network/dhcp-server: improvements for saving/loading leases (#37835)

NEWS

@@ -398,6 +398,10 @@ CHANGES WITH 258 in spe:
           networkd.conf. (Previously this had to be configured individually in
           each .network file.)
 
+        * PersistLeases= setting in [DHCPServer] section now also accepts
+          "runtime", to make the DHCP server saves and loads bound leases on
+          the runtime storage.
+
         * A new Preference= setting has been added to the [IPv6RoutePrefix]
           section to configure the route preference field.
 

man/networkd.conf.xml

@@ -404,7 +404,7 @@ DUIDRawData=00:00:ab:11:f9:2a:c2:77:29:f9:5c:00</programlisting>
         <term><varname>PersistLeases=</varname></term>
         <listitem>
           <para>Specifies the default value for per-network <varname>PersistLeases=</varname>.
-          Takes a boolean. See for details in
+          Takes a boolean or special value <literal>runtime</literal>. See for details in
           <citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
           Defaults to <literal>yes</literal>.</para>
 

man/systemd.network.xml

@@ -443,7 +443,7 @@
 
           <para>Even if this is enabled, the DHCP server will not be started automatically and wait for the
           persistent storage being ready to load/save leases in the storage, unless
-          <varname>RelayTarget=</varname> or <varname>PersistLeases=no</varname> are specified in the
+          <varname>RelayTarget=</varname> or <varname>PersistLeases=no/runtime</varname> are specified in the
           [DHCPServer] section. It will be started after
           <filename>systemd-networkd-persistent-storage.service</filename> is started, which calls
           <command>networkctl persistent-storage yes</command>. See
@@ -4140,16 +4140,24 @@ ServerAddress=192.168.0.1/24</programlisting>
       <varlistentry>
         <term><varname>PersistLeases=</varname></term>
         <listitem>
-          <para>Takes a boolean. When true, the DHCP server will load and save leases in the persistent
-          storage. When false, the DHCP server will neither load nor save leases in the persistent storage.
-          Hence, bound leases will be lost when the interface is reconfigured e.g. by
+          <para>Takes a boolean or special value <literal>runtime</literal>. When <literal>yes</literal>, the
+          DHCP server will load and save leases in the persistent storage. When <literal>runtime</literal>,
+          the DHCP server will load and save leases in the runtime storage, hence bound leases will be lost
+          when the runtime storage is cleared by e.g. by calling
+          <command>systemctl clean systemd-networkd.service</command> or the system is rebooted. When
+          <literal>no</literal>, the DHCP server will neither load nor save leases in the persistent storage,
+          hence bound leases will be lost when the interface is reconfigured e.g. by
           <command>networkctl reconfigure</command>, or
           <citerefentry><refentrytitle>systemd-networkd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
-          is restarted. That may cause address conflict on the network. So, please take an extra care when
-          disable this setting. When unspecified, the value specified in the same setting in
+          is restarted. Using <literal>runtime</literal> and <literal>no</literal> may cause address conflict
+          on the network after the leases are lost. So, please take an extra care when disable this setting.
+          When unspecified, the value specified in the same setting in
           <citerefentry><refentrytitle>networkd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
           which defaults to <literal>yes</literal>, will be used.</para>
 
+          <para>When <varname>RelayTarget=</varname> is specified, this setting will be ignored and no leases
+          will be saved, as there will be no bound lease on the server.</para>
+
           <xi:include href="version-info.xml" xpointer="v256"/>
         </listitem>
       </varlistentry>

network/80-container-ve.network

@@ -29,4 +29,4 @@ IPv6AcceptRA=no
 IPv6SendRA=yes
 
 [DHCPServer]
-PersistLeases=no
+PersistLeases=runtime

network/80-container-vz.network

@@ -28,4 +28,4 @@ IPv6AcceptRA=no
 IPv6SendRA=yes
 
 [DHCPServer]
-PersistLeases=no
+PersistLeases=runtime

network/80-namespace-ns-tun.network

@@ -29,4 +29,4 @@ IPv6AcceptRA=no
 IPv6SendRA=yes
 
 [DHCPServer]
-PersistLeases=no
+PersistLeases=runtime

network/80-namespace-ns.network

@@ -29,4 +29,4 @@ IPv6AcceptRA=no
 IPv6SendRA=yes
 
 [DHCPServer]
-PersistLeases=no
+PersistLeases=runtime

network/80-vm-vt.network

@@ -28,4 +28,4 @@ IPv6AcceptRA=no
 IPv6SendRA=yes
 
 [DHCPServer]
-PersistLeases=no
+PersistLeases=runtime

src/libsystemd-network/sd-dhcp-server.c

@@ -1605,9 +1605,13 @@ int sd_dhcp_server_set_lease_file(sd_dhcp_server *server, int dir_fd, const char
         if (!path_is_safe(path))
                 return -EINVAL;
 
-        _cleanup_close_ int fd = fd_reopen(dir_fd, O_CLOEXEC | O_DIRECTORY | O_PATH);
+        _cleanup_close_ int fd = AT_FDCWD; /* Unlike our usual coding style, AT_FDCWD needs to be set,
+                                            * to pass a 'valid' fd. */
+        if (dir_fd >= 0) {
+                fd = fd_reopen(dir_fd, O_CLOEXEC | O_DIRECTORY | O_PATH);
                 if (fd < 0)
                         return fd;
+        }
 
         r = free_and_strdup(&server->lease_file, path);
         if (r < 0)

src/network/networkd-dhcp-server.c

@@ -27,6 +27,7 @@
 #include "path-util.h"
 #include "set.h"
 #include "socket-netlink.h"
+#include "string-table.h"
 #include "string-util.h"
 #include "strv.h"
 
@@ -150,13 +151,13 @@ int network_adjust_dhcp_server(Network *network, Set **addresses) {
         return 0;
 }
 
-static bool dhcp_server_persist_leases(Link *link) {
+static DHCPServerPersistLeases link_get_dhcp_server_persist_leases(Link *link) {
         assert(link);
         assert(link->manager);
         assert(link->network);
 
         if (in4_addr_is_set(&link->network->dhcp_server_relay_target))
-                return false; /* On relay mode. Nothing saved in the persistent storage. */
+                return DHCP_SERVER_PERSIST_LEASES_NO; /* On relay mode. Nothing saved in the persistent storage. */
 
         if (link->network->dhcp_server_persist_leases >= 0)
                 return link->network->dhcp_server_persist_leases;
@@ -164,9 +165,47 @@ static bool dhcp_server_persist_leases(Link *link) {
         return link->manager->dhcp_server_persist_leases;
 }
 
+static int link_get_dhcp_server_lease_file(Link *link, int *ret_dir_fd, char **ret_path) {
+        assert(link);
+        assert(link->ifname);
+        assert(ret_dir_fd);
+        assert(ret_path);
+
+        /* This does not copy fd. Do not close fd stored in ret_dir_fd. */
+
+        switch (link_get_dhcp_server_persist_leases(link)) {
+        case DHCP_SERVER_PERSIST_LEASES_NO:
+                *ret_dir_fd = -EBADF;
+                *ret_path = NULL;
+                return 0;
+
+        case DHCP_SERVER_PERSIST_LEASES_YES: {
+                if (link->manager->persistent_storage_fd < 0)
+                        return -EBUSY; /* persistent storage is not ready. */
+
+                char *p = path_join("dhcp-server-lease", link->ifname);
+                if (!p)
+                        return -ENOMEM;
+
+                *ret_dir_fd = link->manager->persistent_storage_fd;
+                *ret_path = p;
+                return 1;
+        }
+        case DHCP_SERVER_PERSIST_LEASES_RUNTIME: {
+                char *p = path_join("/run/systemd/netif/dhcp-server-lease", link->ifname);
+                if (!p)
+                        return -ENOMEM;
+
+                *ret_dir_fd = AT_FDCWD;
+                *ret_path = p;
+                return 1;
+        }
+        default:
+                assert_not_reached();
+        }
+}
+
 int address_acquire_from_dhcp_server_leases_file(Link *link, const Address *address, union in_addr_union *ret) {
-        struct in_addr a;
-        uint8_t prefixlen;
         int r;
 
         assert(link);
@@ -185,18 +224,18 @@ int address_acquire_from_dhcp_server_leases_file(Link *link, const Address *addr
         if (!link_dhcp4_server_enabled(link))
                 return -ENOENT;
 
-        if (!dhcp_server_persist_leases(link))
+        _cleanup_free_ char *lease_file = NULL;
+        int dir_fd;
+        r = link_get_dhcp_server_lease_file(link, &dir_fd, &lease_file);
+        if (r < 0)
+                return r;
+        if (r == 0) /* persistent leases is disabled */
                 return -ENOENT;
 
-        if (link->manager->persistent_storage_fd < 0)
-                return -EBUSY; /* The persistent storage is not ready, try later again. */
-
-        _cleanup_free_ char *lease_file = path_join("dhcp-server-lease", link->ifname);
-        if (!lease_file)
-                return -ENOMEM;
-
+        struct in_addr a;
+        uint8_t prefixlen;
         r = dhcp_server_leases_file_get_server_address(
-                        link->manager->persistent_storage_fd,
+                        dir_fd,
                         lease_file,
                         &a,
                         &prefixlen);
@@ -234,16 +273,15 @@ int link_start_dhcp4_server(Link *link) {
         /* TODO: Maybe, also check the system time is synced. If the system does not have RTC battery, then
          * the realtime clock in not usable in the early boot stage, and all saved leases may be wrongly
          * handled as expired and dropped. */
-        if (dhcp_server_persist_leases(link)) {
-
-                if (link->manager->persistent_storage_fd < 0)
+        _cleanup_free_ char *lease_file = NULL;
+        int dir_fd;
+        r = link_get_dhcp_server_lease_file(link, &dir_fd, &lease_file);
+        if (r == -EBUSY)
                 return 0; /* persistent storage is not ready. */
-
-                _cleanup_free_ char *lease_file = path_join("dhcp-server-lease", link->ifname);
-                if (!lease_file)
-                        return -ENOMEM;
-
-                r = sd_dhcp_server_set_lease_file(link->dhcp_server, link->manager->persistent_storage_fd, lease_file);
+        if (r < 0)
+                return r;
+        if (r > 0) {
+                r = sd_dhcp_server_set_lease_file(link->dhcp_server, dir_fd, lease_file);
                 if (r < 0)
                         return r;
         }
@@ -265,7 +303,7 @@ void manager_toggle_dhcp4_server_state(Manager *manager, bool start) {
         HASHMAP_FOREACH(link, manager->links_by_index) {
                 if (!link->dhcp_server)
                         continue;
-                if (!dhcp_server_persist_leases(link))
+                if (link_get_dhcp_server_persist_leases(link) != DHCP_SERVER_PERSIST_LEASES_YES)
                         continue;
 
                 /* Even if 'start' is true, first we need to stop the server. Otherwise, we cannot (re)set
@@ -916,3 +954,19 @@ int config_parse_dhcp_server_ipv6_only_preferred(
         *usec = t;
         return 0;
 }
+
+static const char* const dhcp_server_persist_leases_table[_DHCP_SERVER_PERSIST_LEASES_MAX] = {
+        [DHCP_SERVER_PERSIST_LEASES_NO]      = "no",
+        [DHCP_SERVER_PERSIST_LEASES_YES]     = "yes",
+        [DHCP_SERVER_PERSIST_LEASES_RUNTIME] = "runtime",
+};
+
+DEFINE_PRIVATE_STRING_TABLE_LOOKUP_FROM_STRING_WITH_BOOLEAN(
+                dhcp_server_persist_leases,
+                DHCPServerPersistLeases,
+                DHCP_SERVER_PERSIST_LEASES_YES);
+
+DEFINE_CONFIG_PARSE_ENUM(
+                config_parse_dhcp_server_persist_leases,
+                dhcp_server_persist_leases,
+                DHCPServerPersistLeases);

src/network/networkd-dhcp-server.h

@@ -3,6 +3,14 @@
 
 #include "networkd-forward.h"
 
+typedef enum DHCPServerPersistLeases {
+        DHCP_SERVER_PERSIST_LEASES_NO,
+        DHCP_SERVER_PERSIST_LEASES_YES,
+        DHCP_SERVER_PERSIST_LEASES_RUNTIME,
+        _DHCP_SERVER_PERSIST_LEASES_MAX,
+        _DHCP_SERVER_PERSIST_LEASES_INVALID = -EINVAL,
+} DHCPServerPersistLeases;
+
 int network_adjust_dhcp_server(Network *network, Set **addresses);
 int address_acquire_from_dhcp_server_leases_file(Link *link, const Address *address, union in_addr_union *ret);
 int link_request_dhcp_server(Link *link);
@@ -14,3 +22,4 @@ CONFIG_PARSER_PROTOTYPE(config_parse_dhcp_server_relay_agent_suboption);
 CONFIG_PARSER_PROTOTYPE(config_parse_dhcp_server_emit);
 CONFIG_PARSER_PROTOTYPE(config_parse_dhcp_server_address);
 CONFIG_PARSER_PROTOTYPE(config_parse_dhcp_server_ipv6_only_preferred);
+CONFIG_PARSER_PROTOTYPE(config_parse_dhcp_server_persist_leases);

src/network/networkd-gperf.gperf

@@ -44,7 +44,7 @@ DHCPv4.DUIDRawData,                      config_parse_duid_rawdata,
 DHCPv6.UseDomains,                       config_parse_use_domains,                0,                                                         offsetof(Manager, dhcp6_use_domains)
 DHCPv6.DUIDType,                         config_parse_duid_type,                  0,                                                         offsetof(Manager, dhcp6_duid)
 DHCPv6.DUIDRawData,                      config_parse_duid_rawdata,               0,                                                         offsetof(Manager, dhcp6_duid)
-DHCPServer.PersistLeases,                config_parse_bool,                       0,                                                         offsetof(Manager, dhcp_server_persist_leases)
+DHCPServer.PersistLeases,                config_parse_dhcp_server_persist_leases, 0,                                                         offsetof(Manager, dhcp_server_persist_leases)
 /* Deprecated */
 DHCP.DUIDType,                           config_parse_manager_duid_type,          0,                                                         0
 DHCP.DUIDRawData,                        config_parse_manager_duid_rawdata,       0,                                                         0

src/network/networkd-manager.c

@@ -635,7 +635,7 @@ int manager_new(Manager **ret, bool test_mode) {
                 .dhcp_duid.type = DUID_TYPE_EN,
                 .dhcp6_duid.type = DUID_TYPE_EN,
                 .duid_product_uuid.type = DUID_TYPE_UUID,
-                .dhcp_server_persist_leases = true,
+                .dhcp_server_persist_leases = DHCP_SERVER_PERSIST_LEASES_YES,
                 .serialization_fd = -EBADF,
                 .ip_forwarding = { -1, -1, },
 #if HAVE_VMLINUX_H

src/network/networkd-manager.h

@@ -36,7 +36,7 @@ typedef struct Manager {
         bool manage_foreign_routes;
         bool manage_foreign_rules;
         bool manage_foreign_nexthops;
-        bool dhcp_server_persist_leases;
+        DHCPServerPersistLeases dhcp_server_persist_leases;
 
         Set *dirty_links;
         Set *new_wlan_ifindices;

src/network/networkd-network-gperf.gperf

@@ -389,7 +389,7 @@ DHCPServer.BootServerAddress,                config_parse_in_addr_non_null,
 DHCPServer.BootServerName,                   config_parse_dns_name,                                    0,                             offsetof(Network, dhcp_server_boot_server_name)
 DHCPServer.BootFilename,                     config_parse_string,                                      CONFIG_PARSE_STRING_SAFE_AND_ASCII, offsetof(Network, dhcp_server_boot_filename)
 DHCPServer.RapidCommit,                      config_parse_bool,                                        0,                             offsetof(Network, dhcp_server_rapid_commit)
-DHCPServer.PersistLeases,                    config_parse_tristate,                                    0,                             offsetof(Network, dhcp_server_persist_leases)
+DHCPServer.PersistLeases,                    config_parse_dhcp_server_persist_leases,                  0,                             offsetof(Network, dhcp_server_persist_leases)
 DHCPServerStaticLease.Address,               config_parse_dhcp_static_lease_address,                   0,                             0
 DHCPServerStaticLease.MACAddress,            config_parse_dhcp_static_lease_hwaddr,                    0,                             0
 Bridge.Cost,                                 config_parse_uint32,                                      0,                             offsetof(Network, cost)

src/network/networkd-network.c

@@ -435,7 +435,7 @@ int network_load_one(Manager *manager, OrderedHashmap **networks, const char *fi
                 .dhcp_server_emit_router = true,
                 .dhcp_server_emit_timezone = true,
                 .dhcp_server_rapid_commit = true,
-                .dhcp_server_persist_leases = -1,
+                .dhcp_server_persist_leases = _DHCP_SERVER_PERSIST_LEASES_INVALID,
 
                 .router_lifetime_usec = RADV_DEFAULT_ROUTER_LIFETIME_USEC,
                 .router_dns_lifetime_usec = RADV_DEFAULT_VALID_LIFETIME_USEC,

src/network/networkd-network.h

@@ -11,6 +11,7 @@
 #include "network-util.h"
 #include "networkd-bridge-vlan.h"
 #include "networkd-dhcp-common.h"
+#include "networkd-dhcp-server.h"
 #include "networkd-dhcp4.h"
 #include "networkd-dhcp6.h"
 #include "networkd-dns.h"
@@ -228,7 +229,7 @@ typedef struct Network {
         char *dhcp_server_boot_filename;
         usec_t dhcp_server_ipv6_only_preferred_usec;
         bool dhcp_server_rapid_commit;
-        int dhcp_server_persist_leases;
+        DHCPServerPersistLeases dhcp_server_persist_leases;
 
         /* link-local addressing support */
         AddressFamily link_local;

src/network/networkd.c

@@ -69,8 +69,9 @@ static int run(int argc, char *argv[]) {
         /* Always create the directories people can create inotify watches in. It is necessary to create the
          * following subdirectories after drop_privileges() to make them owned by systemd-network. */
         FOREACH_STRING(p,
-                       "/run/systemd/netif/links/",
-                       "/run/systemd/netif/leases/") {
+                       "/run/systemd/netif/dhcp-server-lease/",
+                       "/run/systemd/netif/leases/",
+                       "/run/systemd/netif/links/") {
                 r = mkdir_safe_label(p, 0755, UID_INVALID, GID_INVALID, MKDIR_WARN_MODE);
                 if (r < 0)
                         log_warning_errno(r, "Could not create directory '%s': %m", p);

test/test-network/conf/persist-leases-runtime.conf

@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: LGPL-2.1-or-later
+[DHCPServer]
+PersistLeases=runtime

test/test-network/systemd-networkd-tests.py

@@ -7110,7 +7110,7 @@ class NetworkdDHCPServerTests(unittest.TestCase, Utilities):
     def tearDown(self):
         tear_down_common()
 
-    def check_dhcp_server(self, persist_leases=True):
+    def check_dhcp_server(self, persist_leases='yes'):
         output = networkctl_status('veth99')
         print(output)
         self.assertRegex(output, r'Address: 192.168.5.[0-9]* \(DHCPv4 via 192.168.5.1\)')
@@ -7122,11 +7122,16 @@ class NetworkdDHCPServerTests(unittest.TestCase, Utilities):
         print(output)
         self.assertRegex(output, "Offered DHCP leases: 192.168.5.[0-9]*")
 
-        if persist_leases:
-            with open('/var/lib/systemd/network/dhcp-server-lease/veth-peer', encoding='utf-8') as f:
-                check_json(f.read())
+        if persist_leases == 'yes':
+            path = '/var/lib/systemd/network/dhcp-server-lease/veth-peer'
+        elif persist_leases == 'runtime':
+            path = '/run/systemd/netif/dhcp-server-lease/veth-peer'
         else:
-            self.assertFalse(os.path.exists('/var/lib/systemd/network/dhcp-server-lease/veth-peer'))
+            path = None
+
+        if path:
+            with open(path, encoding='utf-8') as f:
+                check_json(f.read())
 
     def test_dhcp_server(self):
         copy_network_unit('25-veth.netdev', '25-dhcp-client.network', '25-dhcp-server.network')
@@ -7152,7 +7157,7 @@ class NetworkdDHCPServerTests(unittest.TestCase, Utilities):
         start_networkd()
         self.wait_online('veth99:routable', 'veth-peer:routable')
 
-        self.check_dhcp_server(persist_leases=False)
+        self.check_dhcp_server(persist_leases='no')
 
         remove_networkd_conf_dropin('persist-leases-no.conf')
         with open(os.path.join(network_unit_dir, '25-dhcp-server.network'), mode='a', encoding='utf-8') as f:
@@ -7160,7 +7165,23 @@ class NetworkdDHCPServerTests(unittest.TestCase, Utilities):
         restart_networkd()
         self.wait_online('veth99:routable', 'veth-peer:routable')
 
-        self.check_dhcp_server(persist_leases=False)
+        self.check_dhcp_server(persist_leases='no')
+
+    def test_dhcp_server_persist_leases_runtime(self):
+        copy_networkd_conf_dropin('persist-leases-runtime.conf')
+        copy_network_unit('25-veth.netdev', '25-dhcp-client.network', '25-dhcp-server.network')
+        start_networkd()
+        self.wait_online('veth99:routable', 'veth-peer:routable')
+
+        self.check_dhcp_server(persist_leases='runtime')
+
+        remove_networkd_conf_dropin('persist-leases-runtime.conf')
+        with open(os.path.join(network_unit_dir, '25-dhcp-server.network'), mode='a', encoding='utf-8') as f:
+            f.write('[DHCPServer]\nPersistLeases=runtime')
+        restart_networkd()
+        self.wait_online('veth99:routable', 'veth-peer:routable')
+
+        self.check_dhcp_server(persist_leases='runtime')
 
     def test_dhcp_server_null_server_address(self):
         copy_network_unit('25-veth.netdev', '25-dhcp-client.network', '25-dhcp-server-null-server-address.network')