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Handle weird 3-way handshake(syn&ack -> syn -> ack)

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I have pcaps from Cisco2960 span port and found some tcp handshake has weird order 3-way handshake.
It seems first packet order between sessions is not guaranted for cisco span. maybe.
Current state transition is
        INIT -- syn --> SYN1 -- syn&ack --> SYN2 -- ack --> ESTABLISHED
New state transition starts with SYN1 or SYN2 and adds(revive actually)
STATE_ACK to handle both cases.
case1 : INIT -- syn --> SYN1 -- syn&ack -->ACK -- ack --> ESTABLISHED (normal)
case2 : INIT -- syn&ack --> SYN2 -- syn -->ACK -- ack --> ESTABLISHED
(weird)
This commit is contained in:
EaseTheWorld 2019-08-14 09:00:54 +09:00
parent 85c1e2a4fe
commit 36d81fabcb
1 changed files with 34 additions and 21 deletions
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39
base/tcppack.c
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@ -91,18 +91,13 @@ int process_tcp_packet(handler,ctx,p)
if(r!=R_NOT_FOUND)
ABORT(r);
/*Note that we MUST receive the 3-way handshake in the
proper order. This shouldn't be a problem, though,
except for simultaneous connects*/
if((p->tcp->th_flags & (TH_SYN|TH_ACK))!=TH_SYN){
if((p->tcp->th_flags & TH_SYN)!=TH_SYN){
DBG((0,"TCP: rejecting packet from unknown connection, seq: %u\n",ntohl(p->tcp->th_seq)));
return(0);
}
DBG((0,"SYN1 seq: %u",ntohl(p->tcp->th_seq)));
if(r=new_connection(handler,ctx,p,&conn))
ABORT(r);
conn->i2r.seq=ntohl(p->tcp->th_seq)+1;
return(0);
}
@ -112,16 +107,22 @@ int process_tcp_packet(handler,ctx,p)
switch(conn->state){
case TCP_STATE_SYN1:
if(direction != DIR_R2I)
break;
if((p->tcp->th_flags & (TH_SYN|TH_ACK))!=(TH_SYN|TH_ACK))
break;
if(direction == DIR_R2I && (p->tcp->th_flags & TH_SYN)) {
DBG((0,"SYN2 seq: %u",ntohl(p->tcp->th_seq)));
conn->r2i.seq=ntohl(p->tcp->th_seq)+1;
conn->r2i.ack=ntohl(p->tcp->th_ack)+1;
conn->state=TCP_STATE_SYN2;
DBG((0,"SYN2 seq: %u",ntohl(p->tcp->th_seq)));
conn->state=TCP_STATE_ACK;
}
break;
case TCP_STATE_SYN2:
if(direction == DIR_I2R && (p->tcp->th_flags & TH_SYN)) {
DBG((0,"SYN1 seq: %u",ntohl(p->tcp->th_seq)));
conn->i2r.seq=ntohl(p->tcp->th_seq)+1;
conn->i2r.ack=ntohl(p->tcp->th_ack)+1;
conn->state=TCP_STATE_ACK;
}
break;
case TCP_STATE_ACK:
{
char *sn=0,*dn=0;
if(direction != DIR_I2R)
@ -178,11 +179,23 @@ static int new_connection(handler,ctx,p,connp)
int r,_status;
tcp_conn *conn=0;
if ((p->tcp->th_flags & (TH_SYN|TH_ACK))==TH_SYN) {
if(r=tcp_create_conn(&conn,&p->ip->ip_src,ntohs(p->tcp->th_sport),
&p->ip->ip_dst,ntohs(p->tcp->th_dport)))
ABORT(r);
DBG((0,"SYN1 seq: %u",ntohl(p->tcp->th_seq)));
conn->i2r.seq=ntohl(p->tcp->th_seq)+1;
conn->i2r.ack=ntohl(p->tcp->th_ack)+1;
conn->state=TCP_STATE_SYN1;
} else { // SYN&ACK comes first somehow
if(r=tcp_create_conn(&conn,&p->ip->ip_dst,ntohs(p->tcp->th_dport),
&p->ip->ip_src,ntohs(p->tcp->th_sport)))
ABORT(r);
DBG((0,"SYN2 seq: %u",ntohl(p->tcp->th_seq)));
conn->r2i.seq=ntohl(p->tcp->th_seq)+1;
conn->r2i.ack=ntohl(p->tcp->th_ack)+1;
conn->state=TCP_STATE_SYN2;
}
memcpy(&conn->start_time,&p->ts,sizeof(struct timeval));
memcpy(&conn->last_seen_time,&p->ts,sizeof(struct timeval));
if(r=create_proto_handler(handler,ctx,&conn->analyzer,conn,&p->ts))