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resolved: read DNS conf also from creds and kernel cmdline

Browse Source 
Note that this drops ProtectProc=invisible from
systemd-resolved.service.

This is done because othewise access to the booted "kernel" command line is not
necessarily available. That's because in containers we want to read
/proc/1/cmdline for that.

Fixes: #24103
This commit is contained in:
Lennart Poettering 2023-01-05 15:35:20 +01:00
parent ea575e176a
commit 116687f267
5 changed files with 164 additions and 4 deletions
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9
man/kernel-command-line.xml
View File

@ -478,6 +478,15 @@
</listitem>
</varlistentry>
<varlistentry>
<term><varname>nameserver=</varname></term>
<term><varname>domain=</varname></term>
<listitem><para>Configures DNS server information and search domains, see
<citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
for details.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>resume=</varname></term>
<term><varname>resumeflags=</varname></term>

43
man/systemd-resolved.service.xml
View File

@ -399,6 +399,49 @@ search foobar.com barbar.com
</variablelist>
</refsect1>
<refsect1>
<title>Credentials</title>
<para><command>systemd-resolved</command> supports the service credentials logic as implemented by
<varname>LoadCredential=</varname>/<varname>SetCredential=</varname> (see
<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>1</manvolnum></citerefentry> for
details). The following credentials are used when passed in:</para>
<variablelist>
<varlistentry>
<term><varname>network.dns</varname></term>
<term><varname>network.search_domains</varname></term>
<listitem><para>May contain a space separated list of DNS server IP addresses and DNS search
domains. This information is only used when no explicit configuration via
<filename>/etc/systemd/resolved.conf</filename>, <filename>/etc/resolv.conf</filename> or the kernel
command line has been provided.</para></listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Kernel Command Line</title>
<para><command>systemd-resolved</command> also honours two kernel command line options:</para>
<variablelist class='kernel-commandline-options'>
<varlistentry>
<term><varname>nameserver=</varname></term>
<term><varname>domain=</varname></term>
<listitem><para>Takes the IP address of a DNS server (in case of <varname>nameserver=</varname>), and
a DNS search domain (in case of <varname>domain=</varname>). May be used multiple times, to define
multiple DNS servers/search domains. If either of these options are specified
<filename>/etc/resolv.conf</filename> will not be read and the <varname>DNS=</varname> and
<varname>Domains=</varname> settings of
<citerefentry><refentrytitle>resolved.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
will be ignored. These two kernel command line options hence override system
configuration.</para></listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>See Also</title>
<para>

9
man/systemd.system-credentials.xml
View File

@ -115,6 +115,15 @@
</listitem>
</varlistentry>
<varlistentry>
<term><varname>network.dns</varname></term>
<term><varname>network.search_domains</varname></term>
<listitem>
<para>DNS server information and search domains. Read by
<citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>passwd.hashed-password.root</varname></term>
<term><varname>passwd.plaintext-password.root</varname></term>

104
src/resolve/resolved-conf.c
View File

@ -3,15 +3,17 @@
#include "alloc-util.h"
#include "conf-parser.h"
#include "constants.h"
#include "creds-util.h"
#include "dns-domain.h"
#include "extract-word.h"
#include "hexdecoct.h"
#include "parse-util.h"
#include "proc-cmdline.h"
#include "resolved-conf.h"
#include "resolved-dnssd.h"
#include "resolved-manager.h"
#include "resolved-dns-search-domain.h"
#include "resolved-dns-stub.h"
#include "dns-domain.h"
#include "resolved-dnssd.h"
#include "resolved-manager.h"
#include "socket-netlink.h"
#include "specifier.h"
#include "string-table.h"
@ -463,6 +465,99 @@ int config_parse_dns_stub_listener_extra(
return 0;
}
static void read_credentials(Manager *m) {
_cleanup_free_ char *dns = NULL, *domains = NULL;
int r;
assert(m);
/* Hmm, if we aren't supposed to read /etc/resolv.conf because the DNS settings were already
* configured explicitly in our config file, we don't want to honour credentials either */
if (!m->read_resolv_conf)
return;
r = read_credential_strings_many(
"network.dns", &dns,
"network.search_domains", &domains);
if (r < 0 && !IN_SET(r, -ENXIO, -ENOENT))
log_warning_errno(r, "Failed to read credentials, ignoring: %m");
if (dns) {
r = manager_parse_dns_server_string_and_warn(m, DNS_SERVER_SYSTEM, dns);
if (r < 0)
log_warning_errno(r, "Failed to parse credential provided DNS server string '%s', ignoring.", dns);
m->read_resolv_conf = false;
}
if (domains) {
r = manager_parse_search_domains_and_warn(m, domains);
if (r < 0)
log_warning_errno(r, "Failed to parse credential provided search domain string '%s', ignoring.", domains);
m->read_resolv_conf = false;
}
}
struct ProcCmdlineInfo {
Manager *manager;
/* If there's a setting configured via /proc/cmdline we want to reset the configured lists, but only
* once, so that multiple nameserver= or domain= settings can be specified on the kernel command line
* and will be combined. These booleans will be set once we erase the list once. */
bool dns_server_unlinked;
bool search_domain_unlinked;
};
static int proc_cmdline_callback(const char *key, const char *value, void *data) {
struct ProcCmdlineInfo *info = ASSERT_PTR(data);
int r;
assert(info->manager);
/* The kernel command line option names are chosen to be compatible with what various tools already
* interpret, for example dracut and SUSE Linux. */
if (proc_cmdline_key_streq(key, "nameserver")) {
if (!info->dns_server_unlinked) {
/* The kernel command line overrides any prior configuration */
dns_server_unlink_all(manager_get_first_dns_server(info->manager, DNS_SERVER_SYSTEM));
info->dns_server_unlinked = true;
}
r = manager_parse_dns_server_string_and_warn(info->manager, DNS_SERVER_SYSTEM, value);
if (r < 0)
log_warning_errno(r, "Failed to parse DNS server string '%s', ignoring.", value);
info->manager->read_resolv_conf = false;
} else if (proc_cmdline_key_streq(key, "domain")) {
if (!info->search_domain_unlinked) {
dns_search_domain_unlink_all(info->manager->search_domains);
info->search_domain_unlinked = true;
}
r = manager_parse_search_domains_and_warn(info->manager, value);
if (r < 0)
log_warning_errno(r, "Failed to parse credential provided search domain string '%s', ignoring.", value);
info->manager->read_resolv_conf = false;
}
return 0;
}
static void read_proc_cmdline(Manager *m) {
int r;
assert(m);
r = proc_cmdline_parse(proc_cmdline_callback, &(struct ProcCmdlineInfo) { .manager = m }, 0);
if (r < 0)
log_warning_errno(r, "Failed to read kernel command line, ignoring: %m");
}
int manager_parse_config_file(Manager *m) {
int r;
@ -479,6 +574,9 @@ int manager_parse_config_file(Manager *m) {
if (r < 0)
return r;
read_credentials(m); /* credentials are only used when nothing is explicitly configured … */
read_proc_cmdline(m); /* … but kernel command line overrides local configuration. */
if (m->need_builtin_fallbacks) {
r = manager_parse_dns_server_string_and_warn(m, DNS_SERVER_FALLBACK, DNS_SERVERS);
if (r < 0)

3
units/systemd-resolved.service.in
View File

@ -30,7 +30,6 @@ MemoryDenyWriteExecute=yes
NoNewPrivileges=yes
PrivateDevices=yes
PrivateTmp=yes
ProtectProc=invisible
ProtectClock=yes
ProtectControlGroups=yes
ProtectHome=yes
@ -51,6 +50,8 @@ SystemCallErrorNumber=EPERM
SystemCallFilter=@system-service
Type=notify
User=systemd-resolve
LoadCredential=network.dns
LoadCredential=network.search_domains
{{SERVICE_WATCHDOG}}
[Install]