我遇到一个问题，示例程序（复制如下）生成的 tcp 校验和与wireshark 计算的校验和不匹配。有人可以指出我哪里出错了吗？
这里我尝试了两种方法
- tcp_校验和
- get_ipv6_udptcp_checksum。
有了这两个值，就会得到两个不同的值，并且都与wireshark值不匹配。
我在此处复制 IP 和 TCP 标头详细信息。
IP 标头：
0000 60 00 00 00 00 2a 06 80 10 80 a2 b1 00 00 00 00
0010 00 00 00 00 00 1e 00 00 00 00 00 00 00 00 00
0020 00 00 00 00 00 00 00 24
TCP 标头：
0000 04 22 00 50 00 01 e0 日 00 01 42 74 50 14 2238
0010 eb10 00 00
我的理解是，添加伪标头和 TCP 标头值将给出校验和。手动添加值会给出完全不同的值。当我尝试以编程方式时，它是（38 eb）。 wireshark显示正确的值应该是0xb348
我哪里做错了？有人可以建议我如何手动完成吗？
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h> // close()
#include <string.h> // strcpy, memset(), and memcpy()
#include <netdb.h> // struct addrinfo
#include <sys/types.h> // needed for socket(), uint8_t, uint16_t
#include <sys/socket.h> // needed for socket()
#include <netinet/in.h> // IPPROTO_TCP, INET6_ADDRSTRLEN
#include <netinet/ip.h> // IP_MAXPACKET (which is 65535)
#include <netinet/ip6.h> // struct ip6_hdr
#define __FAVOR_BSD // Use BSD format of tcp header
#include <netinet/tcp.h> // struct tcphdr
#include <arpa/inet.h> // inet_pton() and inet_ntop()
#include <sys/ioctl.h> // macro ioctl is defined
#include <bits/ioctls.h> // defines values for argument "request" of ioctl.
#include <net/if.h> // struct ifreq
#include <linux/if_ether.h> // ETH_P_IP = 0x0800, ETH_P_IPV6 = 0x86DD
#include <linux/if_packet.h> // struct sockaddr_ll (see man 7 packet)
#include <net/ethernet.h>
#include <errno.h> // errno, perror()
void ipv6_to_str_unexpanded(char *str, const struct in6_addr * addr) {
sprintf(str, "%02x%02x:%02x%02x:%02x%02x:%02x%02x:%02x%02x:%02x%02x:%02x%02x:%02x%02x",
(int)addr->s6_addr[0], (int)addr->s6_addr[1],
(int)addr->s6_addr[2], (int)addr->s6_addr[3],
(int)addr->s6_addr[4], (int)addr->s6_addr[5],
(int)addr->s6_addr[6], (int)addr->s6_addr[7],
(int)addr->s6_addr[8], (int)addr->s6_addr[9],
(int)addr->s6_addr[10], (int)addr->s6_addr[11],
(int)addr->s6_addr[12], (int)addr->s6_addr[13],
(int)addr->s6_addr[14], (int)addr->s6_addr[15]);
printf("addr:[%s]\n",str);
}
static inline uint16_t
get_16b_sum(uint16_t *ptr16, uint32_t nr)
{
uint32_t sum = 0;
while (nr > 1)
{
sum +=*ptr16;
nr -= sizeof(uint16_t);
ptr16++;
if (sum > UINT16_MAX)
sum -= UINT16_MAX;
}
/* If length is in odd bytes */
if (nr)
sum += *((uint8_t*)ptr16);
sum = ((sum & 0xffff0000) >> 16) + (sum & 0xffff);
sum &= 0x0ffff;
return (uint16_t)sum;
}
static inline uint16_t
get_ipv6_psd_sum (struct ip6_hdr * ip_hdr)
{
/* Pseudo Header for IPv6/UDP/TCP checksum */
union ipv6_psd_header {
struct {
uint8_t src_addr[16]; /* IP address of source host. */
uint8_t dst_addr[16]; /* IP address of destination host(s). */
uint32_t len; /* L4 length. */
uint32_t proto; /* L4 protocol - top 3 bytes must be zero */
} __attribute__((__packed__));
uint16_t u16_arr[0]; /* allow use as 16-bit values with safe aliasing */
} psd_hdr;
memcpy(&psd_hdr.src_addr, &ip_hdr->ip6_src,
(sizeof(ip_hdr->ip6_src) + sizeof(ip_hdr->ip6_dst)));
//psd_hdr.len = ip_hdr->payload_len;
psd_hdr.len = ip_hdr->ip6_plen;
psd_hdr.proto = IPPROTO_TCP;//(ip_hdr->proto << 24);
return get_16b_sum(psd_hdr.u16_arr, sizeof(psd_hdr));
}
static inline uint16_t
get_ipv6_udptcp_checksum(struct ip6_hdr *ipv6_hdr, uint16_t *l4_hdr)
{
uint32_t cksum;
uint32_t l4_len;
l4_len = (ipv6_hdr->ip6_plen);
cksum = get_16b_sum(l4_hdr, l4_len);
cksum += get_ipv6_psd_sum(ipv6_hdr);
cksum = ((cksum & 0xffff0000) >> 16) + (cksum & 0xffff);
cksum = (~cksum) & 0xffff;
if (cksum == 0)
cksum = 0xffff;
return (uint16_t)cksum;
}
//! \brief Calculate the TCP checksum.
//! \param buff The TCP packet.
//! \param len The size of the TCP packet.
//! \param src_addr The IP source address (in network format).
//! \param dest_addr The IP destination address (in network format).
//! \return The result of the checksum.
uint16_t tcp_checksum(const void *buff, size_t len, struct in6_addr src_addr, struct in6_addr dest_addr)
{
const uint16_t *buf=buff;
uint16_t *ip_src=(void *)&src_addr, *ip_dst=(void *)&dest_addr;
uint32_t sum;
size_t length=len;
// Calculate the sum //
sum = 0;
while (len > 1)
{
sum += *buf++;
if (sum & 0x80000000)
sum = (sum & 0xFFFF) + (sum >> 16);
len -= 2;
}
if ( len & 1 )
// Add the padding if the packet lenght is odd //
sum += *((uint8_t *)buf);
// Add the pseudo-header //
sum += *(ip_src++);
sum += *ip_src;
sum += *(ip_dst++);
sum += *ip_dst;
sum += htons(IPPROTO_TCP);
sum += htons(length);
// Add the carries //
while (sum >> 16)
sum = (sum & 0xFFFF) + (sum >> 16);
// Return the one's complement of sum //
return ( (uint16_t)(~sum) );
}
// Define some constants.
#define ETH_HDRLEN 14 // Ethernet header length
#define IP6_HDRLEN 40 // IPv6 header length
#define TCP_HDRLEN 20 // TCP header length, excludes options data
// Function prototypes
uint16_t checksum (uint16_t *, int);
uint16_t tcp6_checksum (struct ip6_hdr, struct tcphdr, uint8_t *, int);
char *allocate_strmem (int);
uint8_t *allocate_ustrmem (int);
int *allocate_intmem (int);
int
main (int argc, char **argv)
{
int i, status, frame_length, sd, bytes, *tcp_flags, opt_len;
char *interface, *target, *src_ip, *dst_ip;
struct ip6_hdr iphdr;
struct tcphdr tcphdr;
uint8_t *src_mac, *dst_mac, *ether_frame;
uint8_t *options;
struct addrinfo hints, *res;
struct sockaddr_in6 *ipv6;
struct sockaddr_ll device;
struct ifreq ifr;
void *tmp;
// Allocate memory for various arrays.
src_mac = allocate_ustrmem (6);
dst_mac = allocate_ustrmem (6);
ether_frame = allocate_ustrmem (IP_MAXPACKET);
interface = allocate_strmem (40);
target = allocate_strmem (INET6_ADDRSTRLEN);
src_ip = allocate_strmem (INET6_ADDRSTRLEN);
dst_ip = allocate_strmem (INET6_ADDRSTRLEN);
tcp_flags = allocate_intmem (8);
options = allocate_ustrmem (40);
// Interface to send packet through.
strcpy (interface, "eth0");
// Source IPv6 address: you need to fill this out
strcpy (src_ip,"1080:a2b1::1e:0");
strcpy (dst_ip,"ff00::24");
// IPv6 header
// IPv6 version (4 bits), Traffic class (8 bits), Flow label (20 bits)
iphdr.ip6_flow = htonl ((6 << 28) | (0 << 20) | 0);
// Payload length (16 bits): TCP header + TCP options
//iphdr.ip6_plen = htons (TCP_HDRLEN + opt_len);
//iphdr.ip6_plen = htons (TCP_HDRLEN);
iphdr.ip6_plen = htons(TCP_HDRLEN);
// Next header (8 bits): 6 for TCP
iphdr.ip6_nxt = IPPROTO_TCP;
// Hop limit (8 bits): default to maximum value
iphdr.ip6_hops = 128;
// Source IPv6 address (128 bits)
if ((status = inet_pton (AF_INET6, src_ip, &(iphdr.ip6_src))) != 1) {
fprintf (stderr, "inet_pton() failed.\nError message: %s", strerror (status));
exit (EXIT_FAILURE);
}
char srcAddr[32];
memset(srcAddr,0,32);
printf("src ip addr:");
ipv6_to_str_unexpanded(srcAddr,&(iphdr.ip6_src));
// Destination IPv6 address (128 bits)
if ((status = inet_pton (AF_INET6, dst_ip, &(iphdr.ip6_dst))) != 1) {
fprintf (stderr, "inet_pton() failed.\nError message: %s", strerror (status));
exit (EXIT_FAILURE);
}
char dstAddr[32];
memset(dstAddr,0,32);
printf("dst ip addr:");
ipv6_to_str_unexpanded(dstAddr,&(iphdr.ip6_dst));
// TCP header
// Source port number (16 bits)
tcphdr.th_sport = htons (1058);
printf("src port:[%d]\n",tcphdr.th_sport);
// Destination port number (16 bits)
tcphdr.th_dport = htons (80);
// Sequence number (32 bits)
tcphdr.th_seq = htonl (1);
printf("seq :[%d]\n",tcphdr.th_seq);
// Acknowledgement number (32 bits): 0 in first packet of SYN/ACK process
tcphdr.th_ack = htonl (1);
// Reserved (4 bits): should be 0
tcphdr.th_x2 = 0;
// Data offset (4 bits): size of TCP header + length of options, in 32-bit words
//tcphdr.th_off = (TCP_HDRLEN + opt_len) / 4;
tcphdr.th_off = TCP_HDRLEN/4;
// Flags (8 bits)
// FIN flag (1 bit)
tcp_flags[0] = 0;
// SYN flag (1 bit): set to 1
tcp_flags[1] = 0;
// RST flag (1 bit)
tcp_flags[2] = 1;
// PSH flag (1 bit)
tcp_flags[3] = 0;
// ACK flag (1 bit)
tcp_flags[4] = 1;
// URG flag (1 bit)
tcp_flags[5] = 0;
// ECE flag (1 bit)
tcp_flags[6] = 0;
// CWR flag (1 bit)
tcp_flags[7] = 0;
tcphdr.th_flags = 0;
for (i=0; i<8; i++) {
tcphdr.th_flags += (tcp_flags[i] << i);
}
// Window size (16 bits)
tcphdr.th_win = htons (8760);
// Urgent pointer (16 bits): 0 (only valid if URG flag is set)
tcphdr.th_urp = htons (0);
tcphdr.th_sum = 0;
//tcphdr.th_sum = get_ipv6_udptcp_checksum(&iphdr, (uint16_t *)&tcphdr);
tcphdr.th_sum = tcp_checksum((void *)&tcphdr, htons(20), iphdr.ip6_src, iphdr.ip6_dst);
printf("TCP Checksum:[%x]\n",tcphdr.th_sum);
return 0;
}
char *
allocate_strmem (int len)
{
void *tmp;
if (len <= 0) {
fprintf (stderr, "ERROR: Cannot allocate memory because len = %i in allocate_strmem().\n", len);
exit (EXIT_FAILURE);
}
tmp = (char *) malloc (len * sizeof (char));
if (tmp != NULL) {
memset (tmp, 0, len * sizeof (char));
return (tmp);
} else {
fprintf (stderr, "ERROR: Cannot allocate memory for array allocate_strmem().\n");
exit (EXIT_FAILURE);
}
}
