【发布时间】：2021-12-31 09:47:07
【问题描述】：
tcph->seq 是接收到的序列号，我将其分配给 tcp->ack_seq，它是类似的确认号
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 是按网络字节顺序排列的，这应该是因为我从缓冲区中强制转换并分配给 tcph 指针
这是我的简单线程函数，它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，所以我终于成功地进行了 TCP 握手。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
现在我得到了没有为我的 ACK+SYN 数据包捕获的 TCP 最后一个段
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进行 SYN，我收到消息最后一段未捕获
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
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 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
【问题讨论】：
-
哦，不同大小的变量有不同的功能：见here
-
@Effie 你的意思是我需要对 ack_seq 和 seq 使用 ntohl 和 htonl 来接受 unsigned int
-
它是 32 位变量吗？好的。 （是的，它是 32 位变量）
-
@Effie 它的 uint32_t ack_seq;所以是的
-
欢迎来到 C 编程的美妙世界，整数变量有位长，每个位长的调用方式有 10 种不同的版本：)