/* SPDX-License-Identifier: BSD-3-Clause */ /* * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994 * The Regents of the University of California. All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * 3. Neither the name of the University nor the names of its contributors * may be used to endorse or promote products derived from this software * without specific prior written permission. * * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. * * @(#)tcp_input.c 8.5 (Berkeley) 4/10/94 * tcp_input.c,v 1.10 1994/10/13 18:36:32 wollman Exp */ /* * Changes and additions relating to SLiRP * Copyright (c) 1995 Danny Gasparovski. */ #include "slirp.h" #include "ip_icmp.h" #define TCPREXMTTHRESH 3 #define TCP_PAWS_IDLE (24 * 24 * 60 * 60 * PR_SLOWHZ) /* for modulo comparisons of timestamps */ #define TSTMP_LT(a, b) ((int)((a) - (b)) < 0) #define TSTMP_GEQ(a, b) ((int)((a) - (b)) >= 0) /* * Insert segment ti into reassembly queue of tcp with * control block tp. Return TH_FIN if reassembly now includes * a segment with FIN. The macro form does the common case inline * (segment is the next to be received on an established connection, * and the queue is empty), avoiding linkage into and removal * from the queue and repetition of various conversions. * Set DELACK for segments received in order, but ack immediately * when segments are out of order (so fast retransmit can work). */ #define TCP_REASS(tp, ti, m, so, flags) \ { \ if ((ti)->ti_seq == (tp)->rcv_nxt && tcpfrag_list_empty(tp) && \ (tp)->t_state == TCPS_ESTABLISHED) { \ tp->t_flags |= TF_DELACK; \ (tp)->rcv_nxt += (ti)->ti_len; \ flags = (ti)->ti_flags & TH_FIN; \ if (so->so_emu) { \ if (tcp_emu((so), (m))) \ sbappend(so, (m)); \ } else \ sbappend((so), (m)); \ } else { \ (flags) = tcp_reass((tp), (ti), (m)); \ tp->t_flags |= TF_ACKNOW; \ } \ } static void tcp_dooptions(struct tcpcb *tp, uint8_t *cp, int cnt, struct tcpiphdr *ti); static void tcp_xmit_timer(register struct tcpcb *tp, int rtt); static int tcp_reass(register struct tcpcb *tp, register struct tcpiphdr *ti, struct mbuf *m) { register struct tcpiphdr *q; struct socket *so = tp->t_socket; int flags; /* * Call with ti==NULL after become established to * force pre-ESTABLISHED data up to user socket. */ if (ti == NULL) goto present; /* * Find a segment which begins after this one does. */ for (q = tcpfrag_list_first(tp); !tcpfrag_list_end(q, tp); q = tcpiphdr_next(q)) if (SEQ_GT(q->ti_seq, ti->ti_seq)) break; /* * If there is a preceding segment, it may provide some of * our data already. If so, drop the data from the incoming * segment. If it provides all of our data, drop us. */ if (!tcpfrag_list_end(tcpiphdr_prev(q), tp)) { register int i; q = tcpiphdr_prev(q); /* conversion to int (in i) handles seq wraparound */ i = q->ti_seq + q->ti_len - ti->ti_seq; if (i > 0) { if (i >= ti->ti_len) { m_free(m); /* * Try to present any queued data * at the left window edge to the user. * This is needed after the 3-WHS * completes. */ goto present; /* ??? */ } m_adj(m, i); ti->ti_len -= i; ti->ti_seq += i; } q = tcpiphdr_next(q); } ti->ti_mbuf = m; /* * While we overlap succeeding segments trim them or, * if they are completely covered, dequeue them. */ while (!tcpfrag_list_end(q, tp)) { register int i = (ti->ti_seq + ti->ti_len) - q->ti_seq; if (i <= 0) break; if (i < q->ti_len) { q->ti_seq += i; q->ti_len -= i; m_adj(q->ti_mbuf, i); break; } q = tcpiphdr_next(q); m = tcpiphdr_prev(q)->ti_mbuf; slirp_remque(tcpiphdr2qlink(tcpiphdr_prev(q))); m_free(m); } /* * Stick new segment in its place. */ slirp_insque(tcpiphdr2qlink(ti), tcpiphdr2qlink(tcpiphdr_prev(q))); present: /* * Present data to user, advancing rcv_nxt through * completed sequence space. */ if (!TCPS_HAVEESTABLISHED(tp->t_state)) return (0); ti = tcpfrag_list_first(tp); if (tcpfrag_list_end(ti, tp) || ti->ti_seq != tp->rcv_nxt) return (0); if (tp->t_state == TCPS_SYN_RECEIVED && ti->ti_len) return (0); do { tp->rcv_nxt += ti->ti_len; flags = ti->ti_flags & TH_FIN; slirp_remque(tcpiphdr2qlink(ti)); m = ti->ti_mbuf; ti = tcpiphdr_next(ti); if (so->so_state & SS_FCANTSENDMORE) m_free(m); else { if (so->so_emu) { if (tcp_emu(so, m)) sbappend(so, m); } else sbappend(so, m); } } while (ti != (struct tcpiphdr *)tp && ti->ti_seq == tp->rcv_nxt); return (flags); } /* * TCP input routine, follows pages 65-76 of the * protocol specification dated September, 1981 very closely. */ void tcp_input(struct mbuf *m, int iphlen, struct socket *inso, unsigned short af) { struct ip save_ip, *ip; struct ip6 save_ip6, *ip6; register struct tcpiphdr *ti; char *optp = NULL; int optlen = 0; int len, tlen, off; register struct tcpcb *tp = NULL; register int tiflags; struct socket *so = NULL; int todrop, acked, ourfinisacked, needoutput = 0; int iss = 0; uint32_t tiwin; int ret; struct sockaddr_storage lhost, fhost; struct sockaddr_in *lhost4, *fhost4; struct sockaddr_in6 *lhost6, *fhost6; struct gfwd_list *ex_ptr; Slirp *slirp; DEBUG_CALL("tcp_input"); DEBUG_ARG("m = %p iphlen = %2d inso = %p", m, iphlen, inso); memset(&lhost, 0, sizeof(struct sockaddr_storage)); memset(&fhost, 0, sizeof(struct sockaddr_storage)); /* * If called with m == 0, then we're continuing the connect */ if (m == NULL) { so = inso; slirp = so->slirp; /* Re-set a few variables */ tp = sototcpcb(so); m = so->so_m; so->so_m = NULL; ti = so->so_ti; tiwin = ti->ti_win; tiflags = ti->ti_flags; goto cont_conn; } slirp = m->slirp; switch (af) { case AF_INET: M_DUP_DEBUG(slirp, m, 0, sizeof(struct tcpiphdr) - sizeof(struct ip) - sizeof(struct tcphdr)); break; case AF_INET6: M_DUP_DEBUG(slirp, m, 0, sizeof(struct tcpiphdr) - sizeof(struct ip6) - sizeof(struct tcphdr)); break; } ip = mtod(m, struct ip *); ip6 = mtod(m, struct ip6 *); switch (af) { case AF_INET: if (iphlen > sizeof(struct ip)) { ip_stripoptions(m, (struct mbuf *)0); iphlen = sizeof(struct ip); } /* XXX Check if too short */ /* * Save a copy of the IP header in case we want restore it * for sending an ICMP error message in response. */ save_ip = *ip; save_ip.ip_len += iphlen; /* * Get IP and TCP header together in first mbuf. * Note: IP leaves IP header in first mbuf. */ m->m_data -= sizeof(struct tcpiphdr) - sizeof(struct ip) - sizeof(struct tcphdr); m->m_len += sizeof(struct tcpiphdr) - sizeof(struct ip) - sizeof(struct tcphdr); ti = mtod(m, struct tcpiphdr *); /* * Checksum extended TCP header and data. */ tlen = ip->ip_len; tcpiphdr2qlink(ti)->next = tcpiphdr2qlink(ti)->prev = NULL; memset(&ti->ih_mbuf, 0, sizeof(struct mbuf_ptr)); memset(&ti->ti, 0, sizeof(ti->ti)); ti->ti_x0 = 0; ti->ti_src = save_ip.ip_src; ti->ti_dst = save_ip.ip_dst; ti->ti_pr = save_ip.ip_p; ti->ti_len = htons((uint16_t)tlen); break; case AF_INET6: /* * Save a copy of the IP header in case we want restore it * for sending an ICMP error message in response. */ save_ip6 = *ip6; /* * Get IP and TCP header together in first mbuf. * Note: IP leaves IP header in first mbuf. */ m->m_data -= sizeof(struct tcpiphdr) - (sizeof(struct ip6) + sizeof(struct tcphdr)); m->m_len += sizeof(struct tcpiphdr) - (sizeof(struct ip6) + sizeof(struct tcphdr)); ti = mtod(m, struct tcpiphdr *); tlen = ip6->ip_pl; tcpiphdr2qlink(ti)->next = tcpiphdr2qlink(ti)->prev = NULL; memset(&ti->ih_mbuf, 0, sizeof(struct mbuf_ptr)); memset(&ti->ti, 0, sizeof(ti->ti)); ti->ti_x0 = 0; ti->ti_src6 = save_ip6.ip_src; ti->ti_dst6 = save_ip6.ip_dst; ti->ti_nh6 = save_ip6.ip_nh; ti->ti_len = htons((uint16_t)tlen); break; default: g_assert_not_reached(); } len = ((sizeof(struct tcpiphdr) - sizeof(struct tcphdr)) + tlen); if (cksum(m, len)) { goto drop; } /* * Check that TCP offset makes sense, * pull out TCP options and adjust length. XXX */ off = ti->ti_off << 2; if (off < sizeof(struct tcphdr) || off > tlen) { goto drop; } tlen -= off; ti->ti_len = tlen; if (off > sizeof(struct tcphdr)) { optlen = off - sizeof(struct tcphdr); optp = mtod(m, char *) + sizeof(struct tcpiphdr); } tiflags = ti->ti_flags; /* * Convert TCP protocol specific fields to host format. */ NTOHL(ti->ti_seq); NTOHL(ti->ti_ack); NTOHS(ti->ti_win); NTOHS(ti->ti_urp); /* * Drop TCP, IP headers and TCP options. */ m->m_data += sizeof(struct tcpiphdr) + off - sizeof(struct tcphdr); m->m_len -= sizeof(struct tcpiphdr) + off - sizeof(struct tcphdr); /* * Locate pcb for segment. */ findso: lhost.ss_family = af; fhost.ss_family = af; switch (af) { case AF_INET: lhost4 = (struct sockaddr_in *)&lhost; lhost4->sin_addr = ti->ti_src; lhost4->sin_port = ti->ti_sport; fhost4 = (struct sockaddr_in *)&fhost; fhost4->sin_addr = ti->ti_dst; fhost4->sin_port = ti->ti_dport; break; case AF_INET6: lhost6 = (struct sockaddr_in6 *)&lhost; lhost6->sin6_addr = ti->ti_src6; lhost6->sin6_port = ti->ti_sport; fhost6 = (struct sockaddr_in6 *)&fhost; fhost6->sin6_addr = ti->ti_dst6; fhost6->sin6_port = ti->ti_dport; break; default: g_assert_not_reached(); } so = solookup(&slirp->tcp_last_so, &slirp->tcb, &lhost, &fhost); /* * If the state is CLOSED (i.e., TCB does not exist) then * all data in the incoming segment is discarded. * If the TCB exists but is in CLOSED state, it is embryonic, * but should either do a listen or a connect soon. * * state == CLOSED means we've done socreate() but haven't * attached it to a protocol yet... * * XXX If a TCB does not exist, and the TH_SYN flag is * the only flag set, then create a session, mark it * as if it was LISTENING, and continue... */ if (so == NULL) { /* TODO: IPv6 */ if (slirp->restricted) { /* Any hostfwds will have an existing socket, so we only get here * for non-hostfwd connections. These should be dropped, unless it * happens to be a guestfwd. */ for (ex_ptr = slirp->guestfwd_list; ex_ptr; ex_ptr = ex_ptr->ex_next) { if (ex_ptr->ex_fport == ti->ti_dport && ti->ti_dst.s_addr == ex_ptr->ex_addr.s_addr) { break; } } if (!ex_ptr) { goto dropwithreset; } } if ((tiflags & (TH_SYN | TH_FIN | TH_RST | TH_URG | TH_ACK)) != TH_SYN) goto dropwithreset; so = socreate(slirp, IPPROTO_TCP); tcp_attach(so); sbreserve(&so->so_snd, TCP_SNDSPACE); sbreserve(&so->so_rcv, TCP_RCVSPACE); so->lhost.ss = lhost; so->fhost.ss = fhost; so->so_iptos = tcp_tos(so); if (so->so_iptos == 0) { switch (af) { case AF_INET: so->so_iptos = ((struct ip *)ti)->ip_tos; break; case AF_INET6: break; default: g_assert_not_reached(); } } tp = sototcpcb(so); tp->t_state = TCPS_LISTEN; } /* * If this is a still-connecting socket, this probably * a retransmit of the SYN. Whether it's a retransmit SYN * or something else, we nuke it. */ if (so->so_state & SS_ISFCONNECTING) goto drop; tp = sototcpcb(so); /* XXX Should never fail */ if (tp == NULL) goto dropwithreset; if (tp->t_state == TCPS_CLOSED) goto drop; tiwin = ti->ti_win; /* * Segment received on connection. * Reset idle time and keep-alive timer. */ tp->t_idle = 0; if (slirp_do_keepalive) tp->t_timer[TCPT_KEEP] = TCPTV_KEEPINTVL; else tp->t_timer[TCPT_KEEP] = TCPTV_KEEP_IDLE; /* * Process options if not in LISTEN state, * else do it below (after getting remote address). */ if (optp && tp->t_state != TCPS_LISTEN) tcp_dooptions(tp, (uint8_t *)optp, optlen, ti); /* * Header prediction: check for the two common cases * of a uni-directional data xfer. If the packet has * no control flags, is in-sequence, the window didn't * change and we're not retransmitting, it's a * candidate. If the length is zero and the ack moved * forward, we're the sender side of the xfer. Just * free the data acked & wake any higher level process * that was blocked waiting for space. If the length * is non-zero and the ack didn't move, we're the * receiver side. If we're getting packets in-order * (the reassembly queue is empty), add the data to * the socket buffer and note that we need a delayed ack. * * XXX Some of these tests are not needed * eg: the tiwin == tp->snd_wnd prevents many more * predictions.. with no *real* advantage.. */ if (tp->t_state == TCPS_ESTABLISHED && (tiflags & (TH_SYN | TH_FIN | TH_RST | TH_URG | TH_ACK)) == TH_ACK && ti->ti_seq == tp->rcv_nxt && tiwin && tiwin == tp->snd_wnd && tp->snd_nxt == tp->snd_max) { if (ti->ti_len == 0) { if (SEQ_GT(ti->ti_ack, tp->snd_una) && SEQ_LEQ(ti->ti_ack, tp->snd_max) && tp->snd_cwnd >= tp->snd_wnd) { /* * this is a pure ack for outstanding data. */ if (tp->t_rtt && SEQ_GT(ti->ti_ack, tp->t_rtseq)) tcp_xmit_timer(tp, tp->t_rtt); acked = ti->ti_ack - tp->snd_una; sodrop(so, acked); tp->snd_una = ti->ti_ack; m_free(m); /* * If all outstanding data are acked, stop * retransmit timer, otherwise restart timer * using current (possibly backed-off) value. * If process is waiting for space, * wakeup/selwakeup/signal. If data * are ready to send, let tcp_output * decide between more output or persist. */ if (tp->snd_una == tp->snd_max) tp->t_timer[TCPT_REXMT] = 0; else if (tp->t_timer[TCPT_PERSIST] == 0) tp->t_timer[TCPT_REXMT] = tp->t_rxtcur; /* * This is called because sowwakeup might have * put data into so_snd. Since we don't so sowwakeup, * we don't need this.. XXX??? */ if (so->so_snd.sb_cc) tcp_output(tp); return; } } else if (ti->ti_ack == tp->snd_una && tcpfrag_list_empty(tp) && ti->ti_len <= sbspace(&so->so_rcv)) { /* * this is a pure, in-sequence data packet * with nothing on the reassembly queue and * we have enough buffer space to take it. */ tp->rcv_nxt += ti->ti_len; /* * Add data to socket buffer. */ if (so->so_emu) { if (tcp_emu(so, m)) sbappend(so, m); } else sbappend(so, m); /* * If this is a short packet, then ACK now - with Nagel * congestion avoidance sender won't send more until * he gets an ACK. * * It is better to not delay acks at all to maximize * TCP throughput. See RFC 2581. */ tp->t_flags |= TF_ACKNOW; tcp_output(tp); return; } } /* header prediction */ /* * Calculate amount of space in receive window, * and then do TCP input processing. * Receive window is amount of space in rcv queue, * but not less than advertised window. */ { int win; win = sbspace(&so->so_rcv); if (win < 0) win = 0; tp->rcv_wnd = MAX(win, (int)(tp->rcv_adv - tp->rcv_nxt)); } switch (tp->t_state) { /* * If the state is LISTEN then ignore segment if it contains an RST. * If the segment contains an ACK then it is bad and send a RST. * If it does not contain a SYN then it is not interesting; drop it. * Don't bother responding if the destination was a broadcast. * Otherwise initialize tp->rcv_nxt, and tp->irs, select an initial * tp->iss, and send a segment: * * Also initialize tp->snd_nxt to tp->iss+1 and tp->snd_una to tp->iss. * Fill in remote peer address fields if not previously specified. * Enter SYN_RECEIVED state, and process any other fields of this * segment in this state. */ case TCPS_LISTEN: { if (tiflags & TH_RST) goto drop; if (tiflags & TH_ACK) goto dropwithreset; if ((tiflags & TH_SYN) == 0) goto drop; /* * This has way too many gotos... * But a bit of spaghetti code never hurt anybody :) */ /* * If this is destined for the control address, then flag to * tcp_ctl once connected, otherwise connect */ /* TODO: IPv6 */ if (af == AF_INET && (so->so_faddr.s_addr & slirp->vnetwork_mask.s_addr) == slirp->vnetwork_addr.s_addr) { if (so->so_faddr.s_addr != slirp->vhost_addr.s_addr && so->so_faddr.s_addr != slirp->vnameserver_addr.s_addr) { /* May be an add exec */ for (ex_ptr = slirp->guestfwd_list; ex_ptr; ex_ptr = ex_ptr->ex_next) { if (ex_ptr->ex_fport == so->so_fport && so->so_faddr.s_addr == ex_ptr->ex_addr.s_addr) { so->so_state |= SS_CTL; break; } } if (so->so_state & SS_CTL) { goto cont_input; } } /* CTL_ALIAS: Do nothing, tcp_fconnect will be called on it */ } if (so->so_emu & EMU_NOCONNECT) { so->so_emu &= ~EMU_NOCONNECT; goto cont_input; } if ((tcp_fconnect(so, so->so_ffamily) == -1) && (errno != EAGAIN) && (errno != EINPROGRESS) && (errno != EWOULDBLOCK)) { uint8_t code; DEBUG_MISC(" tcp fconnect errno = %d-%s", errno, strerror(errno)); if (errno == ECONNREFUSED) { /* ACK the SYN, send RST to refuse the connection */ tcp_respond(tp, ti, m, ti->ti_seq + 1, (tcp_seq)0, TH_RST | TH_ACK, af); } else { switch (af) { case AF_INET: code = ICMP_UNREACH_NET; if (errno == EHOSTUNREACH) { code = ICMP_UNREACH_HOST; } break; case AF_INET6: code = ICMP6_UNREACH_NO_ROUTE; if (errno == EHOSTUNREACH) { code = ICMP6_UNREACH_ADDRESS; } break; default: g_assert_not_reached(); } HTONL(ti->ti_seq); /* restore tcp header */ HTONL(ti->ti_ack); HTONS(ti->ti_win); HTONS(ti->ti_urp); m->m_data -= sizeof(struct tcpiphdr) + off - sizeof(struct tcphdr); m->m_len += sizeof(struct tcpiphdr) + off - sizeof(struct tcphdr); switch (af) { case AF_INET: m->m_data += sizeof(struct tcpiphdr) - sizeof(struct ip) - sizeof(struct tcphdr); m->m_len -= sizeof(struct tcpiphdr) - sizeof(struct ip) - sizeof(struct tcphdr); *ip = save_ip; icmp_send_error(m, ICMP_UNREACH, code, 0, strerror(errno)); break; case AF_INET6: m->m_data += sizeof(struct tcpiphdr) - (sizeof(struct ip6) + sizeof(struct tcphdr)); m->m_len -= sizeof(struct tcpiphdr) - (sizeof(struct ip6) + sizeof(struct tcphdr)); *ip6 = save_ip6; icmp6_send_error(m, ICMP6_UNREACH, code); break; default: g_assert_not_reached(); } } tcp_close(tp); m_free(m); } else { /* * Haven't connected yet, save the current mbuf * and ti, and return * XXX Some OS's don't tell us whether the connect() * succeeded or not. So we must time it out. */ so->so_m = m; so->so_ti = ti; tp->t_timer[TCPT_KEEP] = TCPTV_KEEP_INIT; tp->t_state = TCPS_SYN_RECEIVED; /* * Initialize receive sequence numbers now so that we can send a * valid RST if the remote end rejects our connection. */ tp->irs = ti->ti_seq; tcp_rcvseqinit(tp); tcp_template(tp); } return; cont_conn: /* m==NULL * Check if the connect succeeded */ if (so->so_state & SS_NOFDREF) { tp = tcp_close(tp); goto dropwithreset; } cont_input: tcp_template(tp); if (optp) tcp_dooptions(tp, (uint8_t *)optp, optlen, ti); if (iss) tp->iss = iss; else tp->iss = slirp->tcp_iss; slirp->tcp_iss += TCP_ISSINCR / 2; tp->irs = ti->ti_seq; tcp_sendseqinit(tp); tcp_rcvseqinit(tp); tp->t_flags |= TF_ACKNOW; tp->t_state = TCPS_SYN_RECEIVED; tp->t_timer[TCPT_KEEP] = TCPTV_KEEP_INIT; goto trimthenstep6; } /* case TCPS_LISTEN */ /* * If the state is SYN_SENT: * if seg contains an ACK, but not for our SYN, drop the input. * if seg contains a RST, then drop the connection. * if seg does not contain SYN, then drop it. * Otherwise this is an acceptable SYN segment * initialize tp->rcv_nxt and tp->irs * if seg contains ack then advance tp->snd_una * if SYN has been acked change to ESTABLISHED else SYN_RCVD state * arrange for segment to be acked (eventually) * continue processing rest of data/controls, beginning with URG */ case TCPS_SYN_SENT: if ((tiflags & TH_ACK) && (SEQ_LEQ(ti->ti_ack, tp->iss) || SEQ_GT(ti->ti_ack, tp->snd_max))) goto dropwithreset; if (tiflags & TH_RST) { if (tiflags & TH_ACK) { tcp_drop(tp, 0); /* XXX Check t_softerror! */ } goto drop; } if ((tiflags & TH_SYN) == 0) goto drop; if (tiflags & TH_ACK) { tp->snd_una = ti->ti_ack; if (SEQ_LT(tp->snd_nxt, tp->snd_una)) tp->snd_nxt = tp->snd_una; } tp->t_timer[TCPT_REXMT] = 0; tp->irs = ti->ti_seq; tcp_rcvseqinit(tp); tp->t_flags |= TF_ACKNOW; if (tiflags & TH_ACK && SEQ_GT(tp->snd_una, tp->iss)) { soisfconnected(so); tp->t_state = TCPS_ESTABLISHED; tcp_reass(tp, (struct tcpiphdr *)0, (struct mbuf *)0); /* * if we didn't have to retransmit the SYN, * use its rtt as our initial srtt & rtt var. */ if (tp->t_rtt) tcp_xmit_timer(tp, tp->t_rtt); } else tp->t_state = TCPS_SYN_RECEIVED; trimthenstep6: /* * Advance ti->ti_seq to correspond to first data byte. * If data, trim to stay within window, * dropping FIN if necessary. */ ti->ti_seq++; if (ti->ti_len > tp->rcv_wnd) { todrop = ti->ti_len - tp->rcv_wnd; m_adj(m, -todrop); ti->ti_len = tp->rcv_wnd; tiflags &= ~TH_FIN; } tp->snd_wl1 = ti->ti_seq - 1; tp->rcv_up = ti->ti_seq; goto step6; } /* switch tp->t_state */ /* * States other than LISTEN or SYN_SENT. * Check that at least some bytes of segment are within * receive window. If segment begins before rcv_nxt, * drop leading data (and SYN); if nothing left, just ack. */ todrop = tp->rcv_nxt - ti->ti_seq; if (todrop > 0) { if (tiflags & TH_SYN) { tiflags &= ~TH_SYN; ti->ti_seq++; if (ti->ti_urp > 1) ti->ti_urp--; else tiflags &= ~TH_URG; todrop--; } /* * Following if statement from Stevens, vol. 2, p. 960. */ if (todrop > ti->ti_len || (todrop == ti->ti_len && (tiflags & TH_FIN) == 0)) { /* * Any valid FIN must be to the left of the window. * At this point the FIN must be a duplicate or out * of sequence; drop it. */ tiflags &= ~TH_FIN; /* * Send an ACK to resynchronize and drop any data. * But keep on processing for RST or ACK. */ tp->t_flags |= TF_ACKNOW; todrop = ti->ti_len; } m_adj(m, todrop); ti->ti_seq += todrop; ti->ti_len -= todrop; if (ti->ti_urp > todrop) ti->ti_urp -= todrop; else { tiflags &= ~TH_URG; ti->ti_urp = 0; } } /* * If new data are received on a connection after the * user processes are gone, then RST the other end. */ if ((so->so_state & SS_NOFDREF) && tp->t_state > TCPS_CLOSE_WAIT && ti->ti_len) { tp = tcp_close(tp); goto dropwithreset; } /* * If segment ends after window, drop trailing data * (and PUSH and FIN); if nothing left, just ACK. */ todrop = (ti->ti_seq + ti->ti_len) - (tp->rcv_nxt + tp->rcv_wnd); if (todrop > 0) { if (todrop >= ti->ti_len) { /* * If a new connection request is received * while in TIME_WAIT, drop the old connection * and start over if the sequence numbers * are above the previous ones. */ if (tiflags & TH_SYN && tp->t_state == TCPS_TIME_WAIT && SEQ_GT(ti->ti_seq, tp->rcv_nxt)) { iss = tp->rcv_nxt + TCP_ISSINCR; tp = tcp_close(tp); goto findso; } /* * If window is closed can only take segments at * window edge, and have to drop data and PUSH from * incoming segments. Continue processing, but * remember to ack. Otherwise, drop segment * and ack. */ if (tp->rcv_wnd == 0 && ti->ti_seq == tp->rcv_nxt) { tp->t_flags |= TF_ACKNOW; } else { goto dropafterack; } } m_adj(m, -todrop); ti->ti_len -= todrop; tiflags &= ~(TH_PUSH | TH_FIN); } /* * If the RST bit is set examine the state: * SYN_RECEIVED STATE: * If passive open, return to LISTEN state. * If active open, inform user that connection was refused. * ESTABLISHED, FIN_WAIT_1, FIN_WAIT2, CLOSE_WAIT STATES: * Inform user that connection was reset, and close tcb. * CLOSING, LAST_ACK, TIME_WAIT STATES * Close the tcb. */ if (tiflags & TH_RST) switch (tp->t_state) { case TCPS_SYN_RECEIVED: case TCPS_ESTABLISHED: case TCPS_FIN_WAIT_1: case TCPS_FIN_WAIT_2: case TCPS_CLOSE_WAIT: tp->t_state = TCPS_CLOSED; tcp_close(tp); goto drop; case TCPS_CLOSING: case TCPS_LAST_ACK: case TCPS_TIME_WAIT: tcp_close(tp); goto drop; } /* * If a SYN is in the window, then this is an * error and we send an RST and drop the connection. */ if (tiflags & TH_SYN) { tp = tcp_drop(tp, 0); goto dropwithreset; } /* * If the ACK bit is off we drop the segment and return. */ if ((tiflags & TH_ACK) == 0) goto drop; /* * Ack processing. */ switch (tp->t_state) { /* * In SYN_RECEIVED state if the ack ACKs our SYN then enter * ESTABLISHED state and continue processing, otherwise * send an RST. una<=ack<=max */ case TCPS_SYN_RECEIVED: if (SEQ_GT(tp->snd_una, ti->ti_ack) || SEQ_GT(ti->ti_ack, tp->snd_max)) goto dropwithreset; tp->t_state = TCPS_ESTABLISHED; /* * The sent SYN is ack'ed with our sequence number +1 * The first data byte already in the buffer will get * lost if no correction is made. This is only needed for * SS_CTL since the buffer is empty otherwise. * tp->snd_una++; or: */ tp->snd_una = ti->ti_ack; if (so->so_state & SS_CTL) { /* So tcp_ctl reports the right state */ ret = tcp_ctl(so); if (ret == 1) { soisfconnected(so); so->so_state &= ~SS_CTL; /* success XXX */ } else if (ret == 2) { so->so_state &= SS_PERSISTENT_MASK; so->so_state |= SS_NOFDREF; /* CTL_CMD */ } else { needoutput = 1; tp->t_state = TCPS_FIN_WAIT_1; } } else { soisfconnected(so); } tcp_reass(tp, (struct tcpiphdr *)0, (struct mbuf *)0); tp->snd_wl1 = ti->ti_seq - 1; /* Avoid ack processing; snd_una==ti_ack => dup ack */ goto synrx_to_est; /* fall into ... */ /* * In ESTABLISHED state: drop duplicate ACKs; ACK out of range * ACKs. If the ack is in the range * tp->snd_una < ti->ti_ack <= tp->snd_max * then advance tp->snd_una to ti->ti_ack and drop * data from the retransmission queue. If this ACK reflects * more up to date window information we update our window information. */ case TCPS_ESTABLISHED: case TCPS_FIN_WAIT_1: case TCPS_FIN_WAIT_2: case TCPS_CLOSE_WAIT: case TCPS_CLOSING: case TCPS_LAST_ACK: case TCPS_TIME_WAIT: if (SEQ_LEQ(ti->ti_ack, tp->snd_una)) { if (ti->ti_len == 0 && tiwin == tp->snd_wnd) { DEBUG_MISC(" dup ack m = %p so = %p", m, so); /* * If we have outstanding data (other than * a window probe), this is a completely * duplicate ack (ie, window info didn't * change), the ack is the biggest we've * seen and we've seen exactly our rexmt * threshold of them, assume a packet * has been dropped and retransmit it. * Kludge snd_nxt & the congestion * window so we send only this one * packet. * * We know we're losing at the current * window size so do congestion avoidance * (set ssthresh to half the current window * and pull our congestion window back to * the new ssthresh). * * Dup acks mean that packets have left the * network (they're now cached at the receiver) * so bump cwnd by the amount in the receiver * to keep a constant cwnd packets in the * network. */ if (tp->t_timer[TCPT_REXMT] == 0 || ti->ti_ack != tp->snd_una) tp->t_dupacks = 0; else if (++tp->t_dupacks == TCPREXMTTHRESH) { tcp_seq onxt = tp->snd_nxt; unsigned win = MIN(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_maxseg; if (win < 2) win = 2; tp->snd_ssthresh = win * tp->t_maxseg; tp->t_timer[TCPT_REXMT] = 0; tp->t_rtt = 0; tp->snd_nxt = ti->ti_ack; tp->snd_cwnd = tp->t_maxseg; tcp_output(tp); tp->snd_cwnd = tp->snd_ssthresh + tp->t_maxseg * tp->t_dupacks; if (SEQ_GT(onxt, tp->snd_nxt)) tp->snd_nxt = onxt; goto drop; } else if (tp->t_dupacks > TCPREXMTTHRESH) { tp->snd_cwnd += tp->t_maxseg; tcp_output(tp); goto drop; } } else tp->t_dupacks = 0; break; } synrx_to_est: /* * If the congestion window was inflated to account * for the other side's cached packets, retract it. */ if (tp->t_dupacks > TCPREXMTTHRESH && tp->snd_cwnd > tp->snd_ssthresh) tp->snd_cwnd = tp->snd_ssthresh; tp->t_dupacks = 0; if (SEQ_GT(ti->ti_ack, tp->snd_max)) { goto dropafterack; } acked = ti->ti_ack - tp->snd_una; /* * If transmit timer is running and timed sequence * number was acked, update smoothed round trip time. * Since we now have an rtt measurement, cancel the * timer backoff (cf., Phil Karn's retransmit alg.). * Recompute the initial retransmit timer. */ if (tp->t_rtt && SEQ_GT(ti->ti_ack, tp->t_rtseq)) tcp_xmit_timer(tp, tp->t_rtt); /* * If all outstanding data is acked, stop retransmit * timer and remember to restart (more output or persist). * If there is more data to be acked, restart retransmit * timer, using current (possibly backed-off) value. */ if (ti->ti_ack == tp->snd_max) { tp->t_timer[TCPT_REXMT] = 0; needoutput = 1; } else if (tp->t_timer[TCPT_PERSIST] == 0) tp->t_timer[TCPT_REXMT] = tp->t_rxtcur; /* * When new data is acked, open the congestion window. * If the window gives us less than ssthresh packets * in flight, open exponentially (maxseg per packet). * Otherwise open linearly: maxseg per window * (maxseg^2 / cwnd per packet). */ { register unsigned cw = tp->snd_cwnd; register unsigned incr = tp->t_maxseg; if (cw > tp->snd_ssthresh) incr = incr * incr / cw; tp->snd_cwnd = MIN(cw + incr, TCP_MAXWIN << tp->snd_scale); } if (acked > so->so_snd.sb_cc) { tp->snd_wnd -= so->so_snd.sb_cc; sodrop(so, (int)so->so_snd.sb_cc); ourfinisacked = 1; } else { sodrop(so, acked); tp->snd_wnd -= acked; ourfinisacked = 0; } tp->snd_una = ti->ti_ack; if (SEQ_LT(tp->snd_nxt, tp->snd_una)) tp->snd_nxt = tp->snd_una; switch (tp->t_state) { /* * In FIN_WAIT_1 STATE in addition to the processing * for the ESTABLISHED state if our FIN is now acknowledged * then enter FIN_WAIT_2. */ case TCPS_FIN_WAIT_1: if (ourfinisacked) { /* * If we can't receive any more * data, then closing user can proceed. * Starting the timer is contrary to the * specification, but if we don't get a FIN * we'll hang forever. */ if (so->so_state & SS_FCANTRCVMORE) { tp->t_timer[TCPT_2MSL] = TCP_MAXIDLE; } tp->t_state = TCPS_FIN_WAIT_2; } break; /* * In CLOSING STATE in addition to the processing for * the ESTABLISHED state if the ACK acknowledges our FIN * then enter the TIME-WAIT state, otherwise ignore * the segment. */ case TCPS_CLOSING: if (ourfinisacked) { tp->t_state = TCPS_TIME_WAIT; tcp_canceltimers(tp); tp->t_timer[TCPT_2MSL] = 2 * TCPTV_MSL; } break; /* * In LAST_ACK, we may still be waiting for data to drain * and/or to be acked, as well as for the ack of our FIN. * If our FIN is now acknowledged, delete the TCB, * enter the closed state and return. */ case TCPS_LAST_ACK: if (ourfinisacked) { tcp_close(tp); goto drop; } break; /* * In TIME_WAIT state the only thing that should arrive * is a retransmission of the remote FIN. Acknowledge * it and restart the finack timer. */ case TCPS_TIME_WAIT: tp->t_timer[TCPT_2MSL] = 2 * TCPTV_MSL; goto dropafterack; } } /* switch(tp->t_state) */ step6: /* * Update window information. * Don't look at window if no ACK: TAC's send garbage on first SYN. */ if ((tiflags & TH_ACK) && (SEQ_LT(tp->snd_wl1, ti->ti_seq) || (tp->snd_wl1 == ti->ti_seq && (SEQ_LT(tp->snd_wl2, ti->ti_ack) || (tp->snd_wl2 == ti->ti_ack && tiwin > tp->snd_wnd))))) { tp->snd_wnd = tiwin; tp->snd_wl1 = ti->ti_seq; tp->snd_wl2 = ti->ti_ack; if (tp->snd_wnd > tp->max_sndwnd) tp->max_sndwnd = tp->snd_wnd; needoutput = 1; } /* * Process segments with URG. */ if ((tiflags & TH_URG) && ti->ti_urp && TCPS_HAVERCVDFIN(tp->t_state) == 0) { /* * This is a kludge, but if we receive and accept * random urgent pointers, we'll crash in * soreceive. It's hard to imagine someone * actually wanting to send this much urgent data. */ if (ti->ti_urp + so->so_rcv.sb_cc > so->so_rcv.sb_datalen) { ti->ti_urp = 0; tiflags &= ~TH_URG; goto dodata; } /* * If this segment advances the known urgent pointer, * then mark the data stream. This should not happen * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since * a FIN has been received from the remote side. * In these states we ignore the URG. * * According to RFC961 (Assigned Protocols), * the urgent pointer points to the last octet * of urgent data. We continue, however, * to consider it to indicate the first octet * of data past the urgent section as the original * spec states (in one of two places). */ if (SEQ_GT(ti->ti_seq + ti->ti_urp, tp->rcv_up)) { tp->rcv_up = ti->ti_seq + ti->ti_urp; so->so_urgc = so->so_rcv.sb_cc + (tp->rcv_up - tp->rcv_nxt); /* -1; */ tp->rcv_up = ti->ti_seq + ti->ti_urp; } } else /* * If no out of band data is expected, * pull receive urgent pointer along * with the receive window. */ if (SEQ_GT(tp->rcv_nxt, tp->rcv_up)) tp->rcv_up = tp->rcv_nxt; dodata: /* * If this is a small packet, then ACK now - with Nagel * congestion avoidance sender won't send more until * he gets an ACK. */ if (ti->ti_len && (unsigned)ti->ti_len <= 5 && ((struct tcpiphdr_2 *)ti)->first_char == (char)27) { tp->t_flags |= TF_ACKNOW; } /* * Process the segment text, merging it into the TCP sequencing queue, * and arranging for acknowledgment of receipt if necessary. * This process logically involves adjusting tp->rcv_wnd as data * is presented to the user (this happens in tcp_usrreq.c, * case PRU_RCVD). If a FIN has already been received on this * connection then we just ignore the text. */ if ((ti->ti_len || (tiflags & TH_FIN)) && TCPS_HAVERCVDFIN(tp->t_state) == 0) { TCP_REASS(tp, ti, m, so, tiflags); } else { m_free(m); tiflags &= ~TH_FIN; } /* * If FIN is received ACK the FIN and let the user know * that the connection is closing. */ if (tiflags & TH_FIN) { if (TCPS_HAVERCVDFIN(tp->t_state) == 0) { /* * If we receive a FIN we can't send more data, * set it SS_FDRAIN * Shutdown the socket if there is no rx data in the * buffer. * soread() is called on completion of shutdown() and * will got to TCPS_LAST_ACK, and use tcp_output() * to send the FIN. */ sofwdrain(so); tp->t_flags |= TF_ACKNOW; tp->rcv_nxt++; } switch (tp->t_state) { /* * In SYN_RECEIVED and ESTABLISHED STATES * enter the CLOSE_WAIT state. */ case TCPS_SYN_RECEIVED: case TCPS_ESTABLISHED: if (so->so_emu == EMU_CTL) /* no shutdown on socket */ tp->t_state = TCPS_LAST_ACK; else tp->t_state = TCPS_CLOSE_WAIT; break; /* * If still in FIN_WAIT_1 STATE FIN has not been acked so * enter the CLOSING state. */ case TCPS_FIN_WAIT_1: tp->t_state = TCPS_CLOSING; break; /* * In FIN_WAIT_2 state enter the TIME_WAIT state, * starting the time-wait timer, turning off the other * standard timers. */ case TCPS_FIN_WAIT_2: tp->t_state = TCPS_TIME_WAIT; tcp_canceltimers(tp); tp->t_timer[TCPT_2MSL] = 2 * TCPTV_MSL; break; /* * In TIME_WAIT state restart the 2 MSL time_wait timer. */ case TCPS_TIME_WAIT: tp->t_timer[TCPT_2MSL] = 2 * TCPTV_MSL; break; } } /* * Return any desired output. */ if (needoutput || (tp->t_flags & TF_ACKNOW)) { tcp_output(tp); } return; dropafterack: /* * Generate an ACK dropping incoming segment if it occupies * sequence space, where the ACK reflects our state. */ if (tiflags & TH_RST) goto drop; m_free(m); tp->t_flags |= TF_ACKNOW; tcp_output(tp); return; dropwithreset: /* reuses m if m!=NULL, m_free() unnecessary */ if (tiflags & TH_ACK) tcp_respond(tp, ti, m, (tcp_seq)0, ti->ti_ack, TH_RST, af); else { if (tiflags & TH_SYN) ti->ti_len++; tcp_respond(tp, ti, m, ti->ti_seq + ti->ti_len, (tcp_seq)0, TH_RST | TH_ACK, af); } return; drop: /* * Drop space held by incoming segment and return. */ m_free(m); } static void tcp_dooptions(struct tcpcb *tp, uint8_t *cp, int cnt, struct tcpiphdr *ti) { uint16_t mss; int opt, optlen; DEBUG_CALL("tcp_dooptions"); DEBUG_ARG("tp = %p cnt=%i", tp, cnt); for (; cnt > 0; cnt -= optlen, cp += optlen) { opt = cp[0]; if (opt == TCPOPT_EOL) break; if (opt == TCPOPT_NOP) optlen = 1; else { optlen = cp[1]; if (optlen <= 0) break; } switch (opt) { default: continue; case TCPOPT_MAXSEG: if (optlen != TCPOLEN_MAXSEG) continue; if (!(ti->ti_flags & TH_SYN)) continue; memcpy((char *)&mss, (char *)cp + 2, sizeof(mss)); NTOHS(mss); tcp_mss(tp, mss); /* sets t_maxseg */ break; } } } /* * Collect new round-trip time estimate * and update averages and current timeout. */ static void tcp_xmit_timer(register struct tcpcb *tp, int rtt) { register short delta; DEBUG_CALL("tcp_xmit_timer"); DEBUG_ARG("tp = %p", tp); DEBUG_ARG("rtt = %d", rtt); if (tp->t_srtt != 0) { /* * srtt is stored as fixed point with 3 bits after the * binary point (i.e., scaled by 8). The following magic * is equivalent to the smoothing algorithm in rfc793 with * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed * point). Adjust rtt to origin 0. */ delta = rtt - 1 - (tp->t_srtt >> TCP_RTT_SHIFT); if ((tp->t_srtt += delta) <= 0) tp->t_srtt = 1; /* * We accumulate a smoothed rtt variance (actually, a * smoothed mean difference), then set the retransmit * timer to smoothed rtt + 4 times the smoothed variance. * rttvar is stored as fixed point with 2 bits after the * binary point (scaled by 4). The following is * equivalent to rfc793 smoothing with an alpha of .75 * (rttvar = rttvar*3/4 + |delta| / 4). This replaces * rfc793's wired-in beta. */ if (delta < 0) delta = -delta; delta -= (tp->t_rttvar >> TCP_RTTVAR_SHIFT); if ((tp->t_rttvar += delta) <= 0) tp->t_rttvar = 1; } else { /* * No rtt measurement yet - use the unsmoothed rtt. * Set the variance to half the rtt (so our first * retransmit happens at 3*rtt). */ tp->t_srtt = rtt << TCP_RTT_SHIFT; tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1); } tp->t_rtt = 0; tp->t_rxtshift = 0; /* * the retransmit should happen at rtt + 4 * rttvar. * Because of the way we do the smoothing, srtt and rttvar * will each average +1/2 tick of bias. When we compute * the retransmit timer, we want 1/2 tick of rounding and * 1 extra tick because of +-1/2 tick uncertainty in the * firing of the timer. The bias will give us exactly the * 1.5 tick we need. But, because the bias is * statistical, we have to test that we don't drop below * the minimum feasible timer (which is 2 ticks). */ TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp), (short)tp->t_rttmin, TCPTV_REXMTMAX); /* XXX */ /* * We received an ack for a packet that wasn't retransmitted; * it is probably safe to discard any error indications we've * received recently. This isn't quite right, but close enough * for now (a route might have failed after we sent a segment, * and the return path might not be symmetrical). */ tp->t_softerror = 0; } /* * Determine a reasonable value for maxseg size. * If the route is known, check route for mtu. * If none, use an mss that can be handled on the outgoing * interface without forcing IP to fragment; if bigger than * an mbuf cluster (MCLBYTES), round down to nearest multiple of MCLBYTES * to utilize large mbufs. If no route is found, route has no mtu, * or the destination isn't local, use a default, hopefully conservative * size (usually 512 or the default IP max size, but no more than the mtu * of the interface), as we can't discover anything about intervening * gateways or networks. We also initialize the congestion/slow start * window to be a single segment if the destination isn't local. * While looking at the routing entry, we also initialize other path-dependent * parameters from pre-set or cached values in the routing entry. */ int tcp_mss(struct tcpcb *tp, unsigned offer) { struct socket *so = tp->t_socket; int mss; DEBUG_CALL("tcp_mss"); DEBUG_ARG("tp = %p", tp); DEBUG_ARG("offer = %d", offer); switch (so->so_ffamily) { case AF_INET: mss = MIN(so->slirp->if_mtu, so->slirp->if_mru) - sizeof(struct tcphdr) - sizeof(struct ip); break; case AF_INET6: mss = MIN(so->slirp->if_mtu, so->slirp->if_mru) - sizeof(struct tcphdr) - sizeof(struct ip6); break; default: g_assert_not_reached(); } if (offer) mss = MIN(mss, offer); mss = MAX(mss, 32); if (mss < tp->t_maxseg || offer != 0) tp->t_maxseg = MIN(mss, TCP_MAXSEG_MAX); tp->snd_cwnd = mss; sbreserve(&so->so_snd, TCP_SNDSPACE + ((TCP_SNDSPACE % mss) ? (mss - (TCP_SNDSPACE % mss)) : 0)); sbreserve(&so->so_rcv, TCP_RCVSPACE + ((TCP_RCVSPACE % mss) ? (mss - (TCP_RCVSPACE % mss)) : 0)); DEBUG_MISC(" returning mss = %d", mss); return mss; }