原始碼編譯方法：gcc -o syn syn.c
結果：在centos6上成功執行，用tcpdump抓包分析，傳送的對端有syn，ack包返回，一切正常。
過程：寫**時忘記了對tcph->protocol賦值，計算出得checksum老不對，資料報是成功發出去了，但是對端沒syn,ack包回，查了幾個小時，鬱悶死我~~~
疑問：ip->check為0是核心會計算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，這是為何？標記一下，有結論再附上。
#include #include #include #include #include #include /* 資料報最大長度，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 */
/* 資料報構造引數 */
struct st_args;
/* 用於計算tcp校驗和的偽頭部 */
struct psdhdr;
/* * 採用彙編計算ip頭部校驗和
* @param[in]: iph, ip頭指標;
* @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)
/* * 計算校驗和
* @param[in]: buffer, 待計算資料指標
* @param[in]: size, 資料長度
* * @return 校驗和
* */
uint16_t csum(uint16_t *buffer, int size)
if(size)
cksum = (cksum>>16) + (cksum&0xffff);
cksum += (cksum>>16);
return (uint16_t)(~cksum);}/*
* 除錯用的函式，用於輸出資料
* */
void data_dump(uint8_t *pdata, int len)}/*
* 資料報傳送函式，只構造了ip頭+tcp頭大小的長度；
* ip頭和tcp都無選項部分，tcp無負載資料
* @param[in]: parg, 構造資料報是採用的一些引數
* * @return -1, 傳送失敗；0, 傳送成功
* */
int send_pkg(struct st_args* parg)
; uint8_t psdheader[max_psd_size] = ;
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)
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, 核心會自動計算校驗和 */
//iph->check = ip_fast_csum(datagram, iph->ihl);
if(setsockopt(sockfd, ipproto_ip, ip_hdrincl, poptval, sizeof(optval)) < 0)
ret = sendto(sockfd, datagram, iph->tot_len, 0,
(struct sockaddr*)&(parg->daddr), sizeof(parg->daddr));
if(ret < 0)
//data_dump(datagram, 40);
close(sockfd);
return 0;
err_out:
if(sockfd != -1)
close(sockfd);
return -1;
}int main(int argc, char **argv)
, ,,};
while((arg = getopt_long(argc, argv, "s:p:d:f:", lopts, null)) != -1)
}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;
}
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