sd-dhcp-client: allow getting/setting the client ID

The client identifier can be in many different formats, not just
the one that systemd creates from the Ethernet MAC address.  Non-
ethernet interfaces may have different client IDs formats.  Users
may also have custom client IDs that the wish to use to preserve
lease options delivered by servers configured with the existing
client ID.

2 files changed, 109 insertions, 12 deletions

diff --git a/src/libsystemd-network/sd-dhcp-client.c b/src/libsystemd-network/sd-dhcp-client.c
index 2906f2cb3a..8503f19c27 100644
--- a/src/libsystemd-network/sd-dhcp-client.c
+++ b/src/libsystemd-network/sd-dhcp-client.c
@@ -38,6 +38,7 @@
 #include "dhcp-lease-internal.h"
 #include "sd-dhcp-client.h"
 
+#define MAX_CLIENT_ID_LEN 64  /* Arbitrary limit */
 #define MAX_MAC_ADDR_LEN INFINIBAND_ALEN
 
 struct sd_dhcp_client {
@@ -56,13 +57,33 @@ struct sd_dhcp_client {
         size_t req_opts_allocated;
         size_t req_opts_size;
         be32_t last_addr;
-        struct {
-                uint8_t type;
-                struct ether_addr mac_addr;
-        } _packed_ client_id;
         uint8_t mac_addr[MAX_MAC_ADDR_LEN];
         size_t mac_addr_len;
         uint16_t arp_type;
+        union {
+                struct {
+                        uint8_t type; /* 0: Generic (non-LL) (RFC 2132) */
+                        uint8_t data[MAX_CLIENT_ID_LEN];
+                } _packed_ gen;
+                struct {
+                        uint8_t type; /* 1: Ethernet Link-Layer (RFC 2132) */
+                        uint8_t haddr[ETH_ALEN];
+                } _packed_ eth;
+                struct {
+                        uint8_t type; /* 2 - 254: ARP/Link-Layer (RFC 2132) */
+                        uint8_t haddr[0];
+                } _packed_ ll;
+                struct {
+                        uint8_t type; /* 255: Node-specific (RFC 4361) */
+                        uint8_t iaid[4];
+                        uint8_t duid[MAX_CLIENT_ID_LEN - 4];
+                } _packed_ ns;
+                struct {
+                        uint8_t type;
+                        uint8_t data[MAX_CLIENT_ID_LEN];
+                } _packed_ raw;
+        } client_id;
+        size_t client_id_len;
         char *hostname;
         char *vendor_class_identifier;
         uint32_t mtu;
@@ -200,8 +221,70 @@ int sd_dhcp_client_set_mac(sd_dhcp_client *client, const uint8_t *addr,
         client->mac_addr_len = addr_len;
         client->arp_type = arp_type;
 
-        memcpy(&client->client_id.mac_addr, addr, ETH_ALEN);
-        client->client_id.type = 0x01;
+        if (need_restart && client->state != DHCP_STATE_STOPPED)
+                sd_dhcp_client_start(client);
+
+        return 0;
+}
+
+int sd_dhcp_client_get_client_id(sd_dhcp_client *client, uint8_t *type,
+                                 const uint8_t **data, size_t *data_len) {
+
+        assert_return(client, -EINVAL);
+        assert_return(type, -EINVAL);
+        assert_return(data, -EINVAL);
+        assert_return(data_len, -EINVAL);
+
+        *type = 0;
+        *data = NULL;
+        *data_len = 0;
+        if (client->client_id_len) {
+                *type = client->client_id.raw.type;
+                *data = client->client_id.raw.data;
+                *data_len = client->client_id_len -
+                        sizeof (client->client_id.raw.type);
+        }
+
+        return 0;
+}
+
+int sd_dhcp_client_set_client_id(sd_dhcp_client *client, uint8_t type,
+                                 const uint8_t *data, size_t data_len) {
+        DHCP_CLIENT_DONT_DESTROY(client);
+        bool need_restart = false;
+
+        assert_return(client, -EINVAL);
+        assert_return(data, -EINVAL);
+        assert_return(data_len > 0 && data_len <= MAX_CLIENT_ID_LEN, -EINVAL);
+
+        switch (type) {
+        case ARPHRD_ETHER:
+                if (data_len != ETH_ALEN)
+                        return -EINVAL;
+                break;
+        case ARPHRD_INFINIBAND:
+                if (data_len != INFINIBAND_ALEN)
+                        return -EINVAL;
+                break;
+        default:
+                break;
+        }
+
+        if (client->client_id_len == data_len + sizeof (client->client_id.raw.type) &&
+            client->client_id.raw.type == type &&
+            memcmp(&client->client_id.raw.data, data, data_len) == 0)
+                return 0;
+
+        if (!IN_SET(client->state, DHCP_STATE_INIT, DHCP_STATE_STOPPED)) {
+                log_dhcp_client(client, "Changing client ID on running DHCP "
+                                "client, restarting");
+                need_restart = true;
+                client_stop(client, DHCP_EVENT_STOP);
+        }
+
+        client->client_id.raw.type = type;
+        memcpy(&client->client_id.raw.data, data, data_len);
+        client->client_id_len = data_len + sizeof (client->client_id.raw.type);
 
         if (need_restart && client->state != DHCP_STATE_STOPPED)
                 sd_dhcp_client_start(client);
@@ -378,14 +461,24 @@ static int client_message_init(sd_dhcp_client *client, DHCPPacket **ret,
         if (client->arp_type == ARPHRD_ETHER)
                 memcpy(&packet->dhcp.chaddr, &client->mac_addr, ETH_ALEN);
 
+        /* If no client identifier exists, construct one from an ethernet
+           address if present */
+        if (client->client_id_len == 0 && client->arp_type == ARPHRD_ETHER) {
+                client->client_id.eth.type = ARPHRD_ETHER;
+                memcpy(&client->client_id.eth.haddr, &client->mac_addr, ETH_ALEN);
+                client->client_id_len = sizeof (client->client_id.eth);
+        }
+
         /* Some DHCP servers will refuse to issue an DHCP lease if the Client
            Identifier option is not set */
-        r = dhcp_option_append(&packet->dhcp, optlen, &optoffset, 0,
-                               DHCP_OPTION_CLIENT_IDENTIFIER,
-                               sizeof(client->client_id), &client->client_id);
-        if (r < 0)
-                return r;
-
+        if (client->client_id_len) {
+                r = dhcp_option_append(&packet->dhcp, optlen, &optoffset, 0,
+                                       DHCP_OPTION_CLIENT_IDENTIFIER,
+                                       client->client_id_len,
+                                       &client->client_id.raw);
+                if (r < 0)
+                        return r;
+        }
 
         /* RFC2131 section 3.5:
            in its initial DHCPDISCOVER or DHCPREQUEST message, a
diff --git a/src/systemd/sd-dhcp-client.h b/src/systemd/sd-dhcp-client.h
index 7416f82193..951662e56c 100644
--- a/src/systemd/sd-dhcp-client.h
+++ b/src/systemd/sd-dhcp-client.h
@@ -51,6 +51,10 @@ int sd_dhcp_client_set_request_broadcast(sd_dhcp_client *client, int broadcast);
 int sd_dhcp_client_set_index(sd_dhcp_client *client, int interface_index);
 int sd_dhcp_client_set_mac(sd_dhcp_client *client, const uint8_t *addr,
                            size_t addr_len, uint16_t arp_type);
+int sd_dhcp_client_set_client_id(sd_dhcp_client *client, uint8_t type,
+                                 const uint8_t *data, size_t data_len);
+int sd_dhcp_client_get_client_id(sd_dhcp_client *client, uint8_t *type,
+                                 const uint8_t **data, size_t *data_len);
 int sd_dhcp_client_set_mtu(sd_dhcp_client *client, uint32_t mtu);
 int sd_dhcp_client_set_hostname(sd_dhcp_client *client, const char *hostname);
 int sd_dhcp_client_set_vendor_class_identifier(sd_dhcp_client *client, const char *vci);