1c87ae05b3
Per http://tools.ietf.org/html/rfc768: If the computed checksum is zero, it is transmitted as all ones (the equivalent in one's complement arithmetic). An all zero transmitted checksum value means that the transmitter generated no checksum (for debugging or for higher level protocols that don't care). Bug: 10642341 Change-Id: Ib6296dcf3f420f87227047a645c99d9f7ea0d437
241 lines
6.7 KiB
C
241 lines
6.7 KiB
C
/*
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* Copyright 2008, The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include <stdlib.h>
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#include <unistd.h>
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#include <sys/uio.h>
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#include <sys/socket.h>
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#include <netinet/in.h>
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#include <netinet/ip.h>
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#include <netinet/udp.h>
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#include <linux/if_packet.h>
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#include <linux/if_ether.h>
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#include <errno.h>
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#ifdef ANDROID
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#define LOG_TAG "DHCP"
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#include <cutils/log.h>
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#else
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#include <stdio.h>
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#include <string.h>
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#define ALOGD printf
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#define ALOGW printf
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#endif
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#include "dhcpmsg.h"
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int fatal();
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int open_raw_socket(const char *ifname __attribute__((unused)), uint8_t *hwaddr, int if_index)
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{
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int s, flag;
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struct sockaddr_ll bindaddr;
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if((s = socket(PF_PACKET, SOCK_DGRAM, htons(ETH_P_IP))) < 0) {
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return fatal("socket(PF_PACKET)");
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}
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memset(&bindaddr, 0, sizeof(bindaddr));
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bindaddr.sll_family = AF_PACKET;
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bindaddr.sll_protocol = htons(ETH_P_IP);
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bindaddr.sll_halen = ETH_ALEN;
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memcpy(bindaddr.sll_addr, hwaddr, ETH_ALEN);
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bindaddr.sll_ifindex = if_index;
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if (bind(s, (struct sockaddr *)&bindaddr, sizeof(bindaddr)) < 0) {
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return fatal("Cannot bind raw socket to interface");
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}
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return s;
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}
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static uint32_t checksum(void *buffer, unsigned int count, uint32_t startsum)
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{
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uint16_t *up = (uint16_t *)buffer;
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uint32_t sum = startsum;
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uint32_t upper16;
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while (count > 1) {
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sum += *up++;
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count -= 2;
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}
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if (count > 0) {
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sum += (uint16_t) *(uint8_t *)up;
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}
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while ((upper16 = (sum >> 16)) != 0) {
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sum = (sum & 0xffff) + upper16;
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}
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return sum;
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}
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static uint32_t finish_sum(uint32_t sum)
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{
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return ~sum & 0xffff;
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}
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int send_packet(int s, int if_index, struct dhcp_msg *msg, int size,
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uint32_t saddr, uint32_t daddr, uint32_t sport, uint32_t dport)
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{
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struct iphdr ip;
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struct udphdr udp;
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struct iovec iov[3];
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uint32_t udpsum;
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uint16_t temp;
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struct msghdr msghdr;
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struct sockaddr_ll destaddr;
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ip.version = IPVERSION;
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ip.ihl = sizeof(ip) >> 2;
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ip.tos = 0;
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ip.tot_len = htons(sizeof(ip) + sizeof(udp) + size);
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ip.id = 0;
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ip.frag_off = 0;
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ip.ttl = IPDEFTTL;
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ip.protocol = IPPROTO_UDP;
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ip.check = 0;
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ip.saddr = saddr;
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ip.daddr = daddr;
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ip.check = finish_sum(checksum(&ip, sizeof(ip), 0));
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udp.source = htons(sport);
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udp.dest = htons(dport);
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udp.len = htons(sizeof(udp) + size);
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udp.check = 0;
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/* Calculate checksum for pseudo header */
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udpsum = checksum(&ip.saddr, sizeof(ip.saddr), 0);
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udpsum = checksum(&ip.daddr, sizeof(ip.daddr), udpsum);
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temp = htons(IPPROTO_UDP);
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udpsum = checksum(&temp, sizeof(temp), udpsum);
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temp = udp.len;
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udpsum = checksum(&temp, sizeof(temp), udpsum);
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/* Add in the checksum for the udp header */
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udpsum = checksum(&udp, sizeof(udp), udpsum);
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/* Add in the checksum for the data */
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udpsum = checksum(msg, size, udpsum);
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udp.check = finish_sum(udpsum);
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iov[0].iov_base = (char *)&ip;
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iov[0].iov_len = sizeof(ip);
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iov[1].iov_base = (char *)&udp;
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iov[1].iov_len = sizeof(udp);
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iov[2].iov_base = (char *)msg;
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iov[2].iov_len = size;
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memset(&destaddr, 0, sizeof(destaddr));
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destaddr.sll_family = AF_PACKET;
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destaddr.sll_protocol = htons(ETH_P_IP);
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destaddr.sll_ifindex = if_index;
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destaddr.sll_halen = ETH_ALEN;
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memcpy(destaddr.sll_addr, "\xff\xff\xff\xff\xff\xff", ETH_ALEN);
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msghdr.msg_name = &destaddr;
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msghdr.msg_namelen = sizeof(destaddr);
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msghdr.msg_iov = iov;
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msghdr.msg_iovlen = sizeof(iov) / sizeof(struct iovec);
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msghdr.msg_flags = 0;
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msghdr.msg_control = 0;
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msghdr.msg_controllen = 0;
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return sendmsg(s, &msghdr, 0);
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}
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int receive_packet(int s, struct dhcp_msg *msg)
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{
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int nread;
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int is_valid;
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struct dhcp_packet {
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struct iphdr ip;
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struct udphdr udp;
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struct dhcp_msg dhcp;
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} packet;
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int dhcp_size;
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uint32_t sum;
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uint16_t temp;
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uint32_t saddr, daddr;
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nread = read(s, &packet, sizeof(packet));
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if (nread < 0) {
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return -1;
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}
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/*
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* The raw packet interface gives us all packets received by the
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* network interface. We need to filter out all packets that are
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* not meant for us.
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*/
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is_valid = 0;
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if (nread < (int)(sizeof(struct iphdr) + sizeof(struct udphdr))) {
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#if VERBOSE
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ALOGD("Packet is too small (%d) to be a UDP datagram", nread);
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#endif
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} else if (packet.ip.version != IPVERSION || packet.ip.ihl != (sizeof(packet.ip) >> 2)) {
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#if VERBOSE
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ALOGD("Not a valid IP packet");
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#endif
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} else if (nread < ntohs(packet.ip.tot_len)) {
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#if VERBOSE
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ALOGD("Packet was truncated (read %d, needed %d)", nread, ntohs(packet.ip.tot_len));
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#endif
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} else if (packet.ip.protocol != IPPROTO_UDP) {
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#if VERBOSE
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ALOGD("IP protocol (%d) is not UDP", packet.ip.protocol);
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#endif
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} else if (packet.udp.dest != htons(PORT_BOOTP_CLIENT)) {
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#if VERBOSE
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ALOGD("UDP dest port (%d) is not DHCP client", ntohs(packet.udp.dest));
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#endif
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} else {
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is_valid = 1;
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}
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if (!is_valid) {
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return -1;
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}
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/* Seems like it's probably a valid DHCP packet */
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/* validate IP header checksum */
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sum = finish_sum(checksum(&packet.ip, sizeof(packet.ip), 0));
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if (sum != 0) {
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ALOGW("IP header checksum failure (0x%x)", packet.ip.check);
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return -1;
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}
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/*
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* Validate the UDP checksum.
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* Since we don't need the IP header anymore, we "borrow" it
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* to construct the pseudo header used in the checksum calculation.
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*/
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dhcp_size = ntohs(packet.udp.len) - sizeof(packet.udp);
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saddr = packet.ip.saddr;
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daddr = packet.ip.daddr;
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nread = ntohs(packet.ip.tot_len);
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memset(&packet.ip, 0, sizeof(packet.ip));
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packet.ip.saddr = saddr;
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packet.ip.daddr = daddr;
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packet.ip.protocol = IPPROTO_UDP;
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packet.ip.tot_len = packet.udp.len;
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temp = packet.udp.check;
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packet.udp.check = 0;
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sum = finish_sum(checksum(&packet, nread, 0));
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packet.udp.check = temp;
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if (!sum)
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sum = finish_sum(sum);
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if (temp != sum) {
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ALOGW("UDP header checksum failure (0x%x should be 0x%x)", sum, temp);
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return -1;
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}
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memcpy(msg, &packet.dhcp, dhcp_size);
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return dhcp_size;
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}
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