1/*
2 * Copyright 2008, The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *     http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17#include <stdlib.h>
18#include <unistd.h>
19#include <sys/uio.h>
20#include <sys/socket.h>
21#include <netinet/in.h>
22#include <netinet/ip.h>
23#include <netinet/udp.h>
24#include <linux/if_packet.h>
25#include <linux/if_ether.h>
26#include <errno.h>
27
28#ifdef ANDROID
29#define LOG_TAG "DHCP"
30#include <cutils/log.h>
31#else
32#include <stdio.h>
33#include <string.h>
34#define ALOGD printf
35#define ALOGW printf
36#endif
37
38#include "dhcpmsg.h"
39
40int fatal();
41
42int open_raw_socket(const char *ifname __attribute__((unused)), uint8_t *hwaddr, int if_index)
43{
44    int s, flag;
45    struct sockaddr_ll bindaddr;
46
47    if((s = socket(PF_PACKET, SOCK_DGRAM, htons(ETH_P_IP))) < 0) {
48        return fatal("socket(PF_PACKET)");
49    }
50
51    memset(&bindaddr, 0, sizeof(bindaddr));
52    bindaddr.sll_family = AF_PACKET;
53    bindaddr.sll_protocol = htons(ETH_P_IP);
54    bindaddr.sll_halen = ETH_ALEN;
55    memcpy(bindaddr.sll_addr, hwaddr, ETH_ALEN);
56    bindaddr.sll_ifindex = if_index;
57
58    if (bind(s, (struct sockaddr *)&bindaddr, sizeof(bindaddr)) < 0) {
59        return fatal("Cannot bind raw socket to interface");
60    }
61
62    return s;
63}
64
65static uint32_t checksum(void *buffer, unsigned int count, uint32_t startsum)
66{
67    uint16_t *up = (uint16_t *)buffer;
68    uint32_t sum = startsum;
69    uint32_t upper16;
70
71    while (count > 1) {
72        sum += *up++;
73        count -= 2;
74    }
75    if (count > 0) {
76        sum += (uint16_t) *(uint8_t *)up;
77    }
78    while ((upper16 = (sum >> 16)) != 0) {
79        sum = (sum & 0xffff) + upper16;
80    }
81    return sum;
82}
83
84static uint32_t finish_sum(uint32_t sum)
85{
86    return ~sum & 0xffff;
87}
88
89int send_packet(int s, int if_index, struct dhcp_msg *msg, int size,
90                uint32_t saddr, uint32_t daddr, uint32_t sport, uint32_t dport)
91{
92    struct iphdr ip;
93    struct udphdr udp;
94    struct iovec iov[3];
95    uint32_t udpsum;
96    uint16_t temp;
97    struct msghdr msghdr;
98    struct sockaddr_ll destaddr;
99
100    ip.version = IPVERSION;
101    ip.ihl = sizeof(ip) >> 2;
102    ip.tos = 0;
103    ip.tot_len = htons(sizeof(ip) + sizeof(udp) + size);
104    ip.id = 0;
105    ip.frag_off = 0;
106    ip.ttl = IPDEFTTL;
107    ip.protocol = IPPROTO_UDP;
108    ip.check = 0;
109    ip.saddr = saddr;
110    ip.daddr = daddr;
111    ip.check = finish_sum(checksum(&ip, sizeof(ip), 0));
112
113    udp.source = htons(sport);
114    udp.dest = htons(dport);
115    udp.len = htons(sizeof(udp) + size);
116    udp.check = 0;
117
118    /* Calculate checksum for pseudo header */
119    udpsum = checksum(&ip.saddr, sizeof(ip.saddr), 0);
120    udpsum = checksum(&ip.daddr, sizeof(ip.daddr), udpsum);
121    temp = htons(IPPROTO_UDP);
122    udpsum = checksum(&temp, sizeof(temp), udpsum);
123    temp = udp.len;
124    udpsum = checksum(&temp, sizeof(temp), udpsum);
125
126    /* Add in the checksum for the udp header */
127    udpsum = checksum(&udp, sizeof(udp), udpsum);
128
129    /* Add in the checksum for the data */
130    udpsum = checksum(msg, size, udpsum);
131    udp.check = finish_sum(udpsum);
132
133    iov[0].iov_base = (char *)&ip;
134    iov[0].iov_len = sizeof(ip);
135    iov[1].iov_base = (char *)&udp;
136    iov[1].iov_len = sizeof(udp);
137    iov[2].iov_base = (char *)msg;
138    iov[2].iov_len = size;
139    memset(&destaddr, 0, sizeof(destaddr));
140    destaddr.sll_family = AF_PACKET;
141    destaddr.sll_protocol = htons(ETH_P_IP);
142    destaddr.sll_ifindex = if_index;
143    destaddr.sll_halen = ETH_ALEN;
144    memcpy(destaddr.sll_addr, "\xff\xff\xff\xff\xff\xff", ETH_ALEN);
145
146    msghdr.msg_name = &destaddr;
147    msghdr.msg_namelen = sizeof(destaddr);
148    msghdr.msg_iov = iov;
149    msghdr.msg_iovlen = sizeof(iov) / sizeof(struct iovec);
150    msghdr.msg_flags = 0;
151    msghdr.msg_control = 0;
152    msghdr.msg_controllen = 0;
153    return sendmsg(s, &msghdr, 0);
154}
155
156int receive_packet(int s, struct dhcp_msg *msg)
157{
158    int nread;
159    int is_valid;
160    struct dhcp_packet {
161        struct iphdr ip;
162        struct udphdr udp;
163        struct dhcp_msg dhcp;
164    } packet;
165    int dhcp_size;
166    uint32_t sum;
167    uint16_t temp;
168    uint32_t saddr, daddr;
169
170    nread = read(s, &packet, sizeof(packet));
171    if (nread < 0) {
172        return -1;
173    }
174    /*
175     * The raw packet interface gives us all packets received by the
176     * network interface. We need to filter out all packets that are
177     * not meant for us.
178     */
179    is_valid = 0;
180    if (nread < (int)(sizeof(struct iphdr) + sizeof(struct udphdr))) {
181#if VERBOSE
182        ALOGD("Packet is too small (%d) to be a UDP datagram", nread);
183#endif
184    } else if (packet.ip.version != IPVERSION || packet.ip.ihl != (sizeof(packet.ip) >> 2)) {
185#if VERBOSE
186        ALOGD("Not a valid IP packet");
187#endif
188    } else if (nread < ntohs(packet.ip.tot_len)) {
189#if VERBOSE
190        ALOGD("Packet was truncated (read %d, needed %d)", nread, ntohs(packet.ip.tot_len));
191#endif
192    } else if (packet.ip.protocol != IPPROTO_UDP) {
193#if VERBOSE
194        ALOGD("IP protocol (%d) is not UDP", packet.ip.protocol);
195#endif
196    } else if (packet.udp.dest != htons(PORT_BOOTP_CLIENT)) {
197#if VERBOSE
198        ALOGD("UDP dest port (%d) is not DHCP client", ntohs(packet.udp.dest));
199#endif
200    } else {
201        is_valid = 1;
202    }
203
204    if (!is_valid) {
205        return -1;
206    }
207
208    /* Seems like it's probably a valid DHCP packet */
209    /* validate IP header checksum */
210    sum = finish_sum(checksum(&packet.ip, sizeof(packet.ip), 0));
211    if (sum != 0) {
212        ALOGW("IP header checksum failure (0x%x)", packet.ip.check);
213        return -1;
214    }
215    /*
216     * Validate the UDP checksum.
217     * Since we don't need the IP header anymore, we "borrow" it
218     * to construct the pseudo header used in the checksum calculation.
219     */
220    dhcp_size = ntohs(packet.udp.len) - sizeof(packet.udp);
221    saddr = packet.ip.saddr;
222    daddr = packet.ip.daddr;
223    nread = ntohs(packet.ip.tot_len);
224    memset(&packet.ip, 0, sizeof(packet.ip));
225    packet.ip.saddr = saddr;
226    packet.ip.daddr = daddr;
227    packet.ip.protocol = IPPROTO_UDP;
228    packet.ip.tot_len = packet.udp.len;
229    temp = packet.udp.check;
230    packet.udp.check = 0;
231    sum = finish_sum(checksum(&packet, nread, 0));
232    packet.udp.check = temp;
233    if (!sum)
234        sum = finish_sum(sum);
235    if (temp != sum) {
236        ALOGW("UDP header checksum failure (0x%x should be 0x%x)", sum, temp);
237        return -1;
238    }
239    memcpy(msg, &packet.dhcp, dhcp_size);
240    return dhcp_size;
241}
242