4d739acbdd
The purpose of the changing xid is to prevent misinterpreting delayed messages, and the rare chance where it's randomly the same breaks this sequence-id property.
479 lines
16 KiB
C
479 lines
16 KiB
C
// Copyright 2004-2018 Nicholas J. Kain <njkain at gmail dot com>
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// SPDX-License-Identifier: MIT
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#include <stdlib.h>
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#include <stddef.h>
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#include <stdio.h>
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#include <unistd.h>
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#include <string.h>
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#include <sys/ioctl.h>
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#include <arpa/inet.h>
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#include <sys/types.h>
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#include <netpacket/packet.h>
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#include <net/ethernet.h>
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#include <errno.h>
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#include "nk/log.h"
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#include "nk/io.h"
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#include "nk/random.h"
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#include "nk/net_checksum16.h"
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#include "dhcp.h"
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#include "state.h"
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#include "arp.h"
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#include "ifchange.h"
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#include "sys.h"
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#include "options.h"
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#include "sockd.h"
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static int get_udp_unicast_socket(struct client_state_t *cs)
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{
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char buf[32];
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buf[0] = 'u';
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memcpy(buf + 1, &cs->clientAddr, sizeof cs->clientAddr);
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return request_sockd_fd(buf, 1 + sizeof cs->clientAddr, (char *)0);
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}
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static int get_raw_broadcast_socket(void)
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{
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return request_sockd_fd("s", 1, (char *)0);
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}
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static int get_raw_listen_socket(struct client_state_t *cs)
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{
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char resp;
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int fd = request_sockd_fd("L", 1, &resp);
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switch (resp) {
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case 'L': cs->using_dhcp_bpf = true; break;
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case 'l': cs->using_dhcp_bpf = false; break;
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default: suicide("%s: (%s) expected l or L sockd reply but got %c",
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client_config.interface, __func__, resp);
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}
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return fd;
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}
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// Unicast a DHCP message using a UDP socket.
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static ssize_t send_dhcp_unicast(struct client_state_t *cs,
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struct dhcpmsg *payload)
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{
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ssize_t ret = -1;
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int fd = get_udp_unicast_socket(cs);
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if (fd < 0) {
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log_line("%s: (%s) get_udp_unicast_socket failed",
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client_config.interface, __func__);
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goto out;
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}
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struct sockaddr_in raddr = {
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.sin_family = AF_INET,
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.sin_port = htons(DHCP_SERVER_PORT),
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.sin_addr.s_addr = cs->serverAddr,
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};
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if (connect(fd, (struct sockaddr *)&raddr, sizeof(struct sockaddr)) < 0) {
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log_line("%s: (%s) connect failed: %s", client_config.interface,
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__func__, strerror(errno));
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goto out_fd;
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}
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// Send packets that are as short as possible.
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ssize_t endloc = get_end_option_idx(payload);
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if (endloc < 0) {
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log_line("%s: (%s) No end marker. Not sending.",
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client_config.interface, __func__);
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goto out_fd;
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}
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const size_t el = (size_t)endloc + 1;
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if (el > sizeof payload->options) {
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log_line("%s: (%s) Invalid value of endloc. Not sending.",
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client_config.interface, __func__);
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goto out_fd;
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}
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size_t payload_len =
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sizeof *payload - (sizeof payload->options - el);
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if (!carrier_isup()) {
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log_line("%s: (%s) carrier down; write would fail",
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client_config.interface, __func__);
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ret = -99;
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goto out_fd;
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}
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ret = safe_write(fd, (const char *)payload, payload_len);
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if (ret < 0 || (size_t)ret != payload_len)
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log_line("%s: (%s) write failed: %zd", client_config.interface,
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__func__, ret);
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out_fd:
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close(fd);
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out:
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return ret;
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}
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// Returns 1 if IP checksum is correct, otherwise 0.
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static int ip_checksum(struct ip_udp_dhcp_packet *packet)
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{
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return net_checksum16(&packet->ip, sizeof packet->ip) == 0;
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}
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// Returns 1 if UDP checksum is correct, otherwise 0.
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static int udp_checksum(struct ip_udp_dhcp_packet *packet)
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{
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struct iphdr ph = {
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.saddr = packet->ip.saddr,
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.daddr = packet->ip.daddr,
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.protocol = packet->ip.protocol,
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.tot_len = packet->udp.len,
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};
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uint16_t udpcs =
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net_checksum16(&packet->udp,
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min_size_t(ntohs(packet->udp.len),
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sizeof *packet - sizeof(struct iphdr)));
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uint16_t hdrcs = net_checksum16(&ph, sizeof ph);
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uint16_t cs = net_checksum16_add(udpcs, hdrcs);
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return cs == 0;
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}
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static int get_raw_packet_validate_bpf(struct ip_udp_dhcp_packet *packet)
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{
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if (packet->ip.version != IPVERSION) {
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log_line("%s: IP version is not IPv4.", client_config.interface);
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return 0;
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}
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if (packet->ip.ihl != sizeof packet->ip >> 2) {
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log_line("%s: IP header length incorrect.",
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client_config.interface);
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return 0;
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}
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if (packet->ip.protocol != IPPROTO_UDP) {
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log_line("%s: IP header is not UDP: %d",
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client_config.interface, packet->ip.protocol);
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return 0;
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}
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if (ntohs(packet->udp.dest) != DHCP_CLIENT_PORT) {
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log_line("%s: UDP destination port incorrect: %d",
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client_config.interface, ntohs(packet->udp.dest));
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return 0;
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}
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if (ntohs(packet->udp.len) !=
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ntohs(packet->ip.tot_len) - sizeof packet->ip) {
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log_line("%s: UDP header length incorrect.",
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client_config.interface);
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return 0;
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}
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return 1;
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}
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// Read a packet from a raw socket. Returns -1 on fatal error, -2 on
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// transient error.
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static ssize_t get_raw_packet(struct client_state_t *cs,
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struct dhcpmsg *payload,
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uint32_t *srcaddr)
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{
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struct ip_udp_dhcp_packet packet;
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memset(&packet, 0, sizeof packet);
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ssize_t inc = safe_read(cs->listenFd, (char *)&packet, sizeof packet);
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if (inc < 0) {
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if (errno == EAGAIN || errno == EWOULDBLOCK)
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return -2;
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log_line("%s: (%s) read error %s", client_config.interface,
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__func__, strerror(errno));
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return -1;
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}
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size_t iphdrlen = ntohs(packet.ip.tot_len);
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if ((size_t)inc < iphdrlen)
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return -2;
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if (!cs->using_dhcp_bpf && !get_raw_packet_validate_bpf(&packet))
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return -2;
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if (!ip_checksum(&packet)) {
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log_line("%s: IP header checksum incorrect.",
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client_config.interface);
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return -2;
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}
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if (iphdrlen <= sizeof packet.ip + sizeof packet.udp) {
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log_line("%s: Packet received that is too small (%zu bytes).",
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client_config.interface, iphdrlen);
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return -2;
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}
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size_t l = iphdrlen - sizeof packet.ip - sizeof packet.udp;
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if (l > sizeof *payload) {
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log_line("%s: Packet received that is too long (%zu bytes).",
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client_config.interface, l);
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return -2;
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}
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if (packet.udp.check && !udp_checksum(&packet)) {
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log_line("%s: Packet with bad UDP checksum received. Ignoring.",
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client_config.interface);
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return -2;
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}
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if (srcaddr)
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*srcaddr = packet.ip.saddr;
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memcpy(payload, &packet.data, l);
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return (ssize_t)l;
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}
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// Broadcast a DHCP message using a raw socket.
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static ssize_t send_dhcp_raw(struct dhcpmsg *payload)
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{
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ssize_t ret = -1;
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int fd = get_raw_broadcast_socket();
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if (fd < 0) {
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log_line("%s: (%s) get_raw_broadcast_socket failed",
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client_config.interface, __func__);
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return ret;
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}
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// Send packets that are as short as possible.
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ssize_t endloc = get_end_option_idx(payload);
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if (endloc < 0) {
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log_line("%s: (%s) No end marker. Not sending.",
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client_config.interface, __func__);
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close(fd);
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return ret;
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}
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const size_t el = (size_t)endloc + 1;
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if (el > sizeof payload->options) {
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log_line("%s: (%s) Invalid value of endloc. Not sending.",
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client_config.interface, __func__);
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close(fd);
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return ret;
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}
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size_t padding = sizeof payload->options - el;
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size_t iud_len = sizeof(struct ip_udp_dhcp_packet) - padding;
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size_t ud_len = sizeof(struct udp_dhcp_packet) - padding;
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struct iphdr ph = {
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.saddr = INADDR_ANY,
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.daddr = INADDR_BROADCAST,
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.protocol = IPPROTO_UDP,
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.tot_len = htons(ud_len),
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};
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struct ip_udp_dhcp_packet iudmsg = {
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.ip = {
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.saddr = INADDR_ANY,
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.daddr = INADDR_BROADCAST,
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.protocol = IPPROTO_UDP,
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.tot_len = htons(iud_len),
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.ihl = sizeof iudmsg.ip >> 2,
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.version = IPVERSION,
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.ttl = IPDEFTTL,
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},
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.data = *payload,
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};
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iudmsg.udp.source = htons(DHCP_CLIENT_PORT);
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iudmsg.udp.dest = htons(DHCP_SERVER_PORT);
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iudmsg.udp.len = htons(ud_len);
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iudmsg.udp.check = 0;
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uint16_t udpcs = net_checksum16(&iudmsg.udp, ud_len);
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uint16_t phcs = net_checksum16(&ph, sizeof ph);
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iudmsg.udp.check = net_checksum16_add(udpcs, phcs);
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iudmsg.ip.check = net_checksum16(&iudmsg.ip, sizeof iudmsg.ip);
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struct sockaddr_ll da = {
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.sll_family = AF_PACKET,
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.sll_protocol = htons(ETH_P_IP),
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.sll_pkttype = PACKET_BROADCAST,
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.sll_ifindex = client_config.ifindex,
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.sll_halen = 6,
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};
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memcpy(da.sll_addr, "\xff\xff\xff\xff\xff\xff", 6);
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if (!carrier_isup()) {
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log_line("%s: (%s) carrier down; sendto would fail",
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client_config.interface, __func__);
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ret = -99;
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goto carrier_down;
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}
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ret = safe_sendto(fd, (const char *)&iudmsg, iud_len, 0,
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(struct sockaddr *)&da, sizeof da);
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if (ret < 0 || (size_t)ret != iud_len) {
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if (ret < 0)
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log_line("%s: (%s) sendto failed: %s", client_config.interface,
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__func__, strerror(errno));
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else
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log_line("%s: (%s) sendto short write: %zd < %zu",
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client_config.interface, __func__, ret, iud_len);
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}
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carrier_down:
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close(fd);
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return ret;
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}
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void start_dhcp_listen(struct client_state_t *cs)
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{
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if (cs->listenFd >= 0)
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return;
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cs->listenFd = get_raw_listen_socket(cs);
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if (cs->listenFd < 0)
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suicide("%s: FATAL: Couldn't listen on socket: %s",
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client_config.interface, strerror(errno));
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}
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void stop_dhcp_listen(struct client_state_t *cs)
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{
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if (cs->listenFd < 0)
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return;
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close(cs->listenFd);
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cs->listenFd = -1;
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}
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static int validate_dhcp_packet(struct client_state_t *cs,
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size_t len, struct dhcpmsg *packet,
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uint8_t *msgtype)
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{
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if (len < offsetof(struct dhcpmsg, options)) {
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log_line("%s: Packet is too short to contain magic cookie. Ignoring.",
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client_config.interface);
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return 0;
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}
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if (ntohl(packet->cookie) != DHCP_MAGIC) {
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log_line("%s: Packet with bad magic number. Ignoring.",
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client_config.interface);
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return 0;
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}
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if (packet->xid != cs->xid) {
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log_line("%s: Packet XID %x does not equal our XID %x. Ignoring.",
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client_config.interface, packet->xid, cs->xid);
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return 0;
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}
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if (memcmp(packet->chaddr, client_config.arp, sizeof client_config.arp)) {
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log_line("%s: Packet client MAC %2.2x:%2.2x:%2.2x:%2.2x:%2.2x:%2.2x does not equal our MAC %2.2x:%2.2x:%2.2x:%2.2x:%2.2x:%2.2x. Ignoring it.",
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client_config.interface,
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packet->chaddr[0], packet->chaddr[1], packet->chaddr[2],
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packet->chaddr[3], packet->chaddr[4], packet->chaddr[5],
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client_config.arp[0], client_config.arp[1],
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client_config.arp[2], client_config.arp[3],
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client_config.arp[4], client_config.arp[5]);
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return 0;
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}
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ssize_t endloc = get_end_option_idx(packet);
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if (endloc < 0) {
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log_line("%s: Packet does not have an end option. Ignoring.", client_config.interface);
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return 0;
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}
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*msgtype = get_option_msgtype(packet);
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if (!*msgtype) {
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log_line("%s: Packet does not specify a DHCP message type. Ignoring.",
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client_config.interface);
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return 0;
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}
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char clientid[MAX_DOPT_SIZE];
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size_t cidlen = get_option_clientid(packet, clientid, MAX_DOPT_SIZE);
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if (cidlen == 0)
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return 1;
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if (memcmp(client_config.clientid, clientid,
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min_size_t(cidlen, client_config.clientid_len))) {
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log_line("%s: Packet clientid does not match our clientid. Ignoring.",
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client_config.interface);
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return 0;
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}
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return 1;
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}
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bool dhcp_packet_get(struct client_state_t *cs, struct dhcpmsg *packet,
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uint8_t *msgtype, uint32_t *srcaddr)
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{
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if (cs->listenFd < 0)
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return false;
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ssize_t r = get_raw_packet(cs, packet, srcaddr);
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if (r < 0) {
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// Not a transient issue handled by packet collection functions.
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if (r != -2) {
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log_line("%s: Error reading from listening socket: %s. Reopening.",
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client_config.interface, strerror(errno));
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stop_dhcp_listen(cs);
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start_dhcp_listen(cs);
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}
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return false;
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}
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if (!validate_dhcp_packet(cs, (size_t)r, packet, msgtype))
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return false;
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return true;
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}
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static void add_options_vendor_hostname(struct dhcpmsg *packet)
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{
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size_t vlen = strlen(client_config.vendor);
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size_t hlen = strlen(client_config.hostname);
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if (vlen)
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add_option_vendor(packet, client_config.vendor, vlen);
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else
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add_option_vendor(packet, "ndhc", sizeof "ndhc" - 1);
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add_option_hostname(packet, client_config.hostname, hlen);
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}
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// Initialize a DHCP client packet that will be sent to a server
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static void init_packet(struct dhcpmsg *packet, uint8_t type)
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{
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packet->op = 1; // BOOTREQUEST (client)
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packet->htype = 1; // ETH_10MB
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packet->hlen = 6; // ETH_10MB_LEN
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packet->cookie = htonl(DHCP_MAGIC);
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packet->options[0] = DCODE_END;
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add_option_msgtype(packet, type);
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memcpy(packet->chaddr, client_config.arp, 6);
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add_option_clientid(packet, client_config.clientid,
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client_config.clientid_len);
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}
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ssize_t send_discover(struct client_state_t *cs)
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{
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advance_xid(cs);
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struct dhcpmsg packet = {.xid = cs->xid};
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init_packet(&packet, DHCPDISCOVER);
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if (cs->clientAddr)
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add_option_reqip(&packet, cs->clientAddr);
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add_option_maxsize(&packet);
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add_option_request_list(&packet);
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add_options_vendor_hostname(&packet);
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log_line("%s: Discovering DHCP servers...", client_config.interface);
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return send_dhcp_raw(&packet);
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}
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ssize_t send_selecting(struct client_state_t *cs)
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{
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char clibuf[INET_ADDRSTRLEN];
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struct dhcpmsg packet = {.xid = cs->xid};
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init_packet(&packet, DHCPREQUEST);
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add_option_reqip(&packet, cs->clientAddr);
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add_option_serverid(&packet, cs->serverAddr);
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add_option_maxsize(&packet);
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add_option_request_list(&packet);
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add_options_vendor_hostname(&packet);
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inet_ntop(AF_INET, &(struct in_addr){.s_addr = cs->clientAddr},
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clibuf, sizeof clibuf);
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log_line("%s: Sending a selection request for %s...",
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client_config.interface, clibuf);
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return send_dhcp_raw(&packet);
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}
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ssize_t send_renew_or_rebind(struct client_state_t *cs, bool is_renew)
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{
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struct dhcpmsg packet = {.xid = cs->xid};
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init_packet(&packet, DHCPREQUEST);
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packet.ciaddr = cs->clientAddr;
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add_option_maxsize(&packet);
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add_option_request_list(&packet);
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add_options_vendor_hostname(&packet);
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log_line("%s: Sending a %s request...", client_config.interface,
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is_renew? "renew" : "rebind");
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return is_renew? send_dhcp_unicast(cs, &packet) : send_dhcp_raw(&packet);
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}
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ssize_t send_decline(struct client_state_t *cs, uint32_t server)
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{
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struct dhcpmsg packet = {.xid = cs->xid};
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init_packet(&packet, DHCPDECLINE);
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add_option_reqip(&packet, cs->clientAddr);
|
|
add_option_serverid(&packet, server);
|
|
log_line("%s: Sending a decline message...", client_config.interface);
|
|
return send_dhcp_raw(&packet);
|
|
}
|
|
|
|
ssize_t send_release(struct client_state_t *cs)
|
|
{
|
|
struct dhcpmsg packet = {.xid = nk_random_u32(&cs->rnd_state)};
|
|
init_packet(&packet, DHCPRELEASE);
|
|
packet.ciaddr = cs->clientAddr;
|
|
add_option_reqip(&packet, cs->clientAddr);
|
|
add_option_serverid(&packet, cs->serverAddr);
|
|
log_line("%s: Sending a release message...", client_config.interface);
|
|
return send_dhcp_unicast(cs, &packet);
|
|
}
|
|
|