/*------------------------------------------------------------------------
* tcpok - determine if a received segment is acceptable
*------------------------------------------------------------------------
*/
Bool
tcpok(struct tcb *ptcb, struct ep *pep)
{
struct ip *pip = (struct ip *)pep->ep_data;
struct tcp *ptcp = (struct tcp *) pip->ip_data;
int seglen, rwindow;
tcpseq wlast, slast, sup;
Bool rv;
if (ptcb->tcb_state < TCPS_SYNRCVD)
return TRUE;
seglen = pip->ip_len - IP_HLEN(pip) - TCP_HLEN(ptcp);
/* add SYN and FIN */
if (ptcp->tcp_code & TCPF_SYN)
++seglen;
if (ptcp->tcp_code & TCPF_FIN)
++seglen;
rwindow = ptcb->tcb_rbsize - ptcb->tcb_rbcount;
if (rwindow == 0 && seglen == 0)
return ptcp->tcp_seq == ptcb->tcb_rnext;
wlast = ptcb->tcb_rnext + rwindow - 1;
rv = (ptcp->tcp_seq - ptcb->tcb_rnext) >= 0 &&
(ptcp->tcp_seq - wlast) <= 0;
if (seglen == 0)
return rv;
slast = ptcp->tcp_seq + seglen - 1;
rv |= (slast - ptcb->tcb_rnext) >= 0 && (slast - wlast) <= 0;
/* If no window, strip data but keep ACK, RST and URG */
if (rwindow == 0)
pip->ip_len = IP_HLEN(pip) + TCP_HLEN(ptcp);
return rv;
}
/*------------------------------------------------------------------------
* tcpreset - generate a reset in response to a bad packet
*------------------------------------------------------------------------
*/
int
tcpreset(struct ep *pepin)
{
struct ep *pepout;
struct ip *pipin = (struct ip *)pepin->ep_data, *pipout;
struct tcp *ptcpin = (struct tcp *)pipin->ip_data, *ptcpout;
int datalen;
if (ptcpin->tcp_code & TCPF_RST)
return OK; /* no RESETs on RESETs */
pepout = (struct ep *)getbuf(Net.netpool);
if ((int)pepout == SYSERR)
return SYSERR;
pipout = (struct ip *)pepout->ep_data;
pipout->ip_src = pipin->ip_dst;
pipout->ip_dst = pipin->ip_src;
ptcpout = (struct tcp *)pipout->ip_data;
ptcpout->tcp_sport = ptcpin->tcp_dport;
ptcpout->tcp_dport = ptcpin->tcp_sport;
if (ptcpin->tcp_code & TCPF_ACK) {
ptcpout->tcp_seq = ptcpin->tcp_ack;
ptcpout->tcp_code = TCPF_RST;
} else {
ptcpout->tcp_seq = 0;
ptcpout->tcp_code = TCPF_RST|TCPF_ACK;
}
datalen = pipin->ip_len - IP_HLEN(pipin) - TCP_HLEN(ptcpin);
if (ptcpin->tcp_code & TCPF_SYN)
datalen++;
if (ptcpin->tcp_code & TCPF_FIN)
datalen++;
ptcpout->tcp_ack = ptcpin->tcp_seq + datalen;
ptcpout->tcp_offset = TCPHOFFSET;
ptcpout->tcp_window = ptcpout->tcp_urgptr = 0;
tcph2net(ptcpout);
ptcpout->tcp_cksum = 0;
ptcpout->tcp_cksum = tcpcksum(pepout, TCPMHLEN);
TcpOutSegs++;
TcpOutRsts++;
return ipsend(pipin->ip_src, pepout, TCPMHLEN, IPT_TCP,
IPP_NORMAL, IP_TTL);
}
/*------------------------------------------------------------------------
* tcpackit - generate an ACK for a received TCP packet
*------------------------------------------------------------------------
*/
int
tcpackit(struct tcb *ptcb, struct ep *pepin)
{
struct ep *pepout;
struct ip *pipin = (struct ip *)pepin->ep_data, *pipout;
struct tcp *ptcpin = (struct tcp *)pipin->ip_data, *ptcpout;
if (ptcpin->tcp_code & TCPF_RST)
return OK;
if (pipin->ip_len <= IP_HLEN(pipin) + TCP_HLEN(ptcpin) &&
!(ptcpin->tcp_code & (TCPF_SYN|TCPF_FIN)))
return OK; /* duplicate ACK */
pepout = (struct ep *)getbuf(Net.netpool);
if ((int)pepout == SYSERR)
return SYSERR;
pepout->ep_order = ~0;
pipout = (struct ip *)pepout->ep_data;
pipout->ip_src = pipin->ip_dst;
pipout->ip_dst = pipin->ip_src;
ptcpout = (struct tcp *)pipout->ip_data;
ptcpout->tcp_sport = ptcpin->tcp_dport;
ptcpout->tcp_dport = ptcpin->tcp_sport;
ptcpout->tcp_seq = ptcb->tcb_snext;
ptcpout->tcp_ack = ptcb->tcb_rnext;
ptcpout->tcp_code = TCPF_ACK;
ptcpout->tcp_offset = TCPHOFFSET;
ptcpout->tcp_window = tcprwindow(ptcb);
ptcpout->tcp_urgptr = 0;
ptcpout->tcp_cksum = 0;
tcph2net(ptcpout);
pepout->ep_order &= ~EPO_TCP;
ptcpout->tcp_cksum = tcpcksum(pepout, TCPMHLEN);
TcpOutSegs++;
return ipsend(pipin->ip_src, pepout, TCPMHLEN, IPT_TCP,
IPP_NORMAL, IP_TTL);
}
