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/* Sniffit Packet Discription File */
/* - by: Brecht Claerhout */
#include "sn_config.h"
#include "sn_defines.h"
#include "sn_structs.h"
#include <netinet/in.h>
extern int PROTO_HEAD;
extern char NO_CHKSUM;
/* This routine stolen from ping.c */
unsigned short in_cksum(unsigned short *addr,int len)
{
register int nleft = len; /* leave this alone.. my opinion is that the */
register unsigned short *w = addr;
/* register is needed to make it work for both */
register int sum = 0; /* BIG and LITTLE endian machines */
unsigned short answer = 0;
/* but then again, who am I to make such statement */
while (nleft > 1)
{
sum += *w++;
nleft -= 2;
}
if (nleft == 1)
{
*(unsigned char *)(&answer) = *(unsigned char *)w ;
sum += answer;
}
sum = (sum >> 16) + (sum & 0xffff);
sum += (sum >> 16);
answer = ~sum;
return(answer);
}
int unwrap_packet (unsigned char *sp, struct unwrap *unwrapped)
{
struct IP_header IPhead;
struct TCP_header TCPhead;
struct ICMP_header ICMPhead;
struct UDP_header UDPhead;
int i;
short int dummy; /* 2 bytes, important */
/*
printf("\n");
for(i=0;i<20;i++) printf("%X ",sp[i]);
printf("\n");
*/
memcpy(&IPhead,(sp+PROTO_HEAD),sizeof(struct IP_header));
/* IP header Conversion */
unwrapped->IP_len = (IPhead.verlen & 0xF) << 2;
unwrapped->TCP_len = 0; /* Reset structure NEEDED!!! */
unwrapped->UDP_len = 0;
unwrapped->DATA_len= 0;
unwrapped->FRAG_f = 0;
unwrapped->FRAG_nf = 0;
if(NO_CHKSUM == 0)
{
sp[PROTO_HEAD+10]=0; /* reset checksum to zero, Q&D way*/
sp[PROTO_HEAD+11]=0;
if(in_cksum((sp+PROTO_HEAD),unwrapped->IP_len) != IPhead.checksum)
{
#ifdef DEBUG_ONSCREEN
printf("Packet dropped... (invalid IP chksum)\n");
printf("%X %X (len %d)\n",in_cksum((sp+PROTO_HEAD),unwrapped->IP_len),IPhead.checksum,unwrapped->IP_len);
#endif
return NO_IP;
}
if(0)
{
#ifdef DEBUG_ONSCREEN
printf("Packet dropped... (invalid IP version)\n");
#endif
return NO_IP_4;
}
memcpy((sp+PROTO_HEAD),&IPhead,sizeof(struct IP_header));
/* restore orig buffer */
/* general programming rule */
}
#ifdef DEBUG_ONSCREEN
printf("IPheadlen: %d total length: %d\n", unwrapped->IP_len,
ntohs(IPhead.length));
#endif
dummy=ntohs(IPhead.flag_offset); dummy<<=3;
if( dummy!=0 ) /* we have offset */
{
unwrapped->FRAG_nf = 1;
}
dummy=ntohs(IPhead.flag_offset); dummy>>=13;
if( (dummy&IP_MF)&&(unwrapped->FRAG_nf==0) ) /* first frag */
{
unwrapped->FRAG_f = 1;
}
if(IPhead.protocol == TCP ) /* TCP */
{
if(unwrapped->FRAG_nf == 0) /* packet contains TCP header */
{
if( (ntohs(IPhead.length)-(unwrapped->IP_len))<20 )
{
if(unwrapped->FRAG_f==1)
{unwrapped->DATA_len = ntohs(IPhead.length) -
(unwrapped->IP_len);
if(unwrapped->DATA_len<0)
{unwrapped->DATA_len=0; return CORRUPT_IP;}
return TCP_FRAG_HEAD;
}
else
{return CORRUPT_IP;}
}
memcpy(&TCPhead,(sp+PROTO_HEAD+(unwrapped->IP_len)),
sizeof(struct TCP_header));
unwrapped->TCP_len = ntohs(TCPhead.offset_flag) & 0xF000;
unwrapped->TCP_len >>= 10;
unwrapped->DATA_len = ntohs(IPhead.length) -
(unwrapped->IP_len) - (unwrapped->TCP_len);
/* IP options can not cause SEGFAULT */
if(unwrapped->DATA_len<0) /* Fragmented TCP options */
{
if(unwrapped->FRAG_f==1)
{unwrapped->TCP_len=0;
unwrapped->DATA_len = ntohs(IPhead.length) -
(unwrapped->IP_len);
if(unwrapped->DATA_len<0)
{unwrapped->DATA_len=0; return CORRUPT_IP;}
return TCP_FRAG_HEAD;
}
else
{return CORRUPT_IP;}
}
}
else
{
unwrapped->DATA_len = ntohs(IPhead.length) - (unwrapped->IP_len);
if(unwrapped->DATA_len<0)
{unwrapped->DATA_len=0; return CORRUPT_IP;}
}
return TCP;
}
if(IPhead.protocol == ICMP ) /* ICMP */
{
if(unwrapped->FRAG_nf == 0) /* Should contain header */
{
if( (ntohs(IPhead.length)-(unwrapped->IP_len))<4 )
{return NOT_SUPPORTED;}; /* no handling of frag headers*/
memcpy(&ICMPhead,(sp+PROTO_HEAD+(unwrapped->IP_len)),
sizeof(struct ICMP_header));
unwrapped->ICMP_len = ICMP_HEADLENGTH;
unwrapped->DATA_len = ntohs(IPhead.length) -
(unwrapped->IP_len) - (unwrapped->ICMP_len);
if(unwrapped->DATA_len<0)
{
if(unwrapped->FRAG_f==1)
{unwrapped->TCP_len=0;
unwrapped->DATA_len = ntohs(IPhead.length) -
(unwrapped->IP_len);
if(unwrapped->DATA_len<0)
{unwrapped->DATA_len=0; return CORRUPT_IP;}
return NOT_SUPPORTED; /* don't handle fragmented ICMP */
}
else
{return CORRUPT_IP;}
}
return ICMP;
}
else
{
return NOT_SUPPORTED; /* don't handle fragmented ICMP */
}
}
if(IPhead.protocol == UDP ) /* UDP */
{
if(unwrapped->FRAG_nf == 0)
{
if( ((IPhead.length)-(unwrapped->IP_len))<8 )
{return NOT_SUPPORTED;}; /* don't handle frag. header */
memcpy(&UDPhead,(sp+PROTO_HEAD+(unwrapped->IP_len)),
sizeof(struct UDP_header));
unwrapped->UDP_len = UDP_HEADLENGTH;
unwrapped->DATA_len = ntohs(IPhead.length) -
(unwrapped->IP_len) - (unwrapped->UDP_len);
if(unwrapped->DATA_len<0)
{
if(unwrapped->FRAG_f==1)
{unwrapped->UDP_len=0;
unwrapped->DATA_len = ntohs(IPhead.length) -
(unwrapped->IP_len);
if(unwrapped->DATA_len<0)
{unwrapped->DATA_len=0; return CORRUPT_IP;}
return NOT_SUPPORTED;
} /* don't handle fragmented UDP */
else
{return CORRUPT_IP;}
}
return UDP;
}
else
{
return NOT_SUPPORTED; /* don't handle fragmented UDP */
}
}
return NOT_SUPPORTED;
}
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