Linux C raw socket TCP handsake

Я пытаюсь создать TCP-соединение с использованием сырых сокетов в C (в системе Debian), но мне трудно работать. Он отправит пакет, но я не получаю никакого ответа от сервера. Я тестировал и сравнивал пакет с пакетом, отправленным из nmap, и я не вижу никаких существенных отличий.

Вот TCP-пакет, полученный на стороне сервера, серверная сторона никогда не отправляет пакет SYN ACK (я контролирую использование Wireshark на стороне сервера)

No. Time Source Destination Protocol Length Info 75 1.893700000 192.168.1.129 192.168.1.114 TCP 74 56540→445 [SYN] Seq=0 Win=1024 Len=0 MSS=1460 SACK_PERM=1 WS=128 TSval=863195 TSecr=0 Frame 75: 74 bytes on wire (592 bits), 74 bytes captured (592 bits) on interface 0 Ethernet II, Src: Vmware_77:f0:a0 (00:0c:29:77:f0:a0), Dst: IntelCor_07:f9:e5 (e8:b1:fc:07:f9:e5) Internet Protocol Version 4, Src: 192.168.1.129 (192.168.1.129), Dst: 192.168.1.114 (192.168.1.114) Version: 4 Header Length: 20 bytes Differentiated Services Field: 0x00 (DSCP 0x00: Default; ECN: 0x00: Not-ECT (Not ECN-Capable Transport)) Total Length: 60 Identification: 0xb88d (47245) Flags: 0x00 Fragment offset: 0 Time to live: 255 Protocol: TCP (6) Header checksum: 0x7eea [validation disabled] Source: 192.168.1.129 (192.168.1.129) Destination: 192.168.1.114 (192.168.1.114) [Source GeoIP: Unknown] [Destination GeoIP: Unknown] Transmission Control Protocol, Src Port: 56540 (56540), Dst Port: 445 (445), Seq: 0, Len: 0 Source Port: 56540 (56540) Destination Port: 445 (445) [Stream index: 3] [TCP Segment Len: 0] Sequence number: 0 (relative sequence number) Acknowledgment number: 0 Header Length: 40 bytes .... 0000 0000 0010 = Flags: 0x002 (SYN) Window size value: 1024 [Calculated window size: 1024] Checksum: 0x7ff8 [validation disabled] Urgent pointer: 0 Options: (20 bytes), Maximum segment size, SACK permitted, Window scale, No-Operation (NOP), Timestamps Maximum segment size: 1460 bytes Kind: Maximum Segment Size (2) Length: 4 MSS Value: 1460 TCP SACK Permitted Option: True Kind: SACK Permitted (4) Length: 2 Window scale: 7 (multiply by 128) Kind: Window Scale (3) Length: 3 Shift count: 7 [Multiplier: 128] No-Operation (NOP) Type: 1 Timestamps: TSval 863195, TSecr 0 Kind: Time Stamp Option (8) Length: 10 Timestamp value: 863195 Timestamp echo reply: 0 0000 e8 b1 fc 07 f9 e5 00 0c 29 77 f0 a0 08 00 45 00 ........)w....E. 0010 00 3c b8 8d 00 00 ff 06 7e ea c0 a8 01 81 c0 a8 .<......~....... 0020 01 72 dc dc 01 bd db 0f 13 02 00 00 00 00 a0 02 .r.............. 0030 04 00 7f f8 00 00 02 04 05 b4 04 02 03 03 07 01 ................ 0040 08 0a 00 0d 2b db 00 00 00 00 ....+..... 

И вот мой код, я знаю, что это грязно, я просто пытаюсь научиться использовать сырые сокеты

 #include  #include  #include  #include  #include  #include  #include  #include  #include  #include  struct ipheader { unsigned char iph_ihl:4, /* Little-endian */ iph_ver:4; unsigned char iph_tos; unsigned short int iph_len; unsigned short int iph_ident; unsigned short int iph_offset:13, /* Little-endian*/ iph_flags:3; unsigned char iph_ttl; unsigned char iph_protocol; unsigned short int iph_chksum; unsigned int iph_sourceip; unsigned int iph_destip; }; struct tcpheader { u_int16_t tcph_srcport; u_int16_t tcph_destport; u_int32_t tcph_seqnum; u_int32_t tcph_acknum; u_int16_t tcph_ns:1, tcph_reserved:3, tcph_offset:4, tcph_fin:1, tcph_syn:1, tcph_rst:1, tcph_psh:1, tcph_ack:1, tcph_urg:1, tcph_ece:1, tcph_cwr:1; u_int16_t tcph_win; u_int16_t tcph_chksum; u_int16_t tcph_urgptr; }; struct tcpheaderOptions { u_int16_t tcph_mssOpt:8, tcph_mssLen:8; u_int16_t tcph_mss; u_int16_t tcph_sack:8, tcph_sackLen:8; u_int16_t tcph_winOpt:8, tcph_winLen:8; u_int32_t tcph_win:8, tcph_winNOP:8, tcph_timeOpt:8, tcph_timeLen:8; u_int32_t tcph_time; u_int32_t tcph_timeEcho; }; unsigned short /* this function generates header checksums */ csum (unsigned short *buf, int nwords) { unsigned long sum; for (sum = 0; nwords > 0; nwords--) sum += *buf++; sum = (sum >> 16) + (sum & 0xffff); sum += (sum >> 16); return ~sum; } int main(void) { char datagram[4096]; char data[] = "Hello my name is Keith, this is my first packet"; memset(datagram,0,4096); struct ipheader *IPInfo = (struct ipheader *) datagram; struct tcpheader *TCPHeader = (struct tcpheader *) (datagram + sizeof(struct ipheader)); struct tcpheaderOptions *TCPOptions = (struct tcpheaderOptions *) (datagram + sizeof(struct tcpheader) + sizeof(struct ipheader)); struct sockaddr_in sin; //Te destination sin.sin_family = AF_INET; sin.sin_port = htons(4); sin.sin_addr.s_addr = inet_addr("192.168.1.114"); IPInfo->iph_ver = 4; //What IP version are we using? v4 IPInfo->iph_ihl = 5; //The IP header size in bytes IPInfo->iph_tos = 0; //The IP header type of service 0x00 is normal IPInfo->iph_len = sizeof(struct ipheader) + sizeof(struct tcpheader) + sizeof(struct tcpheaderOptions); //The IP length of the IP datagram IPInfo->iph_ident = htonl(54321); //The IP header ID (used when fragmented) IPInfo->iph_offset = 0; //IP fragment offset IPInfo->iph_ttl = 255; //The IP TTL IPInfo->iph_protocol = 6; //The transport layer protocol (6 for TCP, 1 for ICMP, 17 for UDP) IPInfo->iph_chksum = 0; //Checksum IPInfo->iph_sourceip = inet_addr("192.168.1.129"); //source // IPInfo->iph_destip = sin.sin_addr.s_addr; IPInfo->iph_destip = inet_addr("192.168.1.114"); char source[20]; char dest[20]; inet_ntop(AF_INET, &(IPInfo->iph_sourceip), source, 20); inet_ntop(AF_INET, &(IPInfo->iph_destip), dest, 20); printf("Source: %s\n", source); printf("Dest: %s\n", dest); //IPInfo->ip_dst.s_addr = inet_addr("192.168.1.114"); TCPHeader->tcph_srcport = htons(56540); //The source port TCPHeader->tcph_destport = htons(445); //The destination port srand(time(NULL)); TCPHeader->tcph_seqnum = rand(); //the sequence number TCPHeader->tcph_acknum = 0; //ACK packet TCPHeader->tcph_reserved = 0; //Not used TCPHeader->tcph_offset = 10; // TCPHeader->tcph_cwr = 0; TCPHeader->tcph_ns = 0; TCPHeader->tcph_syn = 1; TCPHeader->tcph_rst = 0; TCPHeader->tcph_psh = 0; TCPHeader->tcph_ack = 0; TCPHeader->tcph_urg = 0; TCPHeader->tcph_ece = 0; TCPHeader->tcph_cwr = 0; TCPHeader->tcph_ns = 0; TCPHeader->tcph_win = htons(1024); TCPHeader->tcph_chksum = 0; TCPHeader->tcph_urgptr = 0; TCPOptions->tcph_mssOpt = 2; TCPOptions->tcph_mssLen = 4; TCPOptions->tcph_winOpt = 3; TCPOptions->tcph_winLen = 3; TCPOptions->tcph_sack = 4; TCPOptions->tcph_sackLen = 2; TCPOptions->tcph_win = 7; TCPOptions->tcph_winNOP = 1; TCPOptions->tcph_mss = htons(1460); TCPOptions->tcph_timeOpt = 8; TCPOptions->tcph_timeLen = 10; TCPOptions->tcph_time = 0xdb2b0d00; //Adding the data //strcpy(datagram + sizeof(struct ipheader) + sizeof(struct tcpheader),data); TCPHeader->tcph_chksum = csum((unsigned short *) datagram,TCPHeader->tcph_offset >> 1); IPInfo->iph_chksum = csum((unsigned short *) datagram, IPInfo->iph_len >> 1); int sockfd = socket(PF_INET, SOCK_RAW, IPPROTO_TCP); if(sockfd == -1) { perror("sockfd"); exit(1); } //Setting IP_HDRINCL so that the system doesnt add headers to my packets { int one = 1; const int *val = &one; if(setsockopt(sockfd,IPPROTO_IP, IP_HDRINCL, val, sizeof(one)) iph_len, 0, (struct sockaddr *) &sin, sizeof (sin)) tcph_seqnum); //Now we will wait to receive a message back memset(datagram,0,4096); int results = recv(sockfd,datagram,sizeof(datagram),0); printf("Results: %d\n",results); IPInfo = (struct ipheader *) datagram; TCPHeader = (struct tcpheader * ) (datagram + (IPInfo->iph_ihl * 4)); printf("Packet: IPInfo->iph_ihl %d\n",IPInfo->iph_ihl); printf("ACK num = %d\n",TCPHeader->tcph_ack); char source1[20]; char dest1[20]; inet_ntop(AF_INET, &(IPInfo->iph_sourceip), source, 20); inet_ntop(AF_INET, &(IPInfo->iph_destip), dest, 20); printf("Source: %s\n",source1); printf("Dest: %s\n",dest1); printf("Size of ipheader %d\n",sizeof(struct ipheader)); printf("size of tcpheader %d\n",sizeof(struct tcpheader)); return 0; } 

Включить проверку контрольной суммы в wirehark, поэтому вы, по крайней мере, уверены, что не вычисляете неправильные контрольные суммы (в заголовке IP или TCP) – nos

Спасибо, моя контрольная сумма TCP недействительна – Keith