sd-dhcp-server: add basic DISCOVER/OFFER support

[thirdparty/systemd.git] / src / libsystemd-network / sd-dhcp-server.c

/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/

/***
  This file is part of systemd.

  Copyright (C) 2013 Intel Corporation. All rights reserved.
  Copyright (C) 2014 Tom Gundersen

  systemd is free software; you can redistribute it and/or modify it
  under the terms of the GNU Lesser General Public License as published by
  the Free Software Foundation; either version 2.1 of the License, or
  (at your option) any later version.

  systemd is distributed in the hope that it will be useful, but
  WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General Public License
  along with systemd; If not, see <http://www.gnu.org/licenses/>.
***/

#include <sys/ioctl.h>
#include <netinet/if_ether.h>

#include "sd-dhcp-server.h"
#include "dhcp-server-internal.h"
#include "dhcp-internal.h"

#define DHCP_DEFAULT_LEASE_TIME         60

int sd_dhcp_server_set_address(sd_dhcp_server *server, struct in_addr *address) {
        assert_return(server, -EINVAL);
        assert_return(address, -EINVAL);
        assert_return(address->s_addr, -EINVAL);
        assert_return(server->address == htobe32(INADDR_ANY), -EBUSY);

        server->address = address->s_addr;

        return 0;
}

sd_dhcp_server *sd_dhcp_server_ref(sd_dhcp_server *server) {
        if (server)
                assert_se(REFCNT_INC(server->n_ref) >= 2);

        return server;
}

sd_dhcp_server *sd_dhcp_server_unref(sd_dhcp_server *server) {
        if (server && REFCNT_DEC(server->n_ref) <= 0) {
                log_dhcp_server(server, "UNREF");

                sd_dhcp_server_stop(server);

                sd_event_unref(server->event);
                free(server);
        }

        return NULL;
}

int sd_dhcp_server_new(sd_dhcp_server **ret, int ifindex) {
        _cleanup_dhcp_server_unref_ sd_dhcp_server *server = NULL;

        assert_return(ret, -EINVAL);
        assert_return(ifindex > 0, -EINVAL);

        server = new0(sd_dhcp_server, 1);
        if (!server)
                return -ENOMEM;

        server->n_ref = REFCNT_INIT;
        server->fd_raw = -1;
        server->fd = -1;
        server->address = htobe32(INADDR_ANY);
        server->index = ifindex;

        *ret = server;
        server = NULL;

        return 0;
}

int sd_dhcp_server_attach_event(sd_dhcp_server *server, sd_event *event, int priority) {
        int r;

        assert_return(server, -EINVAL);
        assert_return(!server->event, -EBUSY);

        if (event)
                server->event = sd_event_ref(event);
        else {
                r = sd_event_default(&server->event);
                if (r < 0)
                        return r;
        }

        server->event_priority = priority;

        return 0;
}

int sd_dhcp_server_detach_event(sd_dhcp_server *server) {
        assert_return(server, -EINVAL);

        server->event = sd_event_unref(server->event);

        return 0;
}

sd_event *sd_dhcp_server_get_event(sd_dhcp_server *server) {
        assert_return(server, NULL);

        return server->event;
}

int sd_dhcp_server_stop(sd_dhcp_server *server) {
        assert_return(server, -EINVAL);

        server->receive_message =
                sd_event_source_unref(server->receive_message);

        server->fd_raw = safe_close(server->fd_raw);
        server->fd = safe_close(server->fd);

        log_dhcp_server(server, "STOPPED");

        return 0;
}

static int dhcp_server_send_unicast_raw(sd_dhcp_server *server, DHCPPacket *packet,
                                        size_t len) {
        union sockaddr_union link = {
                .ll.sll_family = AF_PACKET,
                .ll.sll_protocol = htons(ETH_P_IP),
                .ll.sll_ifindex = server->index,
                .ll.sll_halen = ETH_ALEN,
        };
        int r;

        assert(server);
        assert(server->index > 0);
        assert(server->address);
        assert(packet);
        assert(len > sizeof(DHCPPacket));

        memcpy(&link.ll.sll_addr, &packet->dhcp.chaddr, ETH_ALEN);

        dhcp_packet_append_ip_headers(packet, server->address, DHCP_PORT_SERVER,
                                      packet->dhcp.yiaddr, DHCP_PORT_CLIENT, len);

        r = dhcp_network_send_raw_socket(server->fd_raw, &link, packet, len);
        if (r < 0)
                return r;

        return 0;
}

static int dhcp_server_send_udp(sd_dhcp_server *server, be32_t destination,
                                DHCPMessage *message, size_t len) {
        union sockaddr_union dest = {
                .in.sin_family = AF_INET,
                .in.sin_port = htobe16(DHCP_PORT_CLIENT),
                .in.sin_addr.s_addr = destination,
        };
        struct iovec iov = {
                .iov_base = message,
                .iov_len = len,
        };
        uint8_t cmsgbuf[CMSG_LEN(sizeof(struct in_pktinfo))] = {};
        struct msghdr msg = {
                .msg_name = &dest,
                .msg_namelen = sizeof(dest.in),
                .msg_iov = &iov,
                .msg_iovlen = 1,
                .msg_control = cmsgbuf,
                .msg_controllen = sizeof(cmsgbuf),
        };
        struct cmsghdr *cmsg;
        struct in_pktinfo *pktinfo;
        int r;

        assert(server);
        assert(server->fd > 0);
        assert(message);
        assert(len > sizeof(DHCPMessage));

        cmsg = CMSG_FIRSTHDR(&msg);
        assert(cmsg);

        cmsg->cmsg_level = IPPROTO_IP;
        cmsg->cmsg_type = IP_PKTINFO;
        cmsg->cmsg_len = CMSG_LEN(sizeof(struct in_pktinfo));

        /* we attach source interface and address info to the message
           rather than binding the socket. This will be mostly useful
           when we gain support for arbitrary number of server addresses
         */
        pktinfo = (struct in_pktinfo*) CMSG_DATA(cmsg);
        assert(pktinfo);

        pktinfo->ipi_ifindex = server->index;
        pktinfo->ipi_spec_dst.s_addr = server->address;

        r = sendmsg(server->fd, &msg, 0);
        if (r < 0)
                return -errno;

        return 0;
}

static bool requested_broadcast(DHCPRequest *req) {
        assert(req);

        return req->message->flags & htobe16(0x8000);
}

int dhcp_server_send_packet(sd_dhcp_server *server,
                            DHCPRequest *req, DHCPPacket *packet,
                            int type, size_t optoffset) {
        be32_t destination = INADDR_ANY;
        int r;

        assert(server);
        assert(req);
        assert(req->max_optlen);
        assert(optoffset <= req->max_optlen);
        assert(packet);

        r = dhcp_option_append(&packet->dhcp, req->max_optlen, &optoffset, 0,
                               DHCP_OPTION_SERVER_IDENTIFIER,
                               4, &server->address);
        if (r < 0)
                return r;

        r = dhcp_option_append(&packet->dhcp, req->max_optlen, &optoffset, 0,
                               DHCP_OPTION_END, 0, NULL);
        if (r < 0)
                return r;

        /* RFC 2131 Section 4.1

           If the ’giaddr’ field in a DHCP message from a client is non-zero,
           the server sends any return messages to the ’DHCP server’ port on the
           BOOTP relay agent whose address appears in ’giaddr’. If the ’giaddr’
           field is zero and the ’ciaddr’ field is nonzero, then the server
           unicasts DHCPOFFER and DHCPACK messages to the address in ’ciaddr’.
           If ’giaddr’ is zero and ’ciaddr’ is zero, and the broadcast bit is
           set, then the server broadcasts DHCPOFFER and DHCPACK messages to
           0xffffffff. If the broadcast bit is not set and ’giaddr’ is zero and
           ’ciaddr’ is zero, then the server unicasts DHCPOFFER and DHCPACK
           messages to the client’s hardware address and ’yiaddr’ address. In
           all cases, when ’giaddr’ is zero, the server broadcasts any DHCPNAK
           messages to 0xffffffff.

           Section 4.3.2

           If ’giaddr’ is set in the DHCPREQUEST message, the client is on a
           different subnet. The server MUST set the broadcast bit in the
           DHCPNAK, so that the relay agent will broadcast the DHCPNAK to the
           client, because the client may not have a correct network address
           or subnet mask, and the client may not be answering ARP requests.
         */
        if (req->message->giaddr) {
                destination = req->message->giaddr;
                if (type == DHCP_NAK)
                        packet->dhcp.flags = htobe16(0x8000);
        } else if (req->message->ciaddr && type != DHCP_NAK)
                destination = req->message->ciaddr;

        if (destination || requested_broadcast(req) || type == DHCP_NAK)
                return dhcp_server_send_udp(server, destination, &packet->dhcp,
                                            sizeof(DHCPMessage) + optoffset);
        else
                /* we cannot send UDP packet to specific MAC address when the address is
                   not yet configured, so must fall back to raw packets */
                return dhcp_server_send_unicast_raw(server, packet,
                                                    sizeof(DHCPPacket) + optoffset);
}

static int server_message_init(sd_dhcp_server *server, DHCPPacket **ret,
                               uint8_t type, size_t *_optoffset, DHCPRequest *req) {
        _cleanup_free_ DHCPPacket *packet = NULL;
        size_t optoffset;
        int r;

        assert(server);
        assert(ret);
        assert(_optoffset);
        assert(type == DHCP_OFFER);

        packet = malloc0(sizeof(DHCPPacket) + req->max_optlen);
        if (!packet)
                return -ENOMEM;

        r = dhcp_message_init(&packet->dhcp, BOOTREPLY, be32toh(req->message->xid),
                              type, req->max_optlen, &optoffset);
        if (r < 0)
                return r;

        packet->dhcp.flags = req->message->flags;
        packet->dhcp.giaddr = req->message->giaddr;
        memcpy(&packet->dhcp.chaddr, &req->message->chaddr, ETH_ALEN);

        *_optoffset = optoffset;
        *ret = packet;
        packet = NULL;

        return 0;
}

static int server_send_offer(sd_dhcp_server *server, DHCPRequest *req) {
        _cleanup_free_ DHCPPacket *packet = NULL;
        size_t offset;
        be32_t lease_time;
        int r;

        r = server_message_init(server, &packet, DHCP_OFFER, &offset, req);
        if (r < 0)
                return r;

        /* for now offer a random IP */
        packet->dhcp.yiaddr = random_u32();

        /* for one minute */
        lease_time = htobe32(DHCP_DEFAULT_LEASE_TIME);
        r = dhcp_option_append(&packet->dhcp, req->max_optlen, &offset, 0,
                               DHCP_OPTION_IP_ADDRESS_LEASE_TIME, 4, &lease_time);
        if (r < 0)
                return r;

        r = dhcp_server_send_packet(server, req, packet, DHCP_OFFER, offset);
        if (r < 0)
                return r;

        return 0;
}

static int parse_request(uint8_t code, uint8_t len, const uint8_t *option,
                         void *user_data) {
        DHCPRequest *req = user_data;

        assert(req);

        switch(code) {
        case DHCP_OPTION_SERVER_IDENTIFIER:
                if (len == 4)
                        req->server_id = *(be32_t*)option;

                break;
        case DHCP_OPTION_CLIENT_IDENTIFIER:
                if (len >= 2) {
                        uint8_t *data;

                        data = memdup(option, len);
                        if (!data)
                                return -ENOMEM;

                        free(req->client_id.data);
                        req->client_id.data = data;
                        req->client_id.length = len;
                }

                break;
        case DHCP_OPTION_MAXIMUM_MESSAGE_SIZE:
                if (len == 2)
                        req->max_optlen = be16toh(*(be16_t*)option) -
                                          - sizeof(DHCPPacket);

                break;
        }

        return 0;
}

static void dhcp_request_free(DHCPRequest *req) {
        if (!req)
                return;

        free(req->client_id.data);
        free(req);
}

DEFINE_TRIVIAL_CLEANUP_FUNC(DHCPRequest*, dhcp_request_free);
#define _cleanup_dhcp_request_free_ _cleanup_(dhcp_request_freep)

static int ensure_sane_request(DHCPRequest *req, DHCPMessage *message) {
        assert(req);
        assert(message);

        req->message = message;

        /* set client id based on mac address if client did not send an explicit one */
        if (!req->client_id.data) {
                uint8_t *data;

                data = new0(uint8_t, ETH_ALEN + 1);
                if (!data)
                        return -ENOMEM;

                req->client_id.length = ETH_ALEN + 1;
                req->client_id.data = data;
                req->client_id.data[0] = 0x01;
                memcpy(&req->client_id.data[1], &message->chaddr, ETH_ALEN);
        }

        if (req->max_optlen < DHCP_MIN_OPTIONS_SIZE)
                req->max_optlen = DHCP_MIN_OPTIONS_SIZE;

        return 0;
}

int dhcp_server_handle_message(sd_dhcp_server *server, DHCPMessage *message,
                               size_t length) {
        _cleanup_dhcp_request_free_ DHCPRequest *req = NULL;
        int type, r;

        assert(server);
        assert(message);

        if (message->op != BOOTREQUEST ||
            message->htype != ARPHRD_ETHER ||
            message->hlen != ETHER_ADDR_LEN)
                return 0;

        req = new0(DHCPRequest, 1);
        if (!req)
                return -ENOMEM;

        type = dhcp_option_parse(message, length, parse_request, req);
        if (type < 0)
                return 0;

        r = ensure_sane_request(req, message);
        if (r < 0)
                /* this only fails on critical errors */
                return r;

        switch(type) {
        case DHCP_DISCOVER:
                log_dhcp_server(server, "DISCOVER (0x%x)",
                                be32toh(req->message->xid));

                r = server_send_offer(server, req);
                if (r < 0) {
                        /* this only fails on critical errors */
                        log_dhcp_server(server, "could not send offer: %s",
                                        strerror(-r));
                        return r;
                } else {
                        log_dhcp_server(server, "OFFER (0x%x)",
                                        be32toh(req->message->xid));
                        return DHCP_OFFER;
                }

                break;
        }

        return 0;
}

static int server_receive_message(sd_event_source *s, int fd,
                                  uint32_t revents, void *userdata) {
        _cleanup_free_ DHCPMessage *message = NULL;
        uint8_t cmsgbuf[CMSG_LEN(sizeof(struct in_pktinfo))];
        sd_dhcp_server *server = userdata;
        struct iovec iov = {};
        struct msghdr msg = {
                .msg_iov = &iov,
                .msg_iovlen = 1,
                .msg_control = cmsgbuf,
                .msg_controllen = sizeof(cmsgbuf),
        };
        struct cmsghdr *cmsg;
        int buflen = 0, len, r;

        assert(server);

        r = ioctl(fd, FIONREAD, &buflen);
        if (r < 0)
                return r;
        if (buflen < 0)
                return -EIO;

        message = malloc0(buflen);
        if (!message)
                return -ENOMEM;

        iov.iov_base = message;
        iov.iov_len = buflen;

        len = recvmsg(fd, &msg, 0);
        if (len < buflen)
                return 0;
        else if ((size_t)len < sizeof(DHCPMessage))
                return 0;

        for (cmsg = CMSG_FIRSTHDR(&msg); cmsg; cmsg = CMSG_NXTHDR(&msg, cmsg)) {
                if (cmsg->cmsg_level == IPPROTO_IP &&
                    cmsg->cmsg_type == IP_PKTINFO &&
                    cmsg->cmsg_len == CMSG_LEN(sizeof(struct in_pktinfo))) {
                        struct in_pktinfo *info = (struct in_pktinfo*)CMSG_DATA(cmsg);

                        /* TODO figure out if this can be done as a filter on the socket, like for IPv6 */
                        if (server->index != info->ipi_ifindex)
                                return 0;

                        break;
                }
        }

        return dhcp_server_handle_message(server, message, (size_t)len);
}

int sd_dhcp_server_start(sd_dhcp_server *server) {
        int r;

        assert_return(server, -EINVAL);
        assert_return(server->event, -EINVAL);
        assert_return(!server->receive_message, -EBUSY);
        assert_return(server->fd_raw == -1, -EBUSY);
        assert_return(server->fd == -1, -EBUSY);
        assert_return(server->address != htobe32(INADDR_ANY), -EUNATCH);

        r = socket(AF_PACKET, SOCK_DGRAM | SOCK_NONBLOCK, 0);
        if (r < 0) {
                r = -errno;
                sd_dhcp_server_stop(server);
                return r;
        }
        server->fd_raw = r;

        r = dhcp_network_bind_udp_socket(INADDR_ANY, DHCP_PORT_SERVER);
        if (r < 0) {
                sd_dhcp_server_stop(server);
                return r;
        }
        server->fd = r;

        r = sd_event_add_io(server->event, &server->receive_message,
                            server->fd, EPOLLIN,
                            server_receive_message, server);
        if (r < 0) {
                sd_dhcp_server_stop(server);
                return r;
        }

        r = sd_event_source_set_priority(server->receive_message,
                                         server->event_priority);
        if (r < 0) {
                sd_dhcp_server_stop(server);
                return r;
        }

        log_dhcp_server(server, "STARTED");

        return 0;
}