Checksum Computation!!
[ltp2tcp] / encap.c
diff --git a/encap.c b/encap.c
index 2f08235931d94854adc8663a8859d3a8b83def2d..c841ba29e5d76098a67f3bf2b26af1626a22b4a4 100644 (file)
--- a/encap.c
+++ b/encap.c
@@ -28,6 +28,7 @@ Notes:
        2)Uses some special types from Linux (u_char, u_int32_t)
 ******************************************************************************/
 #include "ltp2tcp.h"
+#include "checksums.h"
 
 
 
@@ -74,6 +75,7 @@ int fill_eip4_encap(struct eip4_en_p *eip, const u_char* data, int dlen, struct
 /* encapsulation manipulation after conversion */
 int eip4_post(struct eip4_en_p *eip, int tlen, u_char* data){
        struct iphdr *iph;
+       struct tcphdr *tcph;
 
        /* Move data pointer to start of IPv4 header*/
        data+=sizeof(struct ether_header);
@@ -86,7 +88,17 @@ int eip4_post(struct eip4_en_p *eip, int tlen, u_char* data){
 
        /*Adjust IPv4 header to account for packet's total length*/
        iph=(struct iphdr*)data;
-       iph->tot_len=htons(sizeof(struct iphdr)+tlen);
+       iph->tot_len=htons(iph->ihl*4+tlen);
+
+       /*Compute IPv4 Checksum*/
+       iph->check=0;
+       iph->check=ipv4_chksum(data,iph->ihl*4);
+
+       /*Compute TCP Checksum*/
+       data+=iph->ihl*4;
+       tcph=(struct tcphdr*)data;
+       tcph->check=0;
+       tcph->check=ipv4_pseudohdr_chksum(data, tlen, (u_char*)&iph->daddr, (u_char*)&iph->saddr, iph->protocol);
        return 0;
 }
 
@@ -135,6 +147,10 @@ int eip4_handshake(struct eip4_en_p *eip, struct pcap_pkthdr *h){
                iph->check=htonl(0);
                iph->tot_len=htons(sizeof(struct iphdr)+sizeof(struct tcphdr)+4);
 
+               /*Compute IPv4 Checksum*/
+               iph->check=0;
+               iph->check=ipv4_chksum((u_char*)iph,iph->ihl*4);
+
                /*Build TCP header*/
                ptr+=sizeof(struct ether_header)+ sizeof(struct iphdr);
                tcph=(struct tcphdr*)ptr;
@@ -161,6 +177,11 @@ int eip4_handshake(struct eip4_en_p *eip, struct pcap_pkthdr *h){
                ptr++;
                *ptr=2;
 
+               /*Compute TCP Checksum*/
+               tcph->check=0;
+               tcph->check=ipv4_pseudohdr_chksum((u_char*)tcph,tcph->doff*4,
+                                                                               (u_char*)&iph->daddr, (u_char*)&iph->saddr, iph->protocol);
+
                /*Save To Packet Capture*/
                pcap_dump((u_char*)state.out,&nh, data);
 
@@ -188,6 +209,10 @@ int eip4_handshake(struct eip4_en_p *eip, struct pcap_pkthdr *h){
                iph->daddr=temp;
                iph->tot_len=htons(sizeof(struct iphdr)+sizeof(struct tcphdr)+4);
 
+               /*Compute IPv4 Checksum*/
+               iph->check=0;
+               iph->check=ipv4_chksum((u_char*)iph,iph->ihl*4);
+
                /*Build TCP header*/
                ptr+=sizeof(struct ether_header)+ sizeof(struct iphdr);
                tcph=(struct tcphdr*)ptr;
@@ -214,6 +239,11 @@ int eip4_handshake(struct eip4_en_p *eip, struct pcap_pkthdr *h){
                ptr++;
                *ptr=2;
 
+               /*Compute TCP Checksum*/
+               tcph->check=0;
+               tcph->check=ipv4_pseudohdr_chksum((u_char*)tcph,tcph->doff*4 ,
+                                                                       (u_char*)&iph->daddr, (u_char*)&iph->saddr, iph->protocol);
+
                /*Save To Packet Capture*/
                pcap_dump((u_char*)state.out,&nh, data);
 
@@ -237,6 +267,10 @@ int eip4_handshake(struct eip4_en_p *eip, struct pcap_pkthdr *h){
                iph->check=htonl(0);
                iph->tot_len=htons(sizeof(struct iphdr)+sizeof(struct tcphdr));
 
+               /*Compute IPv4 Checksum*/
+               iph->check=0;
+               iph->check=ipv4_chksum((u_char*)iph,iph->ihl*4);
+
                /*Build TCP header*/
                ptr+=sizeof(struct ether_header)+ sizeof(struct iphdr);
                tcph=(struct tcphdr*)ptr;
@@ -257,6 +291,11 @@ int eip4_handshake(struct eip4_en_p *eip, struct pcap_pkthdr *h){
                tcph->ack_seq=htonl(state.ack_num);
                tcph->window=htons(WIN_FACTOR);
 
+               /*Compute TCP Checksum*/
+               tcph->check=0;
+               tcph->check=ipv4_pseudohdr_chksum((u_char*)tcph,tcph->doff*4,
+                                                               (u_char*)&iph->daddr, (u_char*)&iph->saddr, iph->protocol);
+
                /*Save To Packet Capture*/
                pcap_dump((u_char*)state.out,&nh, data);
        return 0;
@@ -307,6 +346,10 @@ int eip4_fin(struct eip4_en_p *eip){
                iph->check=htonl(0);
                iph->tot_len=htons(sizeof(struct iphdr)+sizeof(struct tcphdr));
 
+               /*Compute IPv4 Checksum*/
+               iph->check=0;
+               iph->check=ipv4_chksum((u_char*)iph,iph->ihl*4);
+
                /*Build TCP header*/
                ptr+=sizeof(struct ether_header)+ sizeof(struct iphdr);
                tcph=(struct tcphdr*)ptr;
@@ -330,6 +373,11 @@ int eip4_fin(struct eip4_en_p *eip){
                /*Update Sequence Number to include the fin packet in the sequence number space*/
                state.seq_num++;
 
+               /*Compute TCP Checksum*/
+               tcph->check=0;
+               tcph->check=ipv4_pseudohdr_chksum((u_char*)tcph,tcph->doff*4,
+                                                               (u_char*)&iph->daddr, (u_char*)&iph->saddr, iph->protocol);
+
                /* Save To Packet Capture*/
                pcap_dump((u_char*)state.out,&nh, data);
 
@@ -356,6 +404,10 @@ int eip4_fin(struct eip4_en_p *eip){
                iph->daddr=temp;
                iph->tot_len=htons(sizeof(struct iphdr)+sizeof(struct tcphdr));
 
+               /*Compute IPv4 Checksum*/
+               iph->check=0;
+               iph->check=ipv4_chksum((u_char*)iph,iph->ihl*4);
+
                /*Build TCP header*/
                ptr+=sizeof(struct ether_header)+ sizeof(struct iphdr);
                tcph=(struct tcphdr*)ptr;
@@ -376,6 +428,11 @@ int eip4_fin(struct eip4_en_p *eip){
                tcph->ack_seq=htonl(state.seq_num);
                tcph->window=htons(WIN_FACTOR);
 
+               /*Compute TCP Checksum*/
+               tcph->check=0;
+               tcph->check=ipv4_pseudohdr_chksum((u_char*)tcph,sizeof(struct tcphdr),
+                                                               (u_char*)&iph->daddr, (u_char*)&iph->saddr, iph->protocol);
+
                /*Save To Packet Capture*/
                pcap_dump((u_char*)state.out,&nh, data);
 
@@ -399,6 +456,10 @@ int eip4_fin(struct eip4_en_p *eip){
                iph->check=htonl(0);
                iph->tot_len=htons(sizeof(struct iphdr)+sizeof(struct tcphdr));
 
+               /*Compute IPv4 Checksum*/
+               iph->check=0;
+               iph->check=ipv4_chksum((u_char*)iph,iph->ihl*4);
+
                /*Build TCP header*/
                ptr+=sizeof(struct ether_header)+ sizeof(struct iphdr);
                tcph=(struct tcphdr*)ptr;
@@ -419,6 +480,11 @@ int eip4_fin(struct eip4_en_p *eip){
                tcph->ack_seq=htonl(state.ack_num);
                tcph->window=htons(WIN_FACTOR);
 
+               /*Compute TCP Checksum*/
+               tcph->check=0;
+               tcph->check=ipv4_pseudohdr_chksum((u_char*)tcph,tcph->doff*4,
+                                                               (u_char*)&iph->daddr, (u_char*)&iph->saddr, iph->protocol);
+
                /*Save To Packet Capture*/
                pcap_dump((u_char*)state.out,&nh, data);
        return 0;