sd-dhcp: split out packet handling from client

1 files changed, 171 insertions, 0 deletions

diff --git a/src/libsystemd-dhcp/dhcp-packet.c b/src/libsystemd-dhcp/dhcp-packet.c
new file mode 100644
index 0000000000..d606d55a05
--- /dev/null
+++ b/src/libsystemd-dhcp/dhcp-packet.c
@@ -0,0 +1,171 @@
+/***
+  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 <stdlib.h>
+#include <errno.h>
+#include <string.h>
+#include <stdio.h>
+#include <net/ethernet.h>
+#include <net/if_arp.h>
+#include <sys/param.h>
+
+#include "util.h"
+#include "list.h"
+
+#include "dhcp-protocol.h"
+#include "dhcp-lease.h"
+#include "dhcp-internal.h"
+#include "sd-dhcp-client.h"
+
+#define DHCP_CLIENT_MIN_OPTIONS_SIZE            312
+
+int dhcp_message_init(DHCPMessage *message, uint8_t op, uint32_t xid,
+                      uint8_t type, uint16_t secs, uint8_t **opt,
+                      size_t *optlen) {
+        int err;
+
+        *opt = (uint8_t *)(message + 1);
+
+        if (*optlen < 4)
+                return -ENOBUFS;
+        *optlen -= 4;
+
+        message->op = op;
+        message->htype = ARPHRD_ETHER;
+        message->hlen = ETHER_ADDR_LEN;
+        message->xid = htobe32(xid);
+
+        /* Although 'secs' field is a SHOULD in RFC 2131, certain DHCP servers
+           refuse to issue an DHCP lease if 'secs' is set to zero */
+        message->secs = htobe16(secs);
+
+        (*opt)[0] = 0x63;
+        (*opt)[1] = 0x82;
+        (*opt)[2] = 0x53;
+        (*opt)[3] = 0x63;
+
+        *opt += 4;
+
+        err = dhcp_option_append(opt, optlen, DHCP_OPTION_MESSAGE_TYPE, 1,
+                                 &type);
+        if (err < 0)
+                return err;
+
+        return 0;
+}
+
+static uint16_t dhcp_checksum(void *buf, int len) {
+        uint32_t sum;
+        uint16_t *check;
+        int i;
+        uint8_t *odd;
+
+        sum = 0;
+        check = buf;
+
+        for (i = 0; i < len / 2 ; i++)
+                sum += check[i];
+
+        if (len & 0x01) {
+                odd = buf;
+                sum += odd[len - 1];
+        }
+
+        while (sum >> 16)
+                sum = (sum & 0xffff) + (sum >> 16);
+
+        return ~sum;
+}
+
+void dhcp_packet_append_ip_headers(DHCPPacket *packet, uint8_t op,
+                                   uint16_t len) {
+        assert(op == BOOTREQUEST || op == BOOTREPLY);
+
+        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;
+
+        switch (op) {
+                case BOOTREQUEST:
+                        packet->udp.source = htobe16(DHCP_PORT_CLIENT);
+                        packet->udp.dest = htobe16(DHCP_PORT_SERVER);
+                        break;
+                case BOOTREPLY:
+                        packet->udp.source = htobe16(DHCP_PORT_SERVER);
+                        packet->udp.dest = htobe16(DHCP_PORT_CLIENT);
+                        break;
+        }
+
+        packet->udp.len = htobe16(len - DHCP_IP_SIZE);
+
+        packet->ip.check = packet->udp.len;
+        packet->udp.check = dhcp_checksum(&packet->ip.ttl, len - 8);
+
+        packet->ip.ttl = IPDEFTTL;
+        packet->ip.check = 0;
+        packet->ip.check = dhcp_checksum(&packet->ip, DHCP_IP_SIZE);
+}
+
+int dhcp_packet_verify_headers(DHCPPacket *packet, uint8_t op, size_t len) {
+        size_t hdrlen;
+
+        assert(op == BOOTREQUEST || op == BOOTREPLY);
+
+        if (len < (DHCP_IP_UDP_SIZE + DHCP_MESSAGE_SIZE))
+                return -EINVAL;
+
+        hdrlen = packet->ip.ihl * 4;
+        if (hdrlen < 20 || hdrlen > len || dhcp_checksum(&packet->ip, hdrlen))
+                return -EINVAL;
+
+        if (hdrlen + be16toh(packet->udp.len) > len)
+                return -EINVAL;
+
+        if (packet->udp.check) {
+                packet->ip.check = packet->udp.len;
+                packet->ip.ttl = 0;
+
+                if (dhcp_checksum(&packet->ip.ttl,
+                                  be16toh(packet->udp.len) + 12))
+                        return -EINVAL;
+        }
+
+        if (packet->dhcp.op != op)
+                return -EINVAL;
+
+        switch (op) {
+                case BOOTREQUEST:
+                        if (be16toh(packet->udp.source) != DHCP_PORT_CLIENT ||
+                            be16toh(packet->udp.dest) != DHCP_PORT_SERVER)
+                                return -EINVAL;
+                        break;
+                case BOOTREPLY:
+                        if (be16toh(packet->udp.source) != DHCP_PORT_SERVER ||
+                            be16toh(packet->udp.dest) != DHCP_PORT_CLIENT)
+                                return -EINVAL;
+                        break;
+        }
+
+        return 0;
+}