dhcp: Send DHCP Request to acquire an IP address

Create and send a DHCP Request message reusing already existing parts
of the code. This causes factoring out IP and UDP header creation and
moving next timeout calculation to be done every time in the timer
callback function independent of DHCP state. Also add an exponential
part to the timer calculation, bail out if there are errors while
resending the DHCP message for the sixth or more times.

1 files changed, 121 insertions, 39 deletions

diff --git a/src/libsystemd-dhcp/dhcp-client.c b/src/libsystemd-dhcp/dhcp-client.c
index d3ba7ae8ed..4980174e00 100644
--- a/src/libsystemd-dhcp/dhcp-client.c
+++ b/src/libsystemd-dhcp/dhcp-client.c
@@ -56,6 +56,7 @@ struct sd_dhcp_client {
         struct ether_addr mac_addr;
         uint32_t xid;
         usec_t start_time;
+        unsigned int attempt;
         DHCPLease *lease;
 };
 
@@ -151,6 +152,8 @@ static int client_stop(sd_dhcp_client *client, int error)
 
         client->timeout_resend = sd_event_source_unref(client->timeout_resend);
 
+        client->attempt = 1;
+
         switch (client->state) {
 
         case DHCP_STATE_INIT:
@@ -252,6 +255,28 @@ static uint16_t client_checksum(void *buf, int len)
         return ~((sum & 0xffff) + (sum >> 16));
 }
 
+static void client_append_ip_headers(DHCPPacket *packet, uint16_t len)
+{
+        packet->ip.version = IPVERSION;
+        packet->ip.ihl = DHCP_IP_SIZE / 4;
+        packet->ip.tot_len = htobe16(len);
+
+        packet->ip.protocol = IPPROTO_UDP;
+        packet->ip.saddr = INADDR_ANY;
+        packet->ip.daddr = INADDR_BROADCAST;
+
+        packet->udp.source = htobe16(DHCP_PORT_CLIENT);
+        packet->udp.dest = htobe16(DHCP_PORT_SERVER);
+        packet->udp.len = htobe16(len - DHCP_IP_SIZE);
+
+        packet->ip.check = packet->udp.len;
+        packet->udp.check = client_checksum(&packet->ip.ttl, len - 8);
+
+        packet->ip.ttl = IPDEFTTL;
+        packet->ip.check = 0;
+        packet->ip.check = client_checksum(&packet->ip, DHCP_IP_SIZE);
+}
+
 static int client_send_discover(sd_dhcp_client *client, uint16_t secs)
 {
         int err = 0;
@@ -284,29 +309,55 @@ static int client_send_discover(sd_dhcp_client *client, uint16_t secs)
         if (err < 0)
                 return err;
 
-        discover->ip.version = IPVERSION;
-        discover->ip.ihl = sizeof(discover->ip) >> 2;
-        discover->ip.tot_len = htobe16(len);
+        client_append_ip_headers(discover, len);
+
+        err = dhcp_network_send_raw_socket(client->fd, &client->link,
+                                           discover, len);
+
+        return err;
+}
+
+static int client_send_request(sd_dhcp_client *client, uint16_t secs)
+{
+        _cleanup_free_ DHCPPacket *request;
+        size_t optlen, len;
+        int err;
+        uint8_t *opt;
+
+        optlen = DHCP_CLIENT_MIN_OPTIONS_SIZE;
+        len = DHCP_MESSAGE_SIZE + optlen;
+
+        request = malloc0(len);
+        if (!request)
+                return -ENOMEM;
+
+        err = client_packet_init(client, DHCP_REQUEST, &request->dhcp, secs,
+                                 &opt, &optlen);
+        if (err < 0)
+                return err;
 
-        discover->ip.protocol = IPPROTO_UDP;
-        discover->ip.saddr = INADDR_ANY;
-        discover->ip.daddr = INADDR_BROADCAST;
+        if (client->state == DHCP_STATE_REQUESTING) {
+                err = dhcp_option_append(&opt, &optlen,
+                                         DHCP_OPTION_REQUESTED_IP_ADDRESS,
+                                         4, &client->lease->address);
+                if (err < 0)
+                        return err;
 
-        discover->udp.source = htobe16(DHCP_PORT_CLIENT);
-        discover->udp.dest = htobe16(DHCP_PORT_SERVER);
-        discover->udp.len = htobe16(len - sizeof(discover->ip));
+                err = dhcp_option_append(&opt, &optlen,
+                                         DHCP_OPTION_SERVER_IDENTIFIER,
+                                         4, &client->lease->server_address);
+                if (err < 0)
+                        return err;
+        }
 
-        discover->ip.check = discover->udp.len;
-        discover->udp.check = client_checksum(&discover->ip.ttl,
-                                              len - 8);
+        err = dhcp_option_append(&opt, &optlen, DHCP_OPTION_END, 0, NULL);
+        if (err < 0)
+                return err;
 
-        discover->ip.ttl = IPDEFTTL;
-        discover->ip.check = 0;
-        discover->ip.check = client_checksum(&discover->ip,
-                                             sizeof(discover->ip));
+        client_append_ip_headers(request, len);
 
         err = dhcp_network_send_raw_socket(client->fd, &client->link,
-                                           discover, len);
+                                           request, len);
 
         return err;
 }
@@ -319,32 +370,50 @@ static int client_timeout_resend(sd_event_source *s, uint64_t usec,
         uint16_t secs;
         int err = 0;
 
-        switch (client->state) {
-        case DHCP_STATE_INIT:
-        case DHCP_STATE_SELECTING:
+        secs = (usec - client->start_time) / USEC_PER_SEC;
 
-                if (!client->start_time)
-                        client->start_time = usec;
+        if (client->attempt < 64)
+                client->attempt *= 2;
 
-                secs = (usec - client->start_time) / USEC_PER_SEC;
+        next_timeout = usec + (client->attempt - 1) * USEC_PER_SEC +
+                (random_u() & 0x1fffff);
 
-                next_timeout = usec + 2 * USEC_PER_SEC + (random() & 0x1fffff);
+        err = sd_event_add_monotonic(client->event, next_timeout,
+                                     10 * USEC_PER_MSEC,
+                                     client_timeout_resend, client,
+                                     &client->timeout_resend);
+        if (err < 0)
+                goto error;
 
-                err = sd_event_add_monotonic(client->event, next_timeout,
-                                             10 * USEC_PER_MSEC,
-                                             client_timeout_resend, client,
-                                             &client->timeout_resend);
-                if (err < 0)
+        switch (client->state) {
+        case DHCP_STATE_INIT:
+                err = client_send_discover(client, secs);
+                if (err >= 0) {
+                        client->state = DHCP_STATE_SELECTING;
+                        client->attempt = 1;
+                } else {
+                        if (client->attempt >= 64)
+                                goto error;
+                }
+
+                break;
+
+        case DHCP_STATE_SELECTING:
+                err = client_send_discover(client, secs);
+                if (err < 0 && client->attempt >= 64)
                         goto error;
 
-                if (client_send_discover(client, secs) >= 0)
-                        client->state = DHCP_STATE_SELECTING;
+                break;
+
+        case DHCP_STATE_REQUESTING:
+                err = client_send_request(client, secs);
+                if (err < 0 && client->attempt >= 64)
+                         goto error;
 
                 break;
 
         case DHCP_STATE_INIT_REBOOT:
         case DHCP_STATE_REBOOTING:
-        case DHCP_STATE_REQUESTING:
         case DHCP_STATE_BOUND:
         case DHCP_STATE_RENEWING:
         case DHCP_STATE_REBINDING:
@@ -468,11 +537,16 @@ static int client_receive_raw_message(sd_event_source *s, int fd,
         sd_dhcp_client *client = userdata;
         uint8_t buf[sizeof(DHCPPacket) + DHCP_CLIENT_MIN_OPTIONS_SIZE];
         int buflen = sizeof(buf);
-        int len;
+        int len, err = 0;
         DHCPPacket *message;
+        usec_t time_now;
 
         len = read(fd, &buf, buflen);
         if (len < 0)
+                return 0;
+
+        err = sd_event_get_now_monotonic(client->event, &time_now);
+        if (err < 0)
                 goto error;
 
         message = (DHCPPacket *)&buf;
@@ -482,15 +556,18 @@ static int client_receive_raw_message(sd_event_source *s, int fd,
 
                 if (client_receive_offer(client, message, len) >= 0) {
 
-                        client->receive_message =
-                                sd_event_source_unref(client->receive_message);
-                        close(client->fd);
-                        client->fd = -1;
-
                         client->timeout_resend =
                                 sd_event_source_unref(client->timeout_resend);
 
                         client->state = DHCP_STATE_REQUESTING;
+                        client->attempt = 1;
+
+                        err = sd_event_add_monotonic(client->event, time_now, 0,
+                                                     client_timeout_resend,
+                                                     client,
+                                                     &client->timeout_resend);
+                        if (err < 0)
+                                goto error;
                 }
 
                 break;
@@ -507,6 +584,9 @@ static int client_receive_raw_message(sd_event_source *s, int fd,
         }
 
 error:
+        if (err < 0)
+                return client_stop(client, err);
+
         return 0;
 }
 
@@ -535,7 +615,8 @@ int sd_dhcp_client_start(sd_dhcp_client *client)
         if (err < 0)
                 goto error;
 
-        err = sd_event_add_monotonic(client->event, now(CLOCK_MONOTONIC), 0,
+        client->start_time = now(CLOCK_MONOTONIC);
+        err = sd_event_add_monotonic(client->event, client->start_time, 0,
                                      client_timeout_resend, client,
                                      &client->timeout_resend);
         if (err < 0)
@@ -568,6 +649,7 @@ sd_dhcp_client *sd_dhcp_client_new(sd_event *event)
         client->state = DHCP_STATE_INIT;
         client->index = -1;
         client->fd = -1;
+        client->attempt = 1;
 
         client->req_opts_size = ELEMENTSOF(default_req_opts);