network: DHCPv6 client add support for prefix delegation hint

Add support for prefix hint lenth and prefix hint address
```
Frame 43: 177 bytes on wire (1416 bits), 177 bytes captured (1416 bits) on interface 0
Ethernet II, Src: f6:c1:08:4d:45:f1 (f6:c1:08:4d:45:f1), Dst: IPv6mcast_01:00:02 (33:33:00:01:00:02)
Internet Protocol Version 6, Src: fe80::d250:c82:7f6e:28d6, Dst: ff02::1:2
User Datagram Protocol, Src Port: 546, Dst Port: 547
DHCPv6
    Message type: Solicit (1)
    Transaction ID: 0x5c7902
    Rapid Commit
    Identity Association for Non-temporary Address
    Fully Qualified Domain Name
    Identity Association for Prefix Delegation
        Option: Identity Association for Prefix Delegation (25)
        Length: 41
        Value: 1b97b1690000000000000000001a0019ffffffffffffffff…
        IAID: 1b97b169
        T1: 0
        T2: 0
        IA Prefix
            Option: IA Prefix (26)
            Length: 25
            Value: ffffffffffffffff3c000000000000000000000000000000…
            Preferred lifetime: infinity
            Valid lifetime: infinity
            Prefix length: 60
            Prefix address: ::
    Option Request
    Client Identifier
    Elapsed time
```

man/systemd.network.xml

@@ -1632,6 +1632,14 @@
           </listitem>
         </varlistentry>
 
+        <varlistentry>
+          <term><varname>PrefixDelegationHint=</varname></term>
+          <listitem>
+            <para>Takes an IPv6 address with prefix length as <varname>Addresss=</varname> in
+            the "[Network]" section. Specifies the DHCPv6 client for the requesting router to include
+            a prefix-hint in the DHCPv6 solicitation. Prefix ranges 1-128. Defaults to unset.</para>
+          </listitem>
+        </varlistentry>
       </variablelist>
   </refsect1>
 

src/libsystemd-network/dhcp6-internal.h

@@ -85,7 +85,7 @@ typedef struct DHCP6IA DHCP6IA;
 int dhcp6_option_append(uint8_t **buf, size_t *buflen, uint16_t code,
                         size_t optlen, const void *optval);
 int dhcp6_option_append_ia(uint8_t **buf, size_t *buflen, const DHCP6IA *ia);
-int dhcp6_option_append_pd(uint8_t *buf, size_t len, const DHCP6IA *pd);
+int dhcp6_option_append_pd(uint8_t *buf, size_t len, const DHCP6IA *pd, DHCP6Address *hint_pd_prefix);
 int dhcp6_option_append_fqdn(uint8_t **buf, size_t *buflen, const char *fqdn);
 int dhcp6_option_parse(uint8_t **buf, size_t *buflen, uint16_t *optcode,
                        size_t *optlen, uint8_t **optvalue);

src/libsystemd-network/dhcp6-option.c

@@ -168,9 +168,10 @@ int dhcp6_option_append_fqdn(uint8_t **buf, size_t *buflen, const char *fqdn) {
         return r;
 }
 
-int dhcp6_option_append_pd(uint8_t *buf, size_t len, const DHCP6IA *pd) {
+int dhcp6_option_append_pd(uint8_t *buf, size_t len, const DHCP6IA *pd, DHCP6Address *hint_pd_prefix) {
         DHCP6Option *option = (DHCP6Option *)buf;
         size_t i = sizeof(*option) + sizeof(pd->ia_pd);
+        DHCP6PDPrefixOption *prefix_opt;
         DHCP6Address *prefix;
 
         assert_return(buf, -EINVAL);
@@ -183,10 +184,7 @@ int dhcp6_option_append_pd(uint8_t *buf, size_t len, const DHCP6IA *pd) {
         option->code = htobe16(SD_DHCP6_OPTION_IA_PD);
 
         memcpy(&option->data, &pd->ia_pd, sizeof(pd->ia_pd));
-
         LIST_FOREACH(addresses, prefix, pd->addresses) {
-                DHCP6PDPrefixOption *prefix_opt;
-
                 if (len < i + sizeof(*prefix_opt))
                         return -ENOBUFS;
 
@@ -194,9 +192,19 @@ int dhcp6_option_append_pd(uint8_t *buf, size_t len, const DHCP6IA *pd) {
                 prefix_opt->option.code = htobe16(SD_DHCP6_OPTION_IA_PD_PREFIX);
                 prefix_opt->option.len = htobe16(sizeof(prefix_opt->iapdprefix));
 
-                memcpy(&prefix_opt->iapdprefix, &prefix->iapdprefix,
-                       sizeof(struct iapdprefix));
+                memcpy(&prefix_opt->iapdprefix, &prefix->iapdprefix, sizeof(struct iapdprefix));
+                i += sizeof(*prefix_opt);
+        }
 
+        if (hint_pd_prefix && hint_pd_prefix->iapdprefix.prefixlen > 0) {
+                if (len < i + sizeof(*prefix_opt))
+                        return -ENOBUFS;
+
+                prefix_opt = (DHCP6PDPrefixOption *)&buf[i];
+                prefix_opt->option.code = htobe16(SD_DHCP6_OPTION_IA_PD_PREFIX);
+                prefix_opt->option.len = htobe16(sizeof(prefix_opt->iapdprefix));
+
+                memcpy(&prefix_opt->iapdprefix, &hint_pd_prefix->iapdprefix, sizeof(struct iapdprefix));
                 i += sizeof(*prefix_opt);
         }
 

src/libsystemd-network/sd-dhcp6-client.c

@@ -46,6 +46,7 @@ struct sd_dhcp6_client {
         sd_event *event;
         int event_priority;
         int ifindex;
+        DHCP6Address hint_pd_prefix;
         struct in6_addr local_address;
         uint8_t mac_addr[MAX_MAC_ADDR_LEN];
         size_t mac_addr_len;
@@ -187,6 +188,22 @@ int sd_dhcp6_client_set_mac(
         return 0;
 }
 
+int sd_dhcp6_client_set_prefix_delegation_hint(
+                sd_dhcp6_client *client,
+                uint8_t prefixlen,
+                const struct in6_addr *pd_address) {
+
+        assert_return(client, -EINVAL);
+        assert_return(pd_address, -EINVAL);
+
+        assert_return(IN_SET(client->state, DHCP6_STATE_STOPPED), -EBUSY);
+
+        client->hint_pd_prefix.iapdprefix.address = *pd_address;
+        client->hint_pd_prefix.iapdprefix.prefixlen = prefixlen;
+
+        return 0;
+}
+
 static int client_ensure_duid(sd_dhcp6_client *client) {
         if (client->duid_len != 0)
                 return 0;
@@ -492,7 +509,7 @@ static int client_send_message(sd_dhcp6_client *client, usec_t time_now) {
                 }
 
                 if (FLAGS_SET(client->request, DHCP6_REQUEST_IA_PD)) {
-                        r = dhcp6_option_append_pd(opt, optlen, &client->ia_pd);
+                        r = dhcp6_option_append_pd(opt, optlen, &client->ia_pd, &client->hint_pd_prefix);
                         if (r < 0)
                                 return r;
 
@@ -530,7 +547,7 @@ static int client_send_message(sd_dhcp6_client *client, usec_t time_now) {
                 }
 
                 if (FLAGS_SET(client->request, DHCP6_REQUEST_IA_PD)) {
-                        r = dhcp6_option_append_pd(opt, optlen, &client->lease->pd);
+                        r = dhcp6_option_append_pd(opt, optlen, &client->lease->pd, NULL);
                         if (r < 0)
                                 return r;
 
@@ -556,7 +573,7 @@ static int client_send_message(sd_dhcp6_client *client, usec_t time_now) {
                 }
 
                 if (FLAGS_SET(client->request, DHCP6_REQUEST_IA_PD)) {
-                        r = dhcp6_option_append_pd(opt, optlen, &client->lease->pd);
+                        r = dhcp6_option_append_pd(opt, optlen, &client->lease->pd, NULL);
                         if (r < 0)
                                 return r;
 
@@ -1537,6 +1554,8 @@ int sd_dhcp6_client_new(sd_dhcp6_client **ret) {
                 .request = DHCP6_REQUEST_IA_NA,
                 .fd = -1,
                 .req_opts_len = ELEMENTSOF(default_req_opts),
+                .hint_pd_prefix.iapdprefix.lifetime_preferred = (be32_t) -1,
+                .hint_pd_prefix.iapdprefix.lifetime_valid = (be32_t) -1,
                 .req_opts = TAKE_PTR(req_opts),
         };
 

src/network/networkd-dhcp-common.c

@@ -1,5 +1,6 @@
 /* SPDX-License-Identifier: LGPL-2.1+ */
 
+#include "in-addr-util.h"
 #include "networkd-dhcp-common.h"
 #include "networkd-network.h"
 #include "parse-util.h"
@@ -227,6 +228,41 @@ int config_parse_iaid(const char *unit,
         return 0;
 }
 
+int config_parse_dhcp6_pd_hint(
+                const char* unit,
+                const char *filename,
+                unsigned line,
+                const char *section,
+                unsigned section_line,
+                const char *lvalue,
+                int ltype,
+                const char *rvalue,
+                void *data,
+                void *userdata) {
+
+        Network *network = data;
+        int r;
+
+        assert(filename);
+        assert(lvalue);
+        assert(rvalue);
+        assert(data);
+
+        r = in_addr_prefix_from_string(rvalue, AF_INET6, (union in_addr_union *) &network->dhcp6_pd_address, &network->dhcp6_pd_length);
+        if (r < 0) {
+                log_syntax(unit, LOG_ERR, filename, line, r, "Failed to parse PrefixDelegationHint=%s, ignoring assignment", rvalue);
+                return 0;
+        }
+
+        if (network->dhcp6_pd_length < 1 || network->dhcp6_pd_length > 128) {
+                log_syntax(unit, LOG_ERR, filename, line, 0, "Invalid prefix length='%d', ignoring assignment", network->dhcp6_pd_length);
+                network->dhcp6_pd_length = 0;
+                return 0;
+        }
+
+        return 0;
+}
+
 DEFINE_CONFIG_PARSE_ENUM(config_parse_dhcp_use_domains, dhcp_use_domains, DHCPUseDomains,
                          "Failed to parse DHCP use domains setting");
 

src/network/networkd-dhcp-common.h

@@ -34,3 +34,4 @@ CONFIG_PARSER_PROTOTYPE(config_parse_dhcp_use_ntp);
 CONFIG_PARSER_PROTOTYPE(config_parse_dhcp_use_sip);
 CONFIG_PARSER_PROTOTYPE(config_parse_iaid);
 CONFIG_PARSER_PROTOTYPE(config_parse_section_route_table);
+CONFIG_PARSER_PROTOTYPE(config_parse_dhcp6_pd_hint);

src/network/networkd-dhcp6.c

@@ -686,6 +686,12 @@ int dhcp6_configure(Link *link) {
                         return log_link_error_errno(link, r, "DHCP6 CLIENT: Failed to set prefix delegation: %m");
         }
 
+        if (link->network->dhcp6_pd_length > 0) {
+                r = sd_dhcp6_client_set_prefix_delegation_hint(client, link->network->dhcp6_pd_length, &link->network->dhcp6_pd_address);
+                if (r < 0)
+                        return log_link_error_errno(link, r, "DHCP6 CLIENT: Failed to set prefix hint: %m");
+        }
+
         link->dhcp6_client = TAKE_PTR(client);
 
         return 0;

src/network/networkd-network-gperf.gperf

@@ -172,6 +172,7 @@ DHCPv6.UseDNS,                          config_parse_bool,
 DHCPv6.UseNTP,                          config_parse_bool,                               0,                             offsetof(Network, dhcp6_use_ntp)
 DHCPv6.RapidCommit,                     config_parse_bool,                               0,                             offsetof(Network, rapid_commit)
 DHCPv6.ForceDHCPv6PDOtherInformation,   config_parse_bool,                               0,                             offsetof(Network, dhcp6_force_pd_other_information)
+DHCPv6.PrefixDelegationHint,            config_parse_dhcp6_pd_hint,                    0,                             0
 IPv6AcceptRA.UseAutonomousPrefix,       config_parse_bool,                               0,                             offsetof(Network, ipv6_accept_ra_use_autonomous_prefix)
 IPv6AcceptRA.UseOnLinkPrefix,           config_parse_bool,                               0,                             offsetof(Network, ipv6_accept_ra_use_onlink_prefix)
 IPv6AcceptRA.UseDNS,                    config_parse_bool,                               0,                             offsetof(Network, ipv6_accept_ra_use_dns)

src/network/networkd-network.h

@@ -109,6 +109,8 @@ struct Network {
         /* DHCPv6 Client support*/
         bool dhcp6_use_dns;
         bool dhcp6_use_ntp;
+        uint8_t dhcp6_pd_length;
+        struct in6_addr dhcp6_pd_address;
 
         /* DHCP Server Support */
         bool dhcp_server;

src/systemd/sd-dhcp6-client.h

@@ -120,6 +120,10 @@ int sd_dhcp6_client_get_information_request(
 int sd_dhcp6_client_set_request_option(
                 sd_dhcp6_client *client,
                 uint16_t option);
+int sd_dhcp6_client_set_prefix_delegation_hint(
+                sd_dhcp6_client *client,
+                uint8_t prefixlen,
+                const struct in6_addr *pd_address);
 int sd_dhcp6_client_get_prefix_delegation(sd_dhcp6_client *client,
                                           int *delegation);
 int sd_dhcp6_client_set_prefix_delegation(sd_dhcp6_client *client,

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

@@ -99,6 +99,7 @@ UseNTP=
 UseDNS=
 RapidCommit=
 ForceDHCPv6PDOtherInformation=
+PrefixDelegationHint=
 [Route]
 Destination=
 Protocol=