TCP 序列号的简单递增并将其分配给发送 tcp header Z012570F8387D14D 中的确认号
[英]simple incrementing of TCP sequence number and assigning it to sending tcp header acknowledgement number in C
问题描述
我正在模拟 TCP，现在我只能处理确认号。
tcph->seq是接收到的序列号，我将它分配给 tcp->ack_seq 这是确认号，如
tcp->ack_seq=htons(ntohs(tcph->seq)+1);
但是考虑到上面的代码，似乎有一些本质上的错误，tcph->seq 和 tcph 是网络字节顺序，这应该是因为我从缓冲区中转换它并分配给 tcph 指针
这是我的简单线程 function 读取接收到的缓冲区提取 tcthdr (struct tcph) 并调整值或分配值以发送 tcphdr (struct tcp)
它只是做了它所做的我确实有问题。 我不断收到错误的确认号（并没有真正反映我如何增加序列号并将其分配给确认号）。 任何人都可以看看这个，所以我终于有 TCP 握手成功。 问题来了，我发送 SYN+ACK 数据包，我的客户端重新传输 SYN 数据包，这个循环污染了我的 wireshark 视图没有什么有用的，只是 SYN 的大量战利品并从我的代码中响应 SYN+ACK
void * receiver(void *data)
{
//struct sockaddr_in cliaddr = {0};
int recvlen = -1;
int writelen = -1;
//socklen_t clilen = sizeof(cliaddr);
while (!_do_exit)
{
//recvlen = rrecvfrom(_udp_fd, buf, sizeof(buf), 0, (struct sockaddr*)&cliaddr, &clilen);
char buf[VPN_MAX_MTU] = {0};
char buf_1[VPN_MAX_MTU] = {0};
memset(buf,0,VPN_MAX_MTU);
memset(buf_1,0,VPN_MAX_MTU);
memset(buf,0,VPN_MAX_MTU);
memset(buf_1,0,VPN_MAX_MTU);
char *str_source=malloc(18);
char *str_dest=malloc(18);
memset(str_source,0,18);
memset(str_dest,0,18);
recvlen=read(_tun_fd,buf,VPN_MAX_MTU);
if(recvlen>0)
{
//BUFFER received here
struct iphdr *iph=(struct iphdr *)buf;
struct iphdr *ip=(struct iphdr *)buf_1;
int y=0;
for(int b=0;b<(sizeof(struct iphdr)+sizeof(struct tcphdr));b++)
{
if(y==20)
{
y=0;
//printf("\n");
}
//printf("%x ",buf[b]<<24);
y++;
}
// tcph->check=(tcp_chksum(iph,tcph));
//iph->check = csum(iph, sizeof(*iph));
char str_src[18]={0};
char str_dest_t[18]={0};
//printf("IN %s %s\n",get_ip_str_1(iph->saddr,str_src),get_ip_str_1(iph->daddr,str_dest_t));
memcpy(&ip->daddr,&iph->saddr,sizeof(uint32_t));
memcpy(&ip->saddr,&iph->daddr,sizeof(uint32_t));
//printf("OUT %s %s\n",get_ip_str_1(ip->saddr,str_src),get_ip_str_1(ip->daddr,str_dest_t));
//Create ip
//DOUBLE CHECK FOR BYTE ORDER
//ip->tot_len=iph->tot_len;
populate_ip_some(iph,ip);
ip->tos=0;
ip->tos=iph->tos;
ip->ihl = 5;
ip->version = 4;
ip->tot_len = htons(sizeof(struct iphdr) + sizeof(struct tcphdr));
ip->protocol = 6;
ip->check=0;
//DOUBLE CHECK FOR BYTE ORDER
ip->id=htons(100);
ip->check = htons(csum(ip, sizeof(*ip)));
//printf("before %d \n",htons(iph->check));
iph->check=0;
//printf("middle %d\n",iph->check);
//DOUBLE CHECK FOR BYTE ORDER
iph->check = htons(csum(iph, sizeof(*iph)));
int i=iph->ihl*4;
struct tcphdr *tcph=(struct tcphdr *)(buf+i);
//printf("tcp before %x\n",htons(tcph->check));
tcph->check=0;
printf("TCP START\n");
tcph->check=(tcp_chksum(iph,tcph));
printf("TCP END\n");
//printf("tcp after %d\n",(tcph->check));
//printf("i == %d\n",i);
//POSSIBLY PRINT IPH for fun
//for(int a=0;a<recvlen;a++)
//printf("%x\n",buf[a]);
//GET ihl SEND -- tcp
int j=(ip->ihl*4);
//printf("j == %d\n",j);
int x=0;
//SEEK filling
struct tcphdr *tcp=(struct tcphdr *)(buf_1+20);
//populate_tcp_some(tcph,tcp);//Do LOOK AT THIS FUNCTION TO [SEE/CORRECT IT] >:)
seq++;
if(tcph->syn==1)
{
printf("WHAT THE HELL THEN WHY\n");
printf("syn\n");
//populate_tcp_some(tcph,tcp);
tcp->seq=htons(seq);
//tcp->ack_seq=htons(ntohs(tcph->seq)+1);
printf("seq = %d | ack_seq = %d\n",ntohs(tcph->seq),ntohs(tcp->ack_seq));
tcp->syn=1;
tcp->ack=1;
tcp->res1=0;
tcp->res1=0;
tcp->urg=0;
tcp->psh=0;
tcp->fin=0;
tcp->doff=5;
tcp->source=htons(80);
tcp->dest=tcph->source;
tcp->ack_seq=htons(ntohs(tcph->seq)+1);//htons(ntohs(tcph->seq)+1);
// printf("received tcp syn = %d\n",tcph->syn);
}
else if(tcph->syn==0 && tcph->ack==1){
printf("WHAT THE HELL THEN COOL\n");
printf("syn\n");
// populate_tcp_some(tcph,tcp);
//tcp->seq=htons(1);
tcp->seq=htons(seq);
tcp->ack_seq=tcph->seq;
tcp->syn=0;
tcp->ack=1;
tcp->res1=0;
tcp->res1=0;
tcp->urg=0;
tcp->psh=0;
tcp->fin=0;
tcp->doff=5;
tcp->source=htons(80);
tcp->dest=tcph->source;
//tcp->ack_seq=tcph->seq;//htons(ntohs(tcph->seq)+1);
tcp->ack_seq=htons(ntohs(tcph->seq)+1);
}
else
{
populate_tcp_some(tcph,tcp);
tcp->syn=0;
tcp->ack=1;
//tcp->seq=htons(1);
tcp->seq=htons(seq);
tcp->res1=0;
tcp->res1=0;
tcp->urg=0;
tcp->psh=0;
tcp->fin=0;
tcp->doff=5;
tcp->source=htons(80);
tcp->dest=tcph->source;
tcp->ack_seq=htons(ntohs(tcph->seq)+1);//tcp->ack_seq=tcph->seq;//htons(ntohs(tcph->seq)+1);
// printf("sending tcp syn = %d ack = %d\n",tcp->syn,tcp->ack);
}
printf("syn=%d | ack = %d | fin = %d | %d seq = %d ack_seq = %d | urg = %d | doff = %d | psh = %d rst = %d | rst2 = %d\n",tcp->syn,tcp->ack,tcp->fin,tcp->seq,tcp->ack_seq,tcp->urg,tcp->doff,tcp->psh,tcp->res1,tcp->res2);
//populate_tcp_some(tcph,tcp);
tcp->dest=tcph->source;
tcp->window=tcph->window;
//
//printf("%d %d SOURCE PORT \n",ntohs(tcph->source),ntohs(tcp->dest));
tcp->source=htons(80);
printf("%d %d PORTS \n",ntohs(tcp->source),ntohs(tcp->dest));
tcp->check=0;
//TCP CHECKSUM ABOUT TRIPPLE WOW
tcp->check=htons(tcp_chksum(ip,tcp));
//printf("tcpH = %d | tcp = %d\n",tcph->check,htons(tcp->check));
//IF needed make payload data
//WRITE
if (recvlen > 0)
{
printf("\n-WOW WOW WOW received seq = %d ack == %d",ntohs(tcph->seq),ntohs(tcp->ack_seq));
writelen = write(_tun_fd, buf_1, sizeof(struct iphdr)+sizeof(struct tcphdr));
//exit(0);
// sleep(2);
//debug("SR:%04d\n", recvlen);
//debug("TW:%04d\n", writelen);
if (writelen < 0)
{
//debug("%s: rwrite() %s [%d]\n", _progname, strerror(errno), errno);
//break;//NO NEED
}
}
else if (recvlen < 0)
{
//debug("%s: rrecvfrom() %s\n", _progname, strerror(errno));
//break;//NO NEED
}
else if (recvlen == 0)
{
//why
}
//FINALLY THEN SEND || DO WIRE SHARK
}
// ...:)__ :) __:) ___:)___ (: __(:__ (;...
}
debug("** Receiver ending.\n");
pthread_exit(NULL);
}
更新
现在我得到 TCP 最后一个段没有为我的 ACK+SYN 数据包捕获
这是收到的 SYN
0000 45 00 00 3c c5 18 40 00 40 06 e0 2f c0 a8 0a 14
0010 c0 a8 0a 0f bc b2 00 50 f0 32 1f de 00 00 00 00
0020 a0 02 fa f0 c6 93 00 00 02 04 05 b4 04 02 08 0a
0030 95 a6 8e 4d 00 00 00 00 01 03 03 07
这是 SYN+ACK
0000 45 00 00 28 00 64 40 00 40 06 a4 f8 c0 a8 0a 0f
0010 c0 a8 0a 14 00 50 bc b2 86 e8 00 00 f0 32 1f df
0020 50 12 fa f0 cb 70 00 00
这是 SYN AGAIN
0000 45 00 00 3c c5 19 40 00 40 06 e0 2e c0 a8 0a 14
0010 c0 a8 0a 0f bc b2 00 50 f0 32 1f de 00 00 00 00
0020 a0 02 fa f0 c2 9c 00 00 02 04 05 b4 04 02 08 0a
0030 95 a6 92 44 00 00 00 00 01 03 03 07
在此数据包的行中再次 SYN 我收到消息最后一个段未捕获
0000 45 00 00 28 00 64 40 00 40 06 a4 f8 c0 a8 0a 0f
0010 c0 a8 0a 14 00 50 bc b2 86 e9 00 00 f0 32 1f df
0020 50 12 fa f0 cb 6f 00 00
这是我的更新 2
同步
0000 45 00 00 3c 9f 75 40 00 40 06 05 d3 c0 a8 0a 14
0010 c0 a8 0a 0f bc b8 00 50 55 a8 f4 2c 00 00 00 00
0020 a0 02 fa f0 83 25 00 00 02 04 05 b4 04 02 08 0a
0030 96 60 97 37 00 00 00 00 01 03 03 07
同步 + 确认
0000 45 00 00 28 00 64 40 00 40 06 a4 f8 c0 a8 0a 0f
0010 c0 a8 0a 14 00 50 bc b8 00 00 00 03 55 a8 f4 2d
0020 50 12 fa f0 18 8c 00 00
这是 SYN agian retramit
0000 45 00 00 3c 9f 76 40 00 40 06 05 d2 c0 a8 0a 14
0010 c0 a8 0a 0f bc b8 00 50 55 a8 f4 2c 00 00 00 00
0020 a0 02 fa f0 7f 38 00 00 02 04 05 b4 04 02 08 0a
0030 96 60 9b 24 00 00 00 00 01 03 03 07
1 个解决方案
解决方案1
1 已采纳 2022-01-01 09:24:18
序列号和确认号是 32 位值：
因此这一行：
tcp->ack_seq=htons(ntohs(tcph->seq)+1);//htons(ntohs(tcph->seq)+1);
正在使用 htons/ntohs，它们是交换 16 位整数字节的函数。 您需要将其更改为使用htonl和ntohl
这可能不是你唯一的错误。
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