink_server_set_userdata()</function>). If this flag is not specified the connection's
user data field will default to <constant>NULL</constant>.</para></listitem>
<listitem><para><constant>SD_VARLINK_SERVER_INPUT_SENSITIVE</constant>: mark all incoming method call
parameters as security sensitive (equivalent to calling
<function>sd_json_variant_sensitive()</function>). This is useful for services that deal with secrets
and similar, as it ensures that the parameters are kept out of debug logging, and memory used by the
parameters is erased after use.</para></listitem>
<listitem><para><constant>SD_VARLINK_SERVER_ALLOW_FD_PASSING_INPUT</constant>: if set, allow receiving
UNIX file descriptors via the connections, equivalent to calling
<function>sd_varlink_set_allow_fd_passing_input()</function> immediately for each incoming
connection. Note that this only has an effect if <constant>AF_UNIX</constant> sockets are used for
communication.</para></listitem>
<listitem><para><constant>SD_VARLINK_SERVER_ALLOW_FD_PASSING_OUTPUT</constant>: similar, but controls
sending of UNIX file descriptors.</para></listitem>
<listitem><para><constant>SD_VARLINK_SERVER_FD_PASSING_INPUT_STRICT</constant>: this flag can be used
in conjunction with <constant>SD_VARLINK_SERVER_ALLOW_FD_PASSING_INPUT</constant>. If so, file
descriptor passing is turned off on the listening sockets already, ensuring that the connection sockets
derived from it at no time have file descriptor passing enabled. If
<constant>SD_VARLINK_SERVER_ALLOW_FD_PASSING_INPUT</constant> is used without
<constant>SD_VARLINK_SERVER_FD_PASSING_INPUT_STRICT</constant> then a choice when to prohibit or allow
file descriptor passing can still be made after the connection came in, however permitting a time
window where file descriptors might already be enqueued, that then need to be dropped
again.</para></listitem>
<listitem><para><constant>SD_VARLINK_SERVER_HANDLE_SIGINT</constant>: if set, and
<function>sd_varlink_server_loop_auto()</function> is used, incoming <constant>SIGINT</constant>
process signals will be caught gracefully and cause the event loop to exit cleanly.</para></listitem>
<listitem><para><constant>SD_VARLINK_SERVER_HANDLE_SIGTERM</constant>: similar, but does the same for
<constant>SIGTERM</constant>.</para></listitem>
</itemizedlist>
</refsect1>
<refsect1>
<title>Return Value</title>
<para>On success, <function>sd_varlink_server_new()</function> returns a non-negative integer. On
failure, it returns a negative errno-style error code.</para>
<refsect2>
<title>Errors</title>
<para>Returned errors may indicate the following problems:</para>
<variablelist>
<varlistentry>
<term><constant>-EINVAL</constant></term>
<listitem><para>An argument is invalid.</para></listitem>
</varlistentry>
</variablelist>
</refsect2>
</refsect1>
<xi:include href="libsystemd-pkgconfig.xml" />
<refsect1>
<title>History</title>
<para><function>sd_varlink_server_new()</function> was added in version 257.</para>
</refsect1>
<refsect1>
<title>See Also</title>
<para><simplelist type="inline">
<member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
<member><citerefentry><refentrytitle>sd-varlink</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
</simplelist></para>
</refsect1>
</refentry>

16
src/libsystemd/sd-varlink/sd-varlink.c
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@@ -3309,7 +3309,9 @@ _public_ int sd_varlink_server_new(sd_varlink_server **ret, sd_varlink_server_fl
SD_VARLINK_SERVER_INPUT_SENSITIVE|
SD_VARLINK_SERVER_ALLOW_FD_PASSING_INPUT|
SD_VARLINK_SERVER_ALLOW_FD_PASSING_OUTPUT|
SD_VARLINK_SERVER_FD_PASSING_INPUT_STRICT)) == 0, -EINVAL);
SD_VARLINK_SERVER_FD_PASSING_INPUT_STRICT|
SD_VARLINK_SERVER_HANDLE_SIGINT|
SD_VARLINK_SERVER_HANDLE_SIGTERM)) == 0, -EINVAL);
s = new(sd_varlink_server, 1);
if (!s)
@@ -3882,6 +3884,18 @@ _public_ int sd_varlink_server_loop_auto(sd_varlink_server *server) {
if (r < 0)
return r;
if (FLAGS_SET(server->flags, SD_VARLINK_SERVER_HANDLE_SIGINT)) {
r = sd_event_add_signal(event, /* ret= */ NULL, SIGINT|SD_EVENT_SIGNAL_PROCMASK, /* callback= */ NULL, /* userdata= */ NULL);
if (r < 0)
return r;
}
if (FLAGS_SET(server->flags, SD_VARLINK_SERVER_HANDLE_SIGTERM)) {
r = sd_event_add_signal(event, /* ret= */ NULL, SIGTERM|SD_EVENT_SIGNAL_PROCMASK, /* callback= */ NULL, /* userdata= */ NULL);
if (r < 0)
return r;
}
r = sd_varlink_server_attach_event(server, event, 0);
if (r < 0)
return r;

2
src/systemd/sd-varlink.h
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@@ -69,6 +69,8 @@ __extension__ typedef enum _SD_ENUM_TYPE_S64(sd_varlink_server_flags_t) {
SD_VARLINK_SERVER_ALLOW_FD_PASSING_INPUT = 1 << 5, /* Allow receiving fds over all connections */
SD_VARLINK_SERVER_ALLOW_FD_PASSING_OUTPUT = 1 << 6, /* Allow sending fds over all connections */
SD_VARLINK_SERVER_FD_PASSING_INPUT_STRICT = 1 << 7, /* Reject input messages with fds if fd passing is disabled (needs kernel v6.16+) */
SD_VARLINK_SERVER_HANDLE_SIGINT = 1 << 8, /* Exit cleanly on SIGINT */
SD_VARLINK_SERVER_HANDLE_SIGTERM = 1 << 9, /* Exit cleanly on SIGTERM */
_SD_ENUM_FORCE_S64(SD_VARLINK_SERVER)
} sd_varlink_server_flags_t;