network: introduce new UseAddress= setting in [DHCPv6] section

If it is disabled, then the addresses provided by the DHCPv6 server will
be ignored.

Closes #18203.

man/systemd.network.xml

@@ -1866,6 +1866,14 @@ IPv6Token=prefixstable:2002:da8:1::</programlisting></para>
       <varname>DHCP=</varname> setting described above, or invoked by the IPv6 Router Advertisement:</para>
 
       <variablelist class='network-directives'>
+        <varlistentry>
+          <term><varname>UseAddress=</varname></term>
+          <listitem>
+            <para>When true (the default), the IP addresses provided by the DHCPv6 server will be
+            assigned.</para>
+          </listitem>
+        </varlistentry>
+
         <varlistentry>
           <term><varname>UseDNS=</varname></term>
           <term><varname>UseNTP=</varname></term>

src/network/networkd-dhcp6.c

@@ -1078,8 +1078,12 @@ static int dhcp6_address_acquired(Link *link) {
         int r;
 
         assert(link);
+        assert(link->network);
         assert(link->dhcp6_lease);
 
+        if (!link->network->dhcp6_use_address)
+                return 0;
+
         for (sd_dhcp6_lease_reset_address_iter(link->dhcp6_lease);;) {
                 uint32_t lifetime_preferred, lifetime_valid;
                 struct in6_addr ip6_addr;

src/network/networkd-network-gperf.gperf

@@ -221,6 +221,7 @@ DHCPv4.SendOption,                           config_parse_dhcp_send_option,
 DHCPv4.SendVendorOption,                     config_parse_dhcp_send_option,                            0,                             offsetof(Network, dhcp_client_send_vendor_options)
 DHCPv4.RouteMTUBytes,                        config_parse_mtu,                                         AF_INET,                       offsetof(Network, dhcp_route_mtu)
 DHCPv4.FallbackLeaseLifetimeSec,             config_parse_dhcp_fallback_lease_lifetime,                0,                             0
+DHCPv6.UseAddress,                           config_parse_bool,                                        0,                             offsetof(Network, dhcp6_use_address)
 DHCPv6.UseDNS,                               config_parse_dhcp_use_dns,                                0,                             0
 DHCPv6.UseNTP,                               config_parse_dhcp_use_ntp,                                0,                             0
 DHCPv6.RapidCommit,                          config_parse_bool,                                        0,                             offsetof(Network, dhcp6_rapid_commit)

src/network/networkd-network.c

@@ -352,10 +352,11 @@ int network_load_one(Manager *manager, OrderedHashmap **networks, const char *fi
                 .dhcp_use_timezone = false,
                 .dhcp_ip_service_type = -1,
 
+                .dhcp6_use_address = true,
+                .dhcp6_use_dns = true,
+                .dhcp6_use_ntp = true,
                 .dhcp6_rapid_commit = true,
                 .dhcp6_route_metric = DHCP_ROUTE_METRIC,
-                .dhcp6_use_ntp = true,
-                .dhcp6_use_dns = true,
 
                 .dhcp6_pd = -1,
                 .dhcp6_pd_announce = true,

src/network/networkd-network.h

@@ -146,6 +146,7 @@ struct Network {
         OrderedHashmap *dhcp_client_send_vendor_options;
 
         /* DHCPv6 Client support*/
+        bool dhcp6_use_address;
         bool dhcp6_use_dns;
         bool dhcp6_use_dns_set;
         bool dhcp6_use_ntp;

test/fuzz/fuzz-network-parser/directives.network

@@ -125,6 +125,7 @@ MUDURL=
 RouteMTUBytes=
 FallbackLeaseLifetimeSec=
 [DHCPv6]
+UseAddress=
 UseNTP=
 UseDNS=
 RapidCommit=