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About c : TCP-socket-connect-function-ignoring-my-entirely-valid-SYNACK-packetsis-there-anything-aweful-about-that-I-cant-stop-this-send-SYN-after-SYNACK

Question Detail

I have verified in wireshark that my TCP handshake SYN+ACK packet after receiving SYN packet is getting ignored

This is wireshark main view that shows within time wireshark read my SYN+ACK packet for RTT. but my linux socket api function connect acting dummy and send SYN again, Wht I need to do in this case I am attaching my wireshark packet times plus actual communication packets, I need someone with knowledge of this and C to answer this very much thanks

This is recorded time in wireshark when packets in attempted handshake are read

This is received packet in my program code

SYN

0000   45 00 00 3c fa ed 40 00 40 06 aa 5a c0 a8 0a 14
0010   c0 a8 0a 0f bc be 00 50 f8 08 9d 5b 00 00 00 00
0020   a0 02 fa f0 bb 0f 00 00 02 04 05 b4 04 02 08 0a
0030   9a 68 0f b0 00 00 00 00 01 03 03 07

ACK SYN with valid checksums, sequence number and acknowledgement number

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 be 00 00 00 03 f8 08 9d 5c
0020   50 12 fa f0 cc f6 00 00

And this is my linux connect function complete dummy behavior by sending SYN again

0000   45 00 00 3c fa ee 40 00 40 06 aa 59 c0 a8 0a 14
0010   c0 a8 0a 0f bc be 00 50 f8 08 9d 5b 00 00 00 00
0020   a0 02 fa f0 b7 1b 00 00 02 04 05 b4 04 02 08 0a
0030   9a 68 13 a4 00 00 00 00 01 03 03 07

Can anyone please tell me how to handle this, since I am clueless on this, Is there any command that I can use to make my connect function TCP Handshake handling more attentive to my SYN+ACK packet and finally done with responding only ACK instead of playing plain stupid to send SYN again

As @LuisColorado mentioned to ask how am I generating the packet so the answer is this is how

this is my receiver thread that also transmit response TCP packets like 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] >:)
        if(tcph->syn==1)
        {
               printf("WHAT THE HELL THEN WHY\n");  
               printf("syn\n");
               populate_tcp_some(tcph,tcp);
               tcp->seq=htonl(1);
              // tcp->ack_seq=1;
               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);
               int xx=ntohl(tcph->seq)+1;
               printf("\n\nfwdfwdfwd FAWAD %x\n\n",xx);
               tcp->ack_seq=htonl(xx);
    //         printf("received tcp syn = %d\n",tcph->syn);
        }
        else
        {
               populate_tcp_some(tcph,tcp);
               tcp->syn=0;
               tcp->ack=1;
               tcp->seq=htonl(1);
               tcp->res1=0;
               tcp->res1=0;
               tcp->urg=0;
               tcp->psh=0;
               tcp->fin=0;
               tcp->doff=5;
               tcp->ack_seq=htonl(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=htons(40);//tcph->window;
        //tcp->ack_seq=tcph->seq;
        //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) 
        {
            writelen = write(_tun_fd, buf_1, sizeof(struct iphdr)+sizeof(struct tcphdr));
            //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);
}

Question Answer

No answer for now.

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