結果：在centos6上成功運行，用tcpdump抓包分析，發送的對端有syn，ack包返回，一切正常。
過程：寫代碼時忘記了對tcph->protocol賦值，計算出得checksum老不對，數據包是成功發出去了，但是對端沒syn,ack包回，查了幾個小時，鬱悶死我~~~
疑問：ip->check爲0是內核會計算ip頭的checksum，但是計算出得結果和我用ip_fast_csum得到的結果不一致，這是爲何？標記一下，有結論再附上。
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <getopt.h>
#include <netinet/ip.h>
#include <netinet/tcp.h>
/* 數據包最大長度，無負載 */
#define MAX_PKG_SIZE 80 /* ip header = 20 ~ 40, tcp header = 20 ~ 40; max = 80 */
/* 計算TCP校驗和的最大使用長度 */
#define MAX_PSD_SIZE 52 /* psd header = 12, tcp header = 20 ~ 40; max = 52 */
/* 數據包構造參數 */
struct st_args{
struct sockaddr_in saddr; /* 源地址 */
struct sockaddr_in daddr; /* 目的地址 */
};
/* 用於計算TCP校驗和的僞頭部 */
struct psdhdr{
uint32_t saddr; /* ip頭部源地址 */
uint32_t daddr; /* ip頭部目的地址 */
uint8_t mbz; /* 補全字段，需爲0 */
uint8_t protocol; /* ip頭部協議 */
uint16_t tcpl; /* tcp長度，包括頭部和數據部分 */
};
/*
* 採用彙編計算ip頭部校驗和
* @param[in]: iph, ip頭指針;
* @param[in]: ihl, ip頭長度(4的倍數)
*
* @return 16位校驗和
* */
static inline uint16_t ip_fast_csum(const void *iph, unsigned int ihl)
{
unsigned int sum;
asm(" movl (%1), %0\n"
" subl $4, %2\n"
" jbe 2f\n"
" addl 4(%1), %0\n"
" adcl 8(%1), %0\n"
" adcl 12(%1), %0\n"
"1: adcl 16(%1), %0\n"
" lea 4(%1), %1\n"
" decl %2\n"
" jne 1b\n"
" adcl $0, %0\n"
" movl %0, %2\n"
" shrl $16, %0\n"
" addw %w2, %w0\n"
" adcl $0, %0\n"
" notl %0\n"
"2:"
/* Since the input registers which are loaded with iph and ihl
are modified, we must also specify them as outputs, or gcc
will assume they contain their original values. */
: "=r" (sum), "=r" (iph), "=r" (ihl)
: "1" (iph), "2" (ihl)
: "memory");
return (uint16_t)sum;
}
/*
* 計算校驗和
* @param[in]: buffer, 待計算數據指針
* @param[in]: size, 數據長度
*
* @return 校驗和
* */
uint16_t csum(uint16_t *buffer, int size)
{
unsigned long cksum = 0;
while(size>1)
{
cksum += *buffer++;
size -= sizeof(uint16_t);
}
if(size)
{
cksum += *(unsigned char*)buffer;
}
cksum = (cksum>>16) + (cksum&0xffff);
cksum += (cksum>>16);
return (uint16_t)(~cksum);
}
/*
* 調試用的函數，用於輸出數據
* */
void data_dump(uint8_t *pdata, int len)
{
int i = 0;
printf("len = %d\n", len);
for(i = 0; i < len; ++i)
{
printf("%02X ", *(pdata + i));
if((i + 1) % 4 == 0)
printf("\n");
}
}
/*
* 數據包發送函數，只構造了ip頭+tcp頭大小的長度；
* ip頭和tcp都無選項部分，tcp無負載數據
* @param[in]: parg, 構造數據包是採用的一些參數
*
* @return -1, 發送失敗；0, 發送成功
* */
int send_pkg(struct st_args* parg)
{
uint8_t datagram[MAX_PKG_SIZE] = {0};
uint8_t psdheader[MAX_PSD_SIZE] = {0};
struct iphdr *iph = (struct iphdr*)datagram;
struct tcphdr *tcph = (struct tcphdr*)(datagram + sizeof(struct iphdr));
struct tcp_options *tcpopt = (struct tcp_options*)(datagram + sizeof(struct iphdr)
+ sizeof(struct tcphdr));
struct psdhdr *psdh = (struct psdhdr*)psdheader;
struct tcphdr *tcph_psd = (struct tcphdr*)(psdheader + sizeof(struct psdhdr));
int sockfd = -1, ret = 0;
int optval = 1;
const int *poptval = &optval;
sockfd = socket(PF_INET, SOCK_RAW, IPPROTO_TCP);
if(sockfd < 0)
{
perror("create socket failed!\n");
goto err_out;
}
iph->ihl = 5; /* header length, 5 * 4 = 20 Bytes */
iph->version = 4; /* version, ipv4 */
iph->tos = 0; /* type of service, gernarel */
iph->tot_len = sizeof(struct iphdr) + sizeof(struct tcphdr); /* total length, iph + tcph = 32 Bytes */
iph->id = htons(54321); /* identifcation */
iph->frag_off = htons(0x02 << 13); /* fragment offset field */
iph->ttl = 64; /* time to live */
iph->protocol = 6; /* protocol, tcp */
iph->check = 0; /* checksum */
iph->saddr = parg->saddr.sin_addr.s_addr; /* source address */
iph->daddr = parg->daddr.sin_addr.s_addr; /* dest address */
tcph->source = parg->saddr.sin_port; /* source port */
tcph->dest = parg->daddr.sin_port; /* dest port */
tcph->seq = random(); /* current sended packet sequence number */
tcph->ack_seq = 0; /* expect received next packet sequence number */
tcph->doff = sizeof(struct tcphdr) / 4; /* data position in the packet */
tcph->syn = 1; /* syn packet */
tcph->window = htons(65535); /* size of tcp window, FreeBSD uses this value */
tcph->check = 0; /* checksum */
tcph->urg_ptr = 0; /* urgent data position */
psdh->saddr = iph->saddr;
psdh->daddr = iph->daddr;
psdh->mbz = 0;
psdh->protocol = iph->protocol;
psdh->tcpl = htons(sizeof(struct tcphdr));
//data_dump(psdheader, sizeof(struct psdhdr));
memcpy(tcph_psd, tcph, sizeof(struct tcphdr));
tcph->check = csum((uint16_t*)psdheader, sizeof(struct psdhdr) + sizeof(struct tcphdr));
/* iph->check == 0時, 內核會自動計算校驗和 */
//iph->check = ip_fast_csum(datagram, iph->ihl);
if(setsockopt(sockfd, IPPROTO_IP, IP_HDRINCL, poptval, sizeof(optval)) < 0)
{
perror("setsockopt failed!");
goto err_out;
}
ret = sendto(sockfd, datagram, iph->tot_len, 0,
(struct sockaddr*)&(parg->daddr), sizeof(parg->daddr));
if(ret < 0)
{
perror("sendto socket failed!");
goto err_out;
}
//data_dump(datagram, 40);
close(sockfd);
return 0;
err_out:
if(sockfd != -1)
close(sockfd);
return -1;
}
int main(int argc, char **argv)
{
struct st_args args;
#define MAX_IP_SIZE 16
uint8_t sip[MAX_IP_SIZE] = "192.168.1.107";
uint8_t dip[MAX_IP_SIZE] = "192.168.1.1";
uint16_t sport = 55555;
uint16_t dport = 80;
int8_t arg = 0;
struct option lopts[] = {
{"saddr", required_argument, 0, 's'},
{"sport", required_argument, 0, 'p'},
{"daddr", required_argument, 0, 'd'},
{"dport", required_argument, 0, 'f'}
};
while((arg = getopt_long(argc, argv, "s:p:d:f:", lopts, NULL)) != -1)
{
switch(arg)
{
case 's':
memcpy(sip, optarg, MAX_IP_SIZE);
break;
case 'p':
sport = atoi(optarg);
break;
case 'd':
memcpy(dip, optarg, MAX_IP_SIZE);
break;
case 'f':
dport = atoi(optarg);
break;
default:
break;
}
}
memset(&args, 0, sizeof(struct st_args));
inet_pton(AF_INET, sip, (void*)&args.saddr.sin_addr);
args.saddr.sin_port = htons(sport);
inet_pton(AF_INET, dip, (void*)&args.daddr.sin_addr);
args.daddr.sin_port = htons(dport);
send_pkg(&args);
return 0;
}