/* * INET An implementation of the TCP/IP protocol suite for the LINUX * operating system. INET is implemented using the BSD Socket * interface as the means of communication with the user level. * * Implementation of the Transmission Control Protocol(TCP). * * Version: $Id: tcp_input.c,v 1.243 2002/02/01 22:01:04 davem Exp $ * * Authors: Ross Biro, <bir7@leland.Stanford.Edu> * Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG> * Mark Evans, <evansmp@uhura.aston.ac.uk> * Corey Minyard <wf-rch!minyard@relay.EU.net> * Florian La Roche, <flla@stud.uni-sb.de> * Charles Hedrick, <hedrick@klinzhai.rutgers.edu> * Linus Torvalds, <torvalds@cs.helsinki.fi> * Alan Cox, <gw4pts@gw4pts.ampr.org> * Matthew Dillon, <dillon@apollo.west.oic.com> * Arnt Gulbrandsen, <agulbra@nvg.unit.no> * Jorge Cwik, <jorge@laser.satlink.net> */ /* * Changes: * Pedro Roque : Fast Retransmit/Recovery. * Two receive queues. * Retransmit queue handled by TCP. * Better retransmit timer handling. * New congestion avoidance. * Header prediction. * Variable renaming. * * Eric : Fast Retransmit. * Randy Scott : MSS option defines. * Eric Schenk : Fixes to slow start algorithm. * Eric Schenk : Yet another double ACK bug. * Eric Schenk : Delayed ACK bug fixes. * Eric Schenk : Floyd style fast retrans war avoidance. * David S. Miller : Don't allow zero congestion window. * Eric Schenk : Fix retransmitter so that it sends * next packet on ack of previous packet. * Andi Kleen : Moved open_request checking here * and process RSTs for open_requests. * Andi Kleen : Better prune_queue, and other fixes. * Andrey Savochkin: Fix RTT measurements in the presnce of * timestamps. * Andrey Savochkin: Check sequence numbers correctly when * removing SACKs due to in sequence incoming * data segments. * Andi Kleen: Make sure we never ack data there is not * enough room for. Also make this condition * a fatal error if it might still happen. * Andi Kleen: Add tcp_measure_rcv_mss to make * connections with MSS<min(MTU,ann. MSS) * work without delayed acks. * Andi Kleen: Process packets with PSH set in the * fast path. * J Hadi Salim: ECN support * Andrei Gurtov, * Pasi Sarolahti, * Panu Kuhlberg: Experimental audit of TCP (re)transmission * engine. Lots of bugs are found. * Pasi Sarolahti: F-RTO for dealing with spurious RTOs */ #include <linux/config.h> #include <linux/mm.h> #include <linux/sysctl.h> #include <net/tcp.h> #include <net/inet_common.h> #include <linux/ipsec.h> int sysctl_tcp_timestamps = 1; int sysctl_tcp_window_scaling = 1; int sysctl_tcp_sack = 1; int sysctl_tcp_fack = 1; int sysctl_tcp_reordering = TCP_FASTRETRANS_THRESH; #ifdef CONFIG_INET_ECN int sysctl_tcp_ecn = 1; #else int sysctl_tcp_ecn; #endif int sysctl_tcp_dsack = 1; int sysctl_tcp_app_win = 31; int sysctl_tcp_adv_win_scale = 2; int sysctl_tcp_stdurg; int sysctl_tcp_rfc1337; int sysctl_tcp_max_orphans = NR_FILE; int sysctl_tcp_frto; #define FLAG_DATA 0x01 /* Incoming frame contained data. */ #define FLAG_WIN_UPDATE 0x02 /* Incoming ACK was a window update. */ #define FLAG_DATA_ACKED 0x04 /* This ACK acknowledged new data. */ #define FLAG_RETRANS_DATA_ACKED 0x08 /* "" "" some of which was retransmitted. */ #define FLAG_SYN_ACKED 0x10 /* This ACK acknowledged SYN. */ #define FLAG_DATA_SACKED 0x20 /* New SACK. */ #define FLAG_ECE 0x40 /* ECE in this ACK */ #define FLAG_DATA_LOST 0x80 /* SACK detected data lossage. */ #define FLAG_SLOWPATH 0x100 /* Do not skip RFC checks for window update.*/ #define FLAG_ACKED (FLAG_DATA_ACKED|FLAG_SYN_ACKED) #define FLAG_NOT_DUP (FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED) #define FLAG_CA_ALERT (FLAG_DATA_SACKED|FLAG_ECE) #define FLAG_FORWARD_PROGRESS (FLAG_ACKED|FLAG_DATA_SACKED) #define IsReno(tp) ((tp)->sack_ok == 0) #define IsFack(tp) ((tp)->sack_ok & 2) #define IsDSack(tp) ((tp)->sack_ok & 4) #define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH) /* Adapt the MSS value used to make delayed ack decision to the * real world. */ static __inline__ void tcp_measure_rcv_mss(struct tcp_opt *tp, struct sk_buff *skb) { unsigned int len, lss; lss = tp->ack.last_seg_size; tp->ack.last_seg_size = 0; /* skb->len may jitter because of SACKs, even if peer * sends good full-sized frames. */ len = skb->len; if (len >= tp->ack.rcv_mss) { tp->ack.rcv_mss = len; } else { /* Otherwise, we make more careful check taking into account, * that SACKs block is variable. * * "len" is invariant segment length, including TCP header. */ len += skb->data - skb->h.raw; if (len >= TCP_MIN_RCVMSS + sizeof(struct tcphdr) || /* If PSH is not set, packet should be * full sized, provided peer TCP is not badly broken. * This observation (if it is correct 8)) allows * to handle super-low mtu links fairly. */ (len >= TCP_MIN_MSS + sizeof(struct tcphdr) && !(tcp_flag_word(skb->h.th)&TCP_REMNANT))) { /* Subtract also invariant (if peer is RFC compliant), * tcp header plus fixed timestamp option length. * Resulting "len" is MSS free of SACK jitter. */ len -= tp->tcp_header_len; tp->ack.last_seg_size = len; if (len == lss) { tp->ack.rcv_mss = len; return; } } tp->ack.pending |= TCP_ACK_PUSHED; } } static void tcp_incr_quickack(struct tcp_opt *tp) { unsigned quickacks = tp->rcv_wnd/(2*tp->ack.rcv_mss); if (quickacks==0) quickacks=2; if (quickacks > tp->ack.quick) tp->ack.quick = min(quickacks, TCP_MAX_QUICKACKS); } void tcp_enter_quickack_mode(struct tcp_opt *tp) { tcp_incr_quickack(tp); tp->ack.pingpong = 0; tp->ack.ato = TCP_ATO_MIN; } /* Send ACKs quickly, if "quick" count is not exhausted * and the session is not interactive. */ static __inline__ int tcp_in_quickack_mode(struct tcp_opt *tp) { return (tp->ack.quick && !tp->ack.pingpong); } /* Buffer size and advertised window tuning. * * 1. Tuning sk->sk_sndbuf, when connection enters established state. */ static void tcp_fixup_sndbuf(struct sock *sk) { int sndmem = tcp_sk(sk)->mss_clamp + MAX_TCP_HEADER + 16 + sizeof(struct sk_buff); if (sk->sk_sndbuf < 3 * sndmem) sk->sk_sndbuf = min(3 * sndmem, sysctl_tcp_wmem[2]); } /* 2. Tuning advertised window (window_clamp, rcv_ssthresh) * * All tcp_full_space() is split to two parts: "network" buffer, allocated * forward and advertised in receiver window (tp->rcv_wnd) and * "application buffer", required to isolate scheduling/application * latencies from network. * window_clamp is maximal advertised window. It can be less than * tcp_full_space(), in this case tcp_full_space() - window_clamp * is reserved for "application" buffer. The less window_clamp is * the smoother our behaviour from viewpoint of network, but the lower * throughput and the higher sensitivity of the connection to losses. 8) * * rcv_ssthresh is more strict window_clamp used at "slow start" * phase to predict further behaviour of this connection. * It is used for two goals: * - to enforce header prediction at sender, even when application * requires some significant "application buffer". It is check #1. * - to prevent pruning of receive queue because of misprediction * of receiver window. Check #2. * * The scheme does not work when sender sends good segments opening * window and then starts to feed us spagetti. But it should work * in common situations. Otherwise, we have to rely on queue collapsing. */ /* Slow part of check#2. */ static int __tcp_grow_window(struct sock *sk, struct tcp_opt *tp, struct sk_buff *skb) { /* Optimize this! */ int truesize = tcp_win_from_space(skb->truesize)/2; int window = tcp_full_space(sk)/2; while (tp->rcv_ssthresh <= window) { if (truesize <= skb->len) return 2*tp->ack.rcv_mss; truesize >>= 1; window >>= 1; } return 0; } static __inline__ void tcp_grow_window(struct sock *sk, struct tcp_opt *tp, struct sk_buff *skb) { /* Check #1 */ if (tp->rcv_ssthresh < tp->window_clamp && (int)tp->rcv_ssthresh < tcp_space(sk) && !tcp_memory_pressure) { int incr; /* Check #2. Increase window, if skb with such overhead * will fit to rcvbuf in future. */ if (tcp_win_from_space(skb->truesize) <= skb->len) incr = 2*tp->advmss; else incr = __tcp_grow_window(sk, tp, skb); if (incr) { tp->rcv_ssthresh = min(tp->rcv_ssthresh + incr, tp->window_clamp); tp->ack.quick |= 1; } } } /* 3. Tuning rcvbuf, when connection enters established state. */ static void tcp_fixup_rcvbuf(struct sock *sk) { struct tcp_opt *tp = tcp_sk(sk); int rcvmem = tp->advmss + MAX_TCP_HEADER + 16 + sizeof(struct sk_buff); /* Try to select rcvbuf so that 4 mss-sized segments * will fit to window and correspoding skbs will fit to our rcvbuf. * (was 3; 4 is minimum to allow fast retransmit to work.) */ while (tcp_win_from_space(rcvmem) < tp->advmss) rcvmem += 128; if (sk->sk_rcvbuf < 4 * rcvmem) sk->sk_rcvbuf = min(4 * rcvmem, sysctl_tcp_rmem[2]); } /* 4. Try to fixup all. It is made iimediately after connection enters * established state. */ static void tcp_init_buffer_space(struct sock *sk) { struct tcp_opt *tp = tcp_sk(sk); int maxwin; if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) tcp_fixup_rcvbuf(sk); if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK)) tcp_fixup_sndbuf(sk); maxwin = tcp_full_space(sk); if (tp->window_clamp >= maxwin) { tp->window_clamp = maxwin; if (sysctl_tcp_app_win && maxwin > 4 * tp->advmss) tp->window_clamp = max(maxwin - (maxwin >> sysctl_tcp_app_win), 4 * tp->advmss); } /* Force reservation of one segment. */ if (sysctl_tcp_app_win && tp->window_clamp > 2 * tp->advmss && tp->window_clamp + tp->advmss > maxwin) tp->window_clamp = max(2 * tp->advmss, maxwin - tp->advmss); tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp); tp->snd_cwnd_stamp = tcp_time_stamp; } /* 5. Recalculate window clamp after socket hit its memory bounds. */ static void tcp_clamp_window(struct sock *sk, struct tcp_opt *tp) { struct sk_buff *skb; unsigned int app_win = tp->rcv_nxt - tp->copied_seq; int ofo_win = 0; tp->ack.quick = 0; skb_queue_walk(&tp->out_of_order_queue, skb) { ofo_win += skb->len; } /* If overcommit is due to out of order segments, * do not clamp window. Try to expand rcvbuf instead. */ if (ofo_win) { if (sk->sk_rcvbuf < sysctl_tcp_rmem[2] && !(sk->sk_userlocks & SOCK_RCVBUF_LOCK) && !tcp_memory_pressure && atomic_read(&tcp_memory_allocated) < sysctl_tcp_mem[0]) sk->sk_rcvbuf = min(atomic_read(&sk->sk_rmem_alloc), sysctl_tcp_rmem[2]); } if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf) { app_win += ofo_win; if (atomic_read(&sk->sk_rmem_alloc) >= 2 * sk->sk_rcvbuf) app_win >>= 1; if (app_win > tp->ack.rcv_mss) app_win -= tp->ack.rcv_mss; app_win = max(app_win, 2U*tp->advmss); if (!ofo_win) tp->window_clamp = min(tp->window_clamp, app_win); tp->rcv_ssthresh = min(tp->window_clamp, 2U*tp->advmss); } } /* There is something which you must keep in mind when you analyze the * behavior of the tp->ato delayed ack timeout interval. When a * connection starts up, we want to ack as quickly as possible. The * problem is that "good" TCP's do slow start at the beginning of data * transmission. The means that until we send the first few ACK's the * sender will sit on his end and only queue most of his data, because * he can only send snd_cwnd unacked packets at any given time. For * each ACK we send, he increments snd_cwnd and transmits more of his * queue. -DaveM */ static void tcp_event_data_recv(struct sock *sk, struct tcp_opt *tp, struct sk_buff *skb) { u32 now; tcp_schedule_ack(tp); tcp_measure_rcv_mss(tp, skb); now = tcp_time_stamp; if (!tp->ack.ato) { /* The _first_ data packet received, initialize * delayed ACK engine. */ tcp_incr_quickack(tp); tp->ack.ato = TCP_ATO_MIN; } else { int m = now - tp->ack.lrcvtime; if (m <= TCP_ATO_MIN/2) { /* The fastest case is the first. */ tp->ack.ato = (tp->ack.ato>>1) + TCP_ATO_MIN/2; } else if (m < tp->ack.ato) { tp->ack.ato = (tp->ack.ato>>1) + m; if (tp->ack.ato > tp->rto) tp->ack.ato = tp->rto; } else if (m > tp->rto) { /* Too long gap. Apparently sender falled to * restart window, so that we send ACKs quickly. */ tcp_incr_quickack(tp); tcp_mem_reclaim(sk); } } tp->ack.lrcvtime = now; TCP_ECN_check_ce(tp, skb); if (skb->len >= 128) tcp_grow_window(sk, tp, skb); } /* Called to compute a smoothed rtt estimate. The data fed to this * routine either comes from timestamps, or from segments that were * known _not_ to have been retransmitted [see Karn/Partridge * Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88 * piece by Van Jacobson. * NOTE: the next three routines used to be one big routine. * To save cycles in the RFC 1323 implementation it was better to break * it up into three procedures. -- erics */ static void tcp_rtt_estimator(struct tcp_opt *tp, __u32 mrtt) { long m = mrtt; /* RTT */ /* The following amusing code comes from Jacobson's * article in SIGCOMM '88. Note that rtt and mdev * are scaled versions of rtt and mean deviation. * This is designed to be as fast as possible * m stands for "measurement". * * On a 1990 paper the rto value is changed to: * RTO = rtt + 4 * mdev * * Funny. This algorithm seems to be very broken. * These formulae increase RTO, when it should be decreased, increase * too slowly, when it should be incresed fastly, decrease too fastly * etc. I guess in BSD RTO takes ONE value, so that it is absolutely * does not matter how to _calculate_ it. Seems, it was trap * that VJ failed to avoid. 8) */ if(m == 0) m = 1; if (tp->srtt != 0) { m -= (tp->srtt >> 3); /* m is now error in rtt est */ tp->srtt += m; /* rtt = 7/8 rtt + 1/8 new */ if (m < 0) { m = -m; /* m is now abs(error) */ m -= (tp->mdev >> 2); /* similar update on mdev */ /* This is similar to one of Eifel findings. * Eifel blocks mdev updates when rtt decreases. * This solution is a bit different: we use finer gain * for mdev in this case (alpha*beta). * Like Eifel it also prevents growth of rto, * but also it limits too fast rto decreases, * happening in pure Eifel. */ if (m > 0) m >>= 3; } else { m -= (tp->mdev >> 2); /* similar update on mdev */ } tp->mdev += m; /* mdev = 3/4 mdev + 1/4 new */ if (tp->mdev > tp->mdev_max) { tp->mdev_max = tp->mdev; if (tp->mdev_max > tp->rttvar) tp->rttvar = tp->mdev_max; } if (after(tp->snd_una, tp->rtt_seq)) { if (tp->mdev_max < tp->rttvar) tp->rttvar -= (tp->rttvar-tp->mdev_max)>>2; tp->rtt_seq = tp->snd_nxt; tp->mdev_max = TCP_RTO_MIN; } } else { /* no previous measure. */ tp->srtt = m<<3; /* take the measured time to be rtt */ tp->mdev = m<<1; /* make sure rto = 3*rtt */ tp->mdev_max = tp->rttvar = max(tp->mdev, TCP_RTO_MIN); tp->rtt_seq = tp->snd_nxt; } } /* Calculate rto without backoff. This is the second half of Van Jacobson's * routine referred to above. */ static __inline__ void tcp_set_rto(struct tcp_opt *tp) { /* Old crap is replaced with new one. 8) * * More seriously: * 1. If rtt variance happened to be less 50msec, it is hallucination. * It cannot be less due to utterly erratic ACK generation made * at least by solaris and freebsd. "Erratic ACKs" has _nothing_ * to do with delayed acks, because at cwnd>2 true delack timeout * is invisible. Actually, Linux-2.4 also generates erratic * ACKs in some curcumstances. */ tp->rto = (tp->srtt >> 3) + tp->rttvar; /* 2. Fixups made earlier cannot be right. * If we do not estimate RTO correctly without them, * all the algo is pure shit and should be replaced * with correct one. It is exaclty, which we pretend to do. */ } /* NOTE: clamping at TCP_RTO_MIN is not required, current algo * guarantees that rto is higher. */ static __inline__ void tcp_bound_rto(struct tcp_opt *tp) { if (tp->rto > TCP_RTO_MAX) tp->rto = TCP_RTO_MAX; } /* Save metrics learned by this TCP session. This function is called only, when TCP finishes successfully i.e. when it enters TIME-WAIT or goes from LAST-ACK to CLOSE. */ void tcp_update_metrics(struct sock *sk) { struct tcp_opt *tp = tcp_sk(sk); struct dst_entry *dst = __sk_dst_get(sk); dst_confirm(dst); if (dst && (dst->flags&DST_HOST)) { int m; if (tp->backoff || !tp->srtt) { /* This session failed to estimate rtt. Why? * Probably, no packets returned in time. * Reset our results. */ if (!(dst_metric_locked(dst, RTAX_RTT))) dst->metrics[RTAX_RTT-1] = 0; return; } m = dst_metric(dst, RTAX_RTT) - tp->srtt; /* If newly calculated rtt larger than stored one, * store new one. Otherwise, use EWMA. Remember, * rtt overestimation is always better than underestimation. */ if (!(dst_metric_locked(dst, RTAX_RTT))) { if (m <= 0) dst->metrics[RTAX_RTT-1] = tp->srtt; else dst->metrics[RTAX_RTT-1] -= (m>>3); } if (!(dst_metric_locked(dst, RTAX_RTTVAR))) { if (m < 0) m = -m; /* Scale deviation to rttvar fixed point */ m >>= 1; if (m < tp->mdev) m = tp->mdev; if (m >= dst_metric(dst, RTAX_RTTVAR)) dst->metrics[RTAX_RTTVAR-1] = m; else dst->metrics[RTAX_RTTVAR-1] -= (dst->metrics[RTAX_RTTVAR-1] - m)>>2; } if (tp->snd_ssthresh >= 0xFFFF) { /* Slow start still did not finish. */ if (dst_metric(dst, RTAX_SSTHRESH) && !dst_metric_locked(dst, RTAX_SSTHRESH) && (tp->snd_cwnd >> 1) > dst_metric(dst, RTAX_SSTHRESH)) dst->metrics[RTAX_SSTHRESH-1] = tp->snd_cwnd >> 1; if (!dst_metric_locked(dst, RTAX_CWND) && tp->snd_cwnd > dst_metric(dst, RTAX_CWND)) dst->metrics[RTAX_CWND-1] = tp->snd_cwnd; } else if (tp->snd_cwnd > tp->snd_ssthresh && tp->ca_state == TCP_CA_Open) { /* Cong. avoidance phase, cwnd is reliable. */ if (!dst_metric_locked(dst, RTAX_SSTHRESH)) dst->metrics[RTAX_SSTHRESH-1] = max(tp->snd_cwnd >> 1, tp->snd_ssthresh); if (!dst_metric_locked(dst, RTAX_CWND)) dst->metrics[RTAX_CWND-1] = (dst->metrics[RTAX_CWND-1] + tp->snd_cwnd) >> 1; } else { /* Else slow start did not finish, cwnd is non-sense, ssthresh may be also invalid. */ if (!dst_metric_locked(dst, RTAX_CWND)) dst->metrics[RTAX_CWND-1] = (dst->metrics[RTAX_CWND-1] + tp->snd_ssthresh) >> 1; if (dst->metrics[RTAX_SSTHRESH-1] && !dst_metric_locked(dst, RTAX_SSTHRESH) && tp->snd_ssthresh > dst->metrics[RTAX_SSTHRESH-1]) dst->metrics[RTAX_SSTHRESH-1] = tp->snd_ssthresh; } if (!dst_metric_locked(dst, RTAX_REORDERING)) { if (dst->metrics[RTAX_REORDERING-1] < tp->reordering && tp->reordering != sysctl_tcp_reordering) dst->metrics[RTAX_REORDERING-1] = tp->reordering; } } } /* Numbers are taken from RFC2414. */ __u32 tcp_init_cwnd(struct tcp_opt *tp, struct dst_entry *dst) { __u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0); if (!cwnd) { if (tp->mss_cache > 1460) cwnd = 2; else cwnd = (tp->mss_cache > 1095) ? 3 : 4; } return min_t(__u32, cwnd, tp->snd_cwnd_clamp); } /* Initialize metrics on socket. */ static void tcp_init_metrics(struct sock *sk) { struct tcp_opt *tp = tcp_sk(sk); struct dst_entry *dst = __sk_dst_get(sk); if (dst == NULL) goto reset; dst_confirm(dst); if (dst_metric_locked(dst, RTAX_CWND)) tp->snd_cwnd_clamp = dst_metric(dst, RTAX_CWND); if (dst_metric(dst, RTAX_SSTHRESH)) { tp->snd_ssthresh = dst_metric(dst, RTAX_SSTHRESH); if (tp->snd_ssthresh > tp->snd_cwnd_clamp) tp->snd_ssthresh = tp->snd_cwnd_clamp; } if (dst_metric(dst, RTAX_REORDERING) && tp->reordering != dst_metric(dst, RTAX_REORDERING)) { tp->sack_ok &= ~2; tp->reordering = dst_metric(dst, RTAX_REORDERING); } if (dst_metric(dst, RTAX_RTT) == 0) goto reset; if (!tp->srtt && dst_metric(dst, RTAX_RTT) < (TCP_TIMEOUT_INIT << 3)) goto reset; /* Initial rtt is determined from SYN,SYN-ACK. * The segment is small and rtt may appear much * less than real one. Use per-dst memory * to make it more realistic. * * A bit of theory. RTT is time passed after "normal" sized packet * is sent until it is ACKed. In normal curcumstances sending small * packets force peer to delay ACKs and calculation is correct too. * The algorithm is adaptive and, provided we follow specs, it * NEVER underestimate RTT. BUT! If peer tries to make some clever * tricks sort of "quick acks" for time long enough to decrease RTT * to low value, and then abruptly stops to do it and starts to delay * ACKs, wait for troubles. */ if (dst_metric(dst, RTAX_RTT) > tp->srtt) tp->srtt = dst_metric(dst, RTAX_RTT); if (dst_metric(dst, RTAX_RTTVAR) > tp->mdev) { tp->mdev = dst_metric(dst, RTAX_RTTVAR); tp->mdev_max = tp->rttvar = max(tp->mdev, TCP_RTO_MIN); } tcp_set_rto(tp); tcp_bound_rto(tp); if (tp->rto < TCP_TIMEOUT_INIT && !tp->saw_tstamp) goto reset; tp->snd_cwnd = tcp_init_cwnd(tp, dst); tp->snd_cwnd_stamp = tcp_time_stamp; return; reset: /* Play conservative. If timestamps are not * supported, TCP will fail to recalculate correct * rtt, if initial rto is too small. FORGET ALL AND RESET! */ if (!tp->saw_tstamp && tp->srtt) { tp->srtt = 0; tp->mdev = tp->mdev_max = tp->rttvar = TCP_TIMEOUT_INIT; tp->rto = TCP_TIMEOUT_INIT; } } static void tcp_update_reordering(struct tcp_opt *tp, int metric, int ts) { if (metric > tp->reordering) { tp->reordering = min(TCP_MAX_REORDERING, metric); /* This exciting event is worth to be remembered. 8) */ if (ts) NET_INC_STATS_BH(TCPTSReorder); else if (IsReno(tp)) NET_INC_STATS_BH(TCPRenoReorder); else if (IsFack(tp)) NET_INC_STATS_BH(TCPFACKReorder); else NET_INC_STATS_BH(TCPSACKReorder); #if FASTRETRANS_DEBUG > 1 printk(KERN_DEBUG "Disorder%d %d %u f%u s%u rr%d\n", tp->sack_ok, tp->ca_state, tp->reordering, tp->fackets_out, tp->sacked_out, tp->undo_marker ? tp->undo_retrans : 0); #endif /* Disable FACK yet. */ tp->sack_ok &= ~2; } } /* This procedure tags the retransmission queue when SACKs arrive. * * We have three tag bits: SACKED(S), RETRANS(R) and LOST(L). * Packets in queue with these bits set are counted in variables * sacked_out, retrans_out and lost_out, correspondingly. * * Valid combinations are: * Tag InFlight Description * 0 1 - orig segment is in flight. * S 0 - nothing flies, orig reached receiver. * L 0 - nothing flies, orig lost by net. * R 2 - both orig and retransmit are in flight. * L|R 1 - orig is lost, retransmit is in flight. * S|R 1 - orig reached receiver, retrans is still in flight. * (L|S|R is logically valid, it could occur when L|R is sacked, * but it is equivalent to plain S and code short-curcuits it to S. * L|S is logically invalid, it would mean -1 packet in flight 8)) * * These 6 states form finite state machine, controlled by the following events: * 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue()) * 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue()) * 3. Loss detection event of one of three flavors: * A. Scoreboard estimator decided the packet is lost. * A'. Reno "three dupacks" marks head of queue lost. * A''. Its FACK modfication, head until snd.fack is lost. * B. SACK arrives sacking data transmitted after never retransmitted * hole was sent out. * C. SACK arrives sacking SND.NXT at the moment, when the * segment was retransmitted. * 4. D-SACK added new rule: D-SACK changes any tag to S. * * It is pleasant to note, that state diagram turns out to be commutative, * so that we are allowed not to be bothered by order of our actions, * when multiple events arrive simultaneously. (see the function below). * * Reordering detection. * -------------------- * Reordering metric is maximal distance, which a packet can be displaced * in packet stream. With SACKs we can estimate it: * * 1. SACK fills old hole and the corresponding segment was not * ever retransmitted -> reordering. Alas, we cannot use it * when segment was retransmitted. * 2. The last flaw is solved with D-SACK. D-SACK arrives * for retransmitted and already SACKed segment -> reordering.. * Both of these heuristics are not used in Loss state, when we cannot * account for retransmits accurately. */ static int tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, u32 prior_snd_una) { struct tcp_opt *tp = tcp_sk(sk); unsigned char *ptr = ack_skb->h.raw + TCP_SKB_CB(ack_skb)->sacked; struct tcp_sack_block *sp = (struct tcp_sack_block *)(ptr+2); int num_sacks = (ptr[1] - TCPOLEN_SACK_BASE)>>3; int reord = tp->packets_out; int prior_fackets; u32 lost_retrans = 0; int flag = 0; int i; /* So, SACKs for already sent large segments will be lost. * Not good, but alternative is to resegment the queue. */ if (sk->sk_route_caps & NETIF_F_TSO) { sk->sk_route_caps &= ~NETIF_F_TSO; sk->sk_no_largesend = 1; tp->mss_cache = tp->mss_cache_std; } if (!tp->sacked_out) tp->fackets_out = 0; prior_fackets = tp->fackets_out; for (i=0; i<num_sacks; i++, sp++) { struct sk_buff *skb; __u32 start_seq = ntohl(sp->start_seq); __u32 end_seq = ntohl(sp->end_seq); int fack_count = 0; int dup_sack = 0; /* Check for D-SACK. */ if (i == 0) { u32 ack = TCP_SKB_CB(ack_skb)->ack_seq; if (before(start_seq, ack)) { dup_sack = 1; tp->sack_ok |= 4; NET_INC_STATS_BH(TCPDSACKRecv); } else if (num_sacks > 1 && !after(end_seq, ntohl(sp[1].end_seq)) && !before(start_seq, ntohl(sp[1].start_seq))) { dup_sack = 1; tp->sack_ok |= 4; NET_INC_STATS_BH(TCPDSACKOfoRecv); } /* D-SACK for already forgotten data... * Do dumb counting. */ if (dup_sack && !after(end_seq, prior_snd_una) && after(end_seq, tp->undo_marker)) tp->undo_retrans--; /* Eliminate too old ACKs, but take into * account more or less fresh ones, they can * contain valid SACK info. */ if (before(ack, prior_snd_una - tp->max_window)) return 0; } /* Event "B" in the comment above. */ if (after(end_seq, tp->high_seq)) flag |= FLAG_DATA_LOST; for_retrans_queue(skb, sk, tp) { u8 sacked = TCP_SKB_CB(skb)->sacked; int in_sack; /* The retransmission queue is always in order, so * we can short-circuit the walk early. */ if(!before(TCP_SKB_CB(skb)->seq, end_seq)) break; fack_count++; in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) && !before(end_seq, TCP_SKB_CB(skb)->end_seq); /* Account D-SACK for retransmitted packet. */ if ((dup_sack && in_sack) && (sacked & TCPCB_RETRANS) && after(TCP_SKB_CB(skb)->end_seq, tp->undo_marker)) tp->undo_retrans--; /* The frame is ACKed. */ if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una)) { if (sacked&TCPCB_RETRANS) { if ((dup_sack && in_sack) && (sacked&TCPCB_SACKED_ACKED)) reord = min(fack_count, reord); } else { /* If it was in a hole, we detected reordering. */ if (fack_count < prior_fackets && !(sacked&TCPCB_SACKED_ACKED)) reord = min(fack_count, reord); } /* Nothing to do; acked frame is about to be dropped. */ continue; } if ((sacked&TCPCB_SACKED_RETRANS) && after(end_seq, TCP_SKB_CB(skb)->ack_seq) && (!lost_retrans || after(end_seq, lost_retrans))) lost_retrans = end_seq; if (!in_sack) continue; if (!(sacked&TCPCB_SACKED_ACKED)) { if (sacked & TCPCB_SACKED_RETRANS) { /* If the segment is not tagged as lost, * we do not clear RETRANS, believing * that retransmission is still in flight. */ if (sacked & TCPCB_LOST) { TCP_SKB_CB(skb)->sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS); tp->lost_out--; tp->retrans_out--; } } else { /* New sack for not retransmitted frame, * which was in hole. It is reordering. */ if (!(sacked & TCPCB_RETRANS) && fack_count < prior_fackets) reord = min(fack_count, reord); if (sacked & TCPCB_LOST) { TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST; tp->lost_out--; } } TCP_SKB_CB(skb)->sacked |= TCPCB_SACKED_ACKED; flag |= FLAG_DATA_SACKED; tp->sacked_out++; if (fack_count > tp->fackets_out) tp->fackets_out = fack_count; } else { if (dup_sack && (sacked&TCPCB_RETRANS)) reord = min(fack_count, reord); } /* D-SACK. We can detect redundant retransmission * in S|R and plain R frames and clear it. * undo_retrans is decreased above, L|R frames * are accounted above as well. */ if (dup_sack && (TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_RETRANS)) { TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS; tp->retrans_out--; } } } /* Check for lost retransmit. This superb idea is * borrowed from "ratehalving". Event "C". * Later note: FACK people cheated me again 8), * we have to account for reordering! Ugly, * but should help. */ if (lost_retrans && tp->ca_state == TCP_CA_Recovery) { struct sk_buff *skb; for_retrans_queue(skb, sk, tp) { if (after(TCP_SKB_CB(skb)->seq, lost_retrans)) break; if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una)) continue; if ((TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_RETRANS) && after(lost_retrans, TCP_SKB_CB(skb)->ack_seq) && (IsFack(tp) || !before(lost_retrans, TCP_SKB_CB(skb)->ack_seq + tp->reordering * tp->mss_cache))) { TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS; tp->retrans_out--; if (!(TCP_SKB_CB(skb)->sacked&(TCPCB_LOST|TCPCB_SACKED_ACKED))) { tp->lost_out++; TCP_SKB_CB(skb)->sacked |= TCPCB_LOST; flag |= FLAG_DATA_SACKED; NET_INC_STATS_BH(TCPLostRetransmit); } } } } tp->left_out = tp->sacked_out + tp->lost_out; if (reord < tp->fackets_out && tp->ca_state != TCP_CA_Loss) tcp_update_reordering(tp, (tp->fackets_out + 1) - reord, 0); #if FASTRETRANS_DEBUG > 0 BUG_TRAP((int)tp->sacked_out >= 0); BUG_TRAP((int)tp->lost_out >= 0); BUG_TRAP((int)tp->retrans_out >= 0); BUG_TRAP((int)tcp_packets_in_flight(tp) >= 0); #endif return flag; } /* RTO occurred, but do not yet enter loss state. Instead, transmit two new * segments to see from the next ACKs whether any data was really missing. * If the RTO was spurious, new ACKs should arrive. */ void tcp_enter_frto(struct sock *sk) { struct tcp_opt *tp = tcp_sk(sk); struct sk_buff *skb; tp->frto_counter = 1; if (tp->ca_state <= TCP_CA_Disorder || tp->snd_una == tp->high_seq || (tp->ca_state == TCP_CA_Loss && !tp->retransmits)) { tp->prior_ssthresh = tcp_current_ssthresh(tp); tp->snd_ssthresh = tcp_recalc_ssthresh(tp); } /* Have to clear retransmission markers here to keep the bookkeeping * in shape, even though we are not yet in Loss state. * If something was really lost, it is eventually caught up * in tcp_enter_frto_loss. */ tp->retrans_out = 0; tp->undo_marker = tp->snd_una; tp->undo_retrans = 0; for_retrans_queue(skb, sk, tp) { TCP_SKB_CB(skb)->sacked &= ~TCPCB_RETRANS; } tcp_sync_left_out(tp); tp->ca_state = TCP_CA_Open; tp->frto_highmark = tp->snd_nxt; } /* Enter Loss state after F-RTO was applied. Dupack arrived after RTO, * which indicates that we should follow the traditional RTO recovery, * i.e. mark everything lost and do go-back-N retransmission. */ void tcp_enter_frto_loss(struct sock *sk) { struct tcp_opt *tp = tcp_sk(sk); struct sk_buff *skb; int cnt = 0; tp->sacked_out = 0; tp->lost_out = 0; tp->fackets_out = 0; for_retrans_queue(skb, sk, tp) { cnt++; TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST; if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED)) { /* Do not mark those segments lost that were * forward transmitted after RTO */ if(!after(TCP_SKB_CB(skb)->end_seq, tp->frto_highmark)) { TCP_SKB_CB(skb)->sacked |= TCPCB_LOST; tp->lost_out++; } } else { tp->sacked_out++; tp->fackets_out = cnt; } } tcp_sync_left_out(tp); tp->snd_cwnd = tp->frto_counter + tcp_packets_in_flight(tp)+1; tp->snd_cwnd_cnt = 0; tp->snd_cwnd_stamp = tcp_time_stamp; tp->undo_marker = 0; tp->frto_counter = 0; tp->reordering = min_t(unsigned int, tp->reordering, sysctl_tcp_reordering); tp->ca_state = TCP_CA_Loss; tp->high_seq = tp->frto_highmark; TCP_ECN_queue_cwr(tp); } void tcp_clear_retrans(struct tcp_opt *tp) { tp->left_out = 0; tp->retrans_out = 0; tp->fackets_out = 0; tp->sacked_out = 0; tp->lost_out = 0; tp->undo_marker = 0; tp->undo_retrans = 0; } /* Enter Loss state. If "how" is not zero, forget all SACK information * and reset tags completely, otherwise preserve SACKs. If receiver * dropped its ofo queue, we will know this due to reneging detection. */ void tcp_enter_loss(struct sock *sk, int how) { struct tcp_opt *tp = tcp_sk(sk); struct sk_buff *skb; int cnt = 0; /* Reduce ssthresh if it has not yet been made inside this window. */ if (tp->ca_state <= TCP_CA_Disorder || tp->snd_una == tp->high_seq || (tp->ca_state == TCP_CA_Loss && !tp->retransmits)) { tp->prior_ssthresh = tcp_current_ssthresh(tp); tp->snd_ssthresh = tcp_recalc_ssthresh(tp); } tp->snd_cwnd = 1; tp->snd_cwnd_cnt = 0; tp->snd_cwnd_stamp = tcp_time_stamp; tcp_clear_retrans(tp); /* Push undo marker, if it was plain RTO and nothing * was retransmitted. */ if (!how) tp->undo_marker = tp->snd_una; for_retrans_queue(skb, sk, tp) { cnt++; if (TCP_SKB_CB(skb)->sacked&TCPCB_RETRANS) tp->undo_marker = 0; TCP_SKB_CB(skb)->sacked &= (~TCPCB_TAGBITS)|TCPCB_SACKED_ACKED; if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED) || how) { TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED; TCP_SKB_CB(skb)->sacked |= TCPCB_LOST; tp->lost_out++; } else { tp->sacked_out++; tp->fackets_out = cnt; } } tcp_sync_left_out(tp); tp->reordering = min_t(unsigned int, tp->reordering, sysctl_tcp_reordering); tp->ca_state = TCP_CA_Loss; tp->high_seq = tp->snd_nxt; TCP_ECN_queue_cwr(tp); } static int tcp_check_sack_reneging(struct sock *sk, struct tcp_opt *tp) { struct sk_buff *skb; /* If ACK arrived pointing to a remembered SACK, * it means that our remembered SACKs do not reflect * real state of receiver i.e. * receiver _host_ is heavily congested (or buggy). * Do processing similar to RTO timeout. */ if ((skb = skb_peek(&sk->sk_write_queue)) != NULL && (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) { NET_INC_STATS_BH(TCPSACKReneging); tcp_enter_loss(sk, 1); tp->retransmits++; tcp_retransmit_skb(sk, skb_peek(&sk->sk_write_queue)); tcp_reset_xmit_timer(sk, TCP_TIME_RETRANS, tp->rto); return 1; } return 0; } static inline int tcp_fackets_out(struct tcp_opt *tp) { return IsReno(tp) ? tp->sacked_out+1 : tp->fackets_out; } static inline int tcp_skb_timedout(struct tcp_opt *tp, struct sk_buff *skb) { return (tcp_time_stamp - TCP_SKB_CB(skb)->when > tp->rto); } static inline int tcp_head_timedout(struct sock *sk, struct tcp_opt *tp) { return tp->packets_out && tcp_skb_timedout(tp, skb_peek(&sk->sk_write_queue)); } /* Linux NewReno/SACK/FACK/ECN state machine. * -------------------------------------- * * "Open" Normal state, no dubious events, fast path. * "Disorder" In all the respects it is "Open", * but requires a bit more attention. It is entered when * we see some SACKs or dupacks. It is split of "Open" * mainly to move some processing from fast path to slow one. * "CWR" CWND was reduced due to some Congestion Notification event. * It can be ECN, ICMP source quench, local device congestion. * "Recovery" CWND was reduced, we are fast-retransmitting. * "Loss" CWND was reduced due to RTO timeout or SACK reneging. * * tcp_fastretrans_alert() is entered: * - each incoming ACK, if state is not "Open" * - when arrived ACK is unusual, namely: * * SACK * * Duplicate ACK. * * ECN ECE. * * Counting packets in flight is pretty simple. * * in_flight = packets_out - left_out + retrans_out * * packets_out is SND.NXT-SND.UNA counted in packets. * * retrans_out is number of retransmitted segments. * * left_out is number of segments left network, but not ACKed yet. * * left_out = sacked_out + lost_out * * sacked_out: Packets, which arrived to receiver out of order * and hence not ACKed. With SACKs this number is simply * amount of SACKed data. Even without SACKs * it is easy to give pretty reliable estimate of this number, * counting duplicate ACKs. * * lost_out: Packets lost by network. TCP has no explicit * "loss notification" feedback from network (for now). * It means that this number can be only _guessed_. * Actually, it is the heuristics to predict lossage that * distinguishes different algorithms. * * F.e. after RTO, when all the queue is considered as lost, * lost_out = packets_out and in_flight = retrans_out. * * Essentially, we have now two algorithms counting * lost packets. * * FACK: It is the simplest heuristics. As soon as we decided * that something is lost, we decide that _all_ not SACKed * packets until the most forward SACK are lost. I.e. * lost_out = fackets_out - sacked_out and left_out = fackets_out. * It is absolutely correct estimate, if network does not reorder * packets. And it loses any connection to reality when reordering * takes place. We use FACK by default until reordering * is suspected on the path to this destination. * * NewReno: when Recovery is entered, we assume that one segment * is lost (classic Reno). While we are in Recovery and * a partial ACK arrives, we assume that one more packet * is lost (NewReno). This heuristics are the same in NewReno * and SACK. * * Imagine, that's all! Forget about all this shamanism about CWND inflation * deflation etc. CWND is real congestion window, never inflated, changes * only according to classic VJ rules. * * Really tricky (and requiring careful tuning) part of algorithm * is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue(). * The first determines the moment _when_ we should reduce CWND and, * hence, slow down forward transmission. In fact, it determines the moment * when we decide that hole is caused by loss, rather than by a reorder. * * tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill * holes, caused by lost packets. * * And the most logically complicated part of algorithm is undo * heuristics. We detect false retransmits due to both too early * fast retransmit (reordering) and underestimated RTO, analyzing * timestamps and D-SACKs. When we detect that some segments were * retransmitted by mistake and CWND reduction was wrong, we undo * window reduction and abort recovery phase. This logic is hidden * inside several functions named tcp_try_undo_<something>. */ /* This function decides, when we should leave Disordered state * and enter Recovery phase, reducing congestion window. * * Main question: may we further continue forward transmission * with the same cwnd? */ static int tcp_time_to_recover(struct sock *sk, struct tcp_opt *tp) { /* Trick#1: The loss is proven. */ if (tp->lost_out) return 1; /* Not-A-Trick#2 : Classic rule... */ if (tcp_fackets_out(tp) > tp->reordering) return 1; /* Trick#3 : when we use RFC2988 timer restart, fast * retransmit can be triggered by timeout of queue head. */ if (tcp_head_timedout(sk, tp)) return 1; /* Trick#4: It is still not OK... But will it be useful to delay * recovery more? */ if (tp->packets_out <= tp->reordering && tp->sacked_out >= max_t(__u32, tp->packets_out/2, sysctl_tcp_reordering) && !tcp_may_send_now(sk, tp)) { /* We have nothing to send. This connection is limited * either by receiver window or by application. */ return 1; } return 0; } /* If we receive more dupacks than we expected counting segments * in assumption of absent reordering, interpret this as reordering. * The only another reason could be bug in receiver TCP. */ static void tcp_check_reno_reordering(struct tcp_opt *tp, int addend) { u32 holes; holes = max(tp->lost_out, 1U); holes = min(holes, tp->packets_out); if (tp->sacked_out + holes > tp->packets_out) { tp->sacked_out = tp->packets_out - holes; tcp_update_reordering(tp, tp->packets_out+addend, 0); } } /* Emulate SACKs for SACKless connection: account for a new dupack. */ static void tcp_add_reno_sack(struct tcp_opt *tp) { ++tp->sacked_out; tcp_check_reno_reordering(tp, 0); tcp_sync_left_out(tp); } /* Account for ACK, ACKing some data in Reno Recovery phase. */ static void tcp_remove_reno_sacks(struct sock *sk, struct tcp_opt *tp, int acked) { if (acked > 0) { /* One ACK acked hole. The rest eat duplicate ACKs. */ if (acked-1 >= tp->sacked_out) tp->sacked_out = 0; else tp->sacked_out -= acked-1; } tcp_check_reno_reordering(tp, acked); tcp_sync_left_out(tp); } static inline void tcp_reset_reno_sack(struct tcp_opt *tp) { tp->sacked_out = 0; tp->left_out = tp->lost_out; } /* Mark head of queue up as lost. */ static void tcp_mark_head_lost(struct sock *sk, struct tcp_opt *tp, int packets, u32 high_seq) { struct sk_buff *skb; int cnt = packets; BUG_TRAP(cnt <= tp->packets_out); for_retrans_queue(skb, sk, tp) { if (--cnt < 0 || after(TCP_SKB_CB(skb)->end_seq, high_seq)) break; if (!(TCP_SKB_CB(skb)->sacked&TCPCB_TAGBITS)) { TCP_SKB_CB(skb)->sacked |= TCPCB_LOST; tp->lost_out++; } } tcp_sync_left_out(tp); } /* Account newly detected lost packet(s) */ static void tcp_update_scoreboard(struct sock *sk, struct tcp_opt *tp) { if (IsFack(tp)) { int lost = tp->fackets_out - tp->reordering; if (lost <= 0) lost = 1; tcp_mark_head_lost(sk, tp, lost, tp->high_seq); } else { tcp_mark_head_lost(sk, tp, 1, tp->high_seq); } /* New heuristics: it is possible only after we switched * to restart timer each time when something is ACKed. * Hence, we can detect timed out packets during fast * retransmit without falling to slow start. */ if (tcp_head_timedout(sk, tp)) { struct sk_buff *skb; for_retrans_queue(skb, sk, tp) { if (tcp_skb_timedout(tp, skb) && !(TCP_SKB_CB(skb)->sacked&TCPCB_TAGBITS)) { TCP_SKB_CB(skb)->sacked |= TCPCB_LOST; tp->lost_out++; } } tcp_sync_left_out(tp); } } /* CWND moderation, preventing bursts due to too big ACKs * in dubious situations. */ static __inline__ void tcp_moderate_cwnd(struct tcp_opt *tp) { tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp)+tcp_max_burst(tp)); tp->snd_cwnd_stamp = tcp_time_stamp; } /* Decrease cwnd each second ack. */ static void tcp_cwnd_down(struct tcp_opt *tp) { int decr = tp->snd_cwnd_cnt + 1; tp->snd_cwnd_cnt = decr&1; decr >>= 1; if (decr && tp->snd_cwnd > tp->snd_ssthresh/2) tp->snd_cwnd -= decr; tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp)+1); tp->snd_cwnd_stamp = tcp_time_stamp; } /* Nothing was retransmitted or returned timestamp is less * than timestamp of the first retransmission. */ static __inline__ int tcp_packet_delayed(struct tcp_opt *tp) { return !tp->retrans_stamp || (tp->saw_tstamp && tp->rcv_tsecr && (__s32)(tp->rcv_tsecr - tp->retrans_stamp) < 0); } /* Undo procedures. */ #if FASTRETRANS_DEBUG > 1 static void DBGUNDO(struct sock *sk, struct tcp_opt *tp, const char *msg) { struct inet_opt *inet = inet_sk(sk); printk(KERN_DEBUG "Undo %s %u.%u.%u.%u/%u c%u l%u ss%u/%u p%u\n", msg, NIPQUAD(inet->daddr), ntohs(inet->dport), tp->snd_cwnd, tp->left_out, tp->snd_ssthresh, tp->prior_ssthresh, tp->packets_out); } #else #define DBGUNDO(x...) do { } while (0) #endif static void tcp_undo_cwr(struct tcp_opt *tp, int undo) { if (tp->prior_ssthresh) { tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh<<1); if (undo && tp->prior_ssthresh > tp->snd_ssthresh) { tp->snd_ssthresh = tp->prior_ssthresh; TCP_ECN_withdraw_cwr(tp); } } else { tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh); } tcp_moderate_cwnd(tp); tp->snd_cwnd_stamp = tcp_time_stamp; } static inline int tcp_may_undo(struct tcp_opt *tp) { return tp->undo_marker && (!tp->undo_retrans || tcp_packet_delayed(tp)); } /* People celebrate: "We love our President!" */ static int tcp_try_undo_recovery(struct sock *sk, struct tcp_opt *tp) { if (tcp_may_undo(tp)) { /* Happy end! We did not retransmit anything * or our original transmission succeeded. */ DBGUNDO(sk, tp, tp->ca_state == TCP_CA_Loss ? "loss" : "retrans"); tcp_undo_cwr(tp, 1); if (tp->ca_state == TCP_CA_Loss) NET_INC_STATS_BH(TCPLossUndo); else NET_INC_STATS_BH(TCPFullUndo); tp->undo_marker = 0; } if (tp->snd_una == tp->high_seq && IsReno(tp)) { /* Hold old state until something *above* high_seq * is ACKed. For Reno it is MUST to prevent false * fast retransmits (RFC2582). SACK TCP is safe. */ tcp_moderate_cwnd(tp); return 1; } tp->ca_state = TCP_CA_Open; return 0; } /* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */ static void tcp_try_undo_dsack(struct sock *sk, struct tcp_opt *tp) { if (tp->undo_marker && !tp->undo_retrans) { DBGUNDO(sk, tp, "D-SACK"); tcp_undo_cwr(tp, 1); tp->undo_marker = 0; NET_INC_STATS_BH(TCPDSACKUndo); } } /* Undo during fast recovery after partial ACK. */ static int tcp_try_undo_partial(struct sock *sk, struct tcp_opt *tp, int acked) { /* Partial ACK arrived. Force Hoe's retransmit. */ int failed = IsReno(tp) || tp->fackets_out>tp->reordering; if (tcp_may_undo(tp)) { /* Plain luck! Hole if filled with delayed * packet, rather than with a retransmit. */ if (tp->retrans_out == 0) tp->retrans_stamp = 0; tcp_update_reordering(tp, tcp_fackets_out(tp)+acked, 1); DBGUNDO(sk, tp, "Hoe"); tcp_undo_cwr(tp, 0); NET_INC_STATS_BH(TCPPartialUndo); /* So... Do not make Hoe's retransmit yet. * If the first packet was delayed, the rest * ones are most probably delayed as well. */ failed = 0; } return failed; } /* Undo during loss recovery after partial ACK. */ static int tcp_try_undo_loss(struct sock *sk, struct tcp_opt *tp) { if (tcp_may_undo(tp)) { struct sk_buff *skb; for_retrans_queue(skb, sk, tp) { TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST; } DBGUNDO(sk, tp, "partial loss"); tp->lost_out = 0; tp->left_out = tp->sacked_out; tcp_undo_cwr(tp, 1); NET_INC_STATS_BH(TCPLossUndo); tp->retransmits = 0; tp->undo_marker = 0; if (!IsReno(tp)) tp->ca_state = TCP_CA_Open; return 1; } return 0; } static __inline__ void tcp_complete_cwr(struct tcp_opt *tp) { tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh); tp->snd_cwnd_stamp = tcp_time_stamp; } static void tcp_try_to_open(struct sock *sk, struct tcp_opt *tp, int flag) { tp->left_out = tp->sacked_out; if (tp->retrans_out == 0) tp->retrans_stamp = 0; if (flag&FLAG_ECE) tcp_enter_cwr(tp); if (tp->ca_state != TCP_CA_CWR) { int state = TCP_CA_Open; if (tp->left_out || tp->retrans_out || tp->undo_marker) state = TCP_CA_Disorder; if (tp->ca_state != state) { tp->ca_state = state; tp->high_seq = tp->snd_nxt; } tcp_moderate_cwnd(tp); } else { tcp_cwnd_down(tp); } } /* Process an event, which can update packets-in-flight not trivially. * Main goal of this function is to calculate new estimate for left_out, * taking into account both packets sitting in receiver's buffer and * packets lost by network. * * Besides that it does CWND reduction, when packet loss is detected * and changes state of machine. * * It does _not_ decide what to send, it is made in function * tcp_xmit_retransmit_queue(). */ static void tcp_fastretrans_alert(struct sock *sk, u32 prior_snd_una, int prior_packets, int flag) { struct tcp_opt *tp = tcp_sk(sk); int is_dupack = (tp->snd_una == prior_snd_una && !(flag&FLAG_NOT_DUP)); /* Some technical things: * 1. Reno does not count dupacks (sacked_out) automatically. */ if (!tp->packets_out) tp->sacked_out = 0; /* 2. SACK counts snd_fack in packets inaccurately. */ if (tp->sacked_out == 0) tp->fackets_out = 0; /* Now state machine starts. * A. ECE, hence prohibit cwnd undoing, the reduction is required. */ if (flag&FLAG_ECE) tp->prior_ssthresh = 0; /* B. In all the states check for reneging SACKs. */ if (tp->sacked_out && tcp_check_sack_reneging(sk, tp)) return; /* C. Process data loss notification, provided it is valid. */ if ((flag&FLAG_DATA_LOST) && before(tp->snd_una, tp->high_seq) && tp->ca_state != TCP_CA_Open && tp->fackets_out > tp->reordering) { tcp_mark_head_lost(sk, tp, tp->fackets_out-tp->reordering, tp->high_seq); NET_INC_STATS_BH(TCPLoss); } /* D. Synchronize left_out to current state. */ tcp_sync_left_out(tp); /* E. Check state exit conditions. State can be terminated * when high_seq is ACKed. */ if (tp->ca_state == TCP_CA_Open) { if (!sysctl_tcp_frto) BUG_TRAP(tp->retrans_out == 0); tp->retrans_stamp = 0; } else if (!before(tp->snd_una, tp->high_seq)) { switch (tp->ca_state) { case TCP_CA_Loss: tp->retransmits = 0; if (tcp_try_undo_recovery(sk, tp)) return; break; case TCP_CA_CWR: /* CWR is to be held something *above* high_seq * is ACKed for CWR bit to reach receiver. */ if (tp->snd_una != tp->high_seq) { tcp_complete_cwr(tp); tp->ca_state = TCP_CA_Open; } break; case TCP_CA_Disorder: tcp_try_undo_dsack(sk, tp); if (!tp->undo_marker || /* For SACK case do not Open to allow to undo * catching for all duplicate ACKs. */ IsReno(tp) || tp->snd_una != tp->high_seq) { tp->undo_marker = 0; tp->ca_state = TCP_CA_Open; } break; case TCP_CA_Recovery: if (IsReno(tp)) tcp_reset_reno_sack(tp); if (tcp_try_undo_recovery(sk, tp)) return; tcp_complete_cwr(tp); break; } } /* F. Process state. */ switch (tp->ca_state) { case TCP_CA_Recovery: if (prior_snd_una == tp->snd_una) { if (IsReno(tp) && is_dupack) tcp_add_reno_sack(tp); } else { int acked = prior_packets - tp->packets_out; if (IsReno(tp)) tcp_remove_reno_sacks(sk, tp, acked); is_dupack = tcp_try_undo_partial(sk, tp, acked); } break; case TCP_CA_Loss: if (flag&FLAG_DATA_ACKED) tp->retransmits = 0; if (!tcp_try_undo_loss(sk, tp)) { tcp_moderate_cwnd(tp); tcp_xmit_retransmit_queue(sk); return; } if (tp->ca_state != TCP_CA_Open) return; /* Loss is undone; fall through to processing in Open state. */ default: if (IsReno(tp)) { if (tp->snd_una != prior_snd_una) tcp_reset_reno_sack(tp); if (is_dupack) tcp_add_reno_sack(tp); } if (tp->ca_state == TCP_CA_Disorder) tcp_try_undo_dsack(sk, tp); if (!tcp_time_to_recover(sk, tp)) { tcp_try_to_open(sk, tp, flag); return; } /* Otherwise enter Recovery state */ if (IsReno(tp)) NET_INC_STATS_BH(TCPRenoRecovery); else NET_INC_STATS_BH(TCPSackRecovery); tp->high_seq = tp->snd_nxt; tp->prior_ssthresh = 0; tp->undo_marker = tp->snd_una; tp->undo_retrans = tp->retrans_out; if (tp->ca_state < TCP_CA_CWR) { if (!(flag&FLAG_ECE)) tp->prior_ssthresh = tcp_current_ssthresh(tp); tp->snd_ssthresh = tcp_recalc_ssthresh(tp); TCP_ECN_queue_cwr(tp); } tp->snd_cwnd_cnt = 0; tp->ca_state = TCP_CA_Recovery; } if (is_dupack || tcp_head_timedout(sk, tp)) tcp_update_scoreboard(sk, tp); tcp_cwnd_down(tp); tcp_xmit_retransmit_queue(sk); } /* Read draft-ietf-tcplw-high-performance before mucking * with this code. (Superceeds RFC1323) */ static void tcp_ack_saw_tstamp(struct tcp_opt *tp, int flag) { __u32 seq_rtt; /* RTTM Rule: A TSecr value received in a segment is used to * update the averaged RTT measurement only if the segment * acknowledges some new data, i.e., only if it advances the * left edge of the send window. * * See draft-ietf-tcplw-high-performance-00, section 3.3. * 1998/04/10 Andrey V. Savochkin <saw@msu.ru> * * Changed: reset backoff as soon as we see the first valid sample. * If we do not, we get strongly overstimated rto. With timestamps * samples are accepted even from very old segments: f.e., when rtt=1 * increases to 8, we retransmit 5 times and after 8 seconds delayed * answer arrives rto becomes 120 seconds! If at least one of segments * in window is lost... Voila. --ANK (010210) */ seq_rtt = tcp_time_stamp - tp->rcv_tsecr; tcp_rtt_estimator(tp, seq_rtt); tcp_set_rto(tp); tp->backoff = 0; tcp_bound_rto(tp); } static void tcp_ack_no_tstamp(struct tcp_opt *tp, u32 seq_rtt, int flag) { /* We don't have a timestamp. Can only use * packets that are not retransmitted to determine * rtt estimates. Also, we must not reset the * backoff for rto until we get a non-retransmitted * packet. This allows us to deal with a situation * where the network delay has increased suddenly. * I.e. Karn's algorithm. (SIGCOMM '87, p5.) */ if (flag & FLAG_RETRANS_DATA_ACKED) return; tcp_rtt_estimator(tp, seq_rtt); tcp_set_rto(tp); tp->backoff = 0; tcp_bound_rto(tp); } static __inline__ void tcp_ack_update_rtt(struct tcp_opt *tp, int flag, s32 seq_rtt) { /* Note that peer MAY send zero echo. In this case it is ignored. (rfc1323) */ if (tp->saw_tstamp && tp->rcv_tsecr) tcp_ack_saw_tstamp(tp, flag); else if (seq_rtt >= 0) tcp_ack_no_tstamp(tp, seq_rtt, flag); } /* This is Jacobson's slow start and congestion avoidance. * SIGCOMM '88, p. 328. */ static __inline__ void tcp_cong_avoid(struct tcp_opt *tp) { if (tp->snd_cwnd <= tp->snd_ssthresh) { /* In "safe" area, increase. */ if (tp->snd_cwnd < tp->snd_cwnd_clamp) tp->snd_cwnd++; } else { /* In dangerous area, increase slowly. * In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd */ if (tp->snd_cwnd_cnt >= tp->snd_cwnd) { if (tp->snd_cwnd < tp->snd_cwnd_clamp) tp->snd_cwnd++; tp->snd_cwnd_cnt=0; } else tp->snd_cwnd_cnt++; } tp->snd_cwnd_stamp = tcp_time_stamp; } /* Restart timer after forward progress on connection. * RFC2988 recommends to restart timer to now+rto. */ static __inline__ void tcp_ack_packets_out(struct sock *sk, struct tcp_opt *tp) { if (tp->packets_out==0) { tcp_clear_xmit_timer(sk, TCP_TIME_RETRANS); } else { tcp_reset_xmit_timer(sk, TCP_TIME_RETRANS, tp->rto); } } /* Remove acknowledged frames from the retransmission queue. */ static int tcp_clean_rtx_queue(struct sock *sk) { struct tcp_opt *tp = tcp_sk(sk); struct sk_buff *skb; __u32 now = tcp_time_stamp; int acked = 0; __s32 seq_rtt = -1; while ((skb = skb_peek(&sk->sk_write_queue)) && skb != tp->send_head) { struct tcp_skb_cb *scb = TCP_SKB_CB(skb); __u8 sacked = scb->sacked; /* If our packet is before the ack sequence we can * discard it as it's confirmed to have arrived at * the other end. */ if (after(scb->end_seq, tp->snd_una)) break; /* Initial outgoing SYN's get put onto the write_queue * just like anything else we transmit. It is not * true data, and if we misinform our callers that * this ACK acks real data, we will erroneously exit * connection startup slow start one packet too * quickly. This is severely frowned upon behavior. */ if(!(scb->flags & TCPCB_FLAG_SYN)) { acked |= FLAG_DATA_ACKED; } else { acked |= FLAG_SYN_ACKED; tp->retrans_stamp = 0; } if (sacked) { if(sacked & TCPCB_RETRANS) { if(sacked & TCPCB_SACKED_RETRANS) tp->retrans_out--; acked |= FLAG_RETRANS_DATA_ACKED; seq_rtt = -1; } else if (seq_rtt < 0) seq_rtt = now - scb->when; if(sacked & TCPCB_SACKED_ACKED) tp->sacked_out--; if(sacked & TCPCB_LOST) tp->lost_out--; if(sacked & TCPCB_URG) { if (tp->urg_mode && !before(scb->end_seq, tp->snd_up)) tp->urg_mode = 0; } } else if (seq_rtt < 0) seq_rtt = now - scb->when; if (tp->fackets_out) tp->fackets_out--; tp->packets_out--; __skb_unlink(skb, skb->list); tcp_free_skb(sk, skb); } if (acked&FLAG_ACKED) { tcp_ack_update_rtt(tp, acked, seq_rtt); tcp_ack_packets_out(sk, tp); } #if FASTRETRANS_DEBUG > 0 BUG_TRAP((int)tp->sacked_out >= 0); BUG_TRAP((int)tp->lost_out >= 0); BUG_TRAP((int)tp->retrans_out >= 0); if (!tp->packets_out && tp->sack_ok) { if (tp->lost_out) { printk(KERN_DEBUG "Leak l=%u %d\n", tp->lost_out, tp->ca_state); tp->lost_out = 0; } if (tp->sacked_out) { printk(KERN_DEBUG "Leak s=%u %d\n", tp->sacked_out, tp->ca_state); tp->sacked_out = 0; } if (tp->retrans_out) { printk(KERN_DEBUG "Leak r=%u %d\n", tp->retrans_out, tp->ca_state); tp->retrans_out = 0; } } #endif return acked; } static void tcp_ack_probe(struct sock *sk) { struct tcp_opt *tp = tcp_sk(sk); /* Was it a usable window open? */ if (!after(TCP_SKB_CB(tp->send_head)->end_seq, tp->snd_una + tp->snd_wnd)) { tp->backoff = 0; tcp_clear_xmit_timer(sk, TCP_TIME_PROBE0); /* Socket must be waked up by subsequent tcp_data_snd_check(). * This function is not for random using! */ } else { tcp_reset_xmit_timer(sk, TCP_TIME_PROBE0, min(tp->rto << tp->backoff, TCP_RTO_MAX)); } } static __inline__ int tcp_ack_is_dubious(struct tcp_opt *tp, int flag) { return (!(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) || tp->ca_state != TCP_CA_Open); } static __inline__ int tcp_may_raise_cwnd(struct tcp_opt *tp, int flag) { return (!(flag & FLAG_ECE) || tp->snd_cwnd < tp->snd_ssthresh) && !((1<<tp->ca_state)&(TCPF_CA_Recovery|TCPF_CA_CWR)); } /* Check that window update is acceptable. * The function assumes that snd_una<=ack<=snd_next. */ static __inline__ int tcp_may_update_window(struct tcp_opt *tp, u32 ack, u32 ack_seq, u32 nwin) { return (after(ack, tp->snd_una) || after(ack_seq, tp->snd_wl1) || (ack_seq == tp->snd_wl1 && nwin > tp->snd_wnd)); } /* Update our send window. * * Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2 * and in FreeBSD. NetBSD's one is even worse.) is wrong. */ static int tcp_ack_update_window(struct sock *sk, struct tcp_opt *tp, struct sk_buff *skb, u32 ack, u32 ack_seq) { int flag = 0; u32 nwin = ntohs(skb->h.th->window) << tp->snd_wscale; if (tcp_may_update_window(tp, ack, ack_seq, nwin)) { flag |= FLAG_WIN_UPDATE; tcp_update_wl(tp, ack, ack_seq); if (tp->snd_wnd != nwin) { tp->snd_wnd = nwin; /* Note, it is the only place, where * fast path is recovered for sending TCP. */ tcp_fast_path_check(sk, tp); if (nwin > tp->max_window) { tp->max_window = nwin; tcp_sync_mss(sk, tp->pmtu_cookie); } } } tp->snd_una = ack; return flag; } static void tcp_process_frto(struct sock *sk, u32 prior_snd_una) { struct tcp_opt *tp = tcp_sk(sk); tcp_sync_left_out(tp); if (tp->snd_una == prior_snd_una || !before(tp->snd_una, tp->frto_highmark)) { /* RTO was caused by loss, start retransmitting in * go-back-N slow start */ tcp_enter_frto_loss(sk); return; } if (tp->frto_counter == 1) { /* First ACK after RTO advances the window: allow two new * segments out. */ tp->snd_cwnd = tcp_packets_in_flight(tp) + 2; } else { /* Also the second ACK after RTO advances the window. * The RTO was likely spurious. Reduce cwnd and continue * in congestion avoidance */ tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh); tcp_moderate_cwnd(tp); } /* F-RTO affects on two new ACKs following RTO. * At latest on third ACK the TCP behavor is back to normal. */ tp->frto_counter = (tp->frto_counter + 1) % 3; } /* This routine deals with incoming acks, but not outgoing ones. */ static int tcp_ack(struct sock *sk, struct sk_buff *skb, int flag) { struct tcp_opt *tp = tcp_sk(sk); u32 prior_snd_una = tp->snd_una; u32 ack_seq = TCP_SKB_CB(skb)->seq; u32 ack = TCP_SKB_CB(skb)->ack_seq; u32 prior_in_flight; int prior_packets; /* If the ack is newer than sent or older than previous acks * then we can probably ignore it. */ if (after(ack, tp->snd_nxt)) goto uninteresting_ack; if (before(ack, prior_snd_una)) goto old_ack; if (!(flag&FLAG_SLOWPATH) && after(ack, prior_snd_una)) { /* Window is constant, pure forward advance. * No more checks are required. * Note, we use the fact that SND.UNA>=SND.WL2. */ tcp_update_wl(tp, ack, ack_seq); tp->snd_una = ack; flag |= FLAG_WIN_UPDATE; NET_INC_STATS_BH(TCPHPAcks); } else { if (ack_seq != TCP_SKB_CB(skb)->end_seq) flag |= FLAG_DATA; else NET_INC_STATS_BH(TCPPureAcks); flag |= tcp_ack_update_window(sk, tp, skb, ack, ack_seq); if (TCP_SKB_CB(skb)->sacked) flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una); if (TCP_ECN_rcv_ecn_echo(tp, skb->h.th)) flag |= FLAG_ECE; } /* We passed data and got it acked, remove any soft error * log. Something worked... */ sk->sk_err_soft = 0; tp->rcv_tstamp = tcp_time_stamp; prior_packets = tp->packets_out; if (!prior_packets) goto no_queue; prior_in_flight = tcp_packets_in_flight(tp); /* See if we can take anything off of the retransmit queue. */ flag |= tcp_clean_rtx_queue(sk); if (tp->frto_counter) tcp_process_frto(sk, prior_snd_una); if (tcp_ack_is_dubious(tp, flag)) { /* Advanve CWND, if state allows this. */ if ((flag & FLAG_DATA_ACKED) && prior_in_flight >= tp->snd_cwnd && tcp_may_raise_cwnd(tp, flag)) tcp_cong_avoid(tp); tcp_fastretrans_alert(sk, prior_snd_una, prior_packets, flag); } else { if ((flag & FLAG_DATA_ACKED) && prior_in_flight >= tp->snd_cwnd) tcp_cong_avoid(tp); } if ((flag & FLAG_FORWARD_PROGRESS) || !(flag&FLAG_NOT_DUP)) dst_confirm(sk->sk_dst_cache); return 1; no_queue: tp->probes_out = 0; /* If this ack opens up a zero window, clear backoff. It was * being used to time the probes, and is probably far higher than * it needs to be for normal retransmission. */ if (tp->send_head) tcp_ack_probe(sk); return 1; old_ack: if (TCP_SKB_CB(skb)->sacked) tcp_sacktag_write_queue(sk, skb, prior_snd_una); uninteresting_ack: SOCK_DEBUG(sk, "Ack %u out of %u:%u\n", ack, tp->snd_una, tp->snd_nxt); return 0; } /* Look for tcp options. Normally only called on SYN and SYNACK packets. * But, this can also be called on packets in the established flow when * the fast version below fails. */ void tcp_parse_options(struct sk_buff *skb, struct tcp_opt *tp, int estab) { unsigned char *ptr; struct tcphdr *th = skb->h.th; int length=(th->doff*4)-sizeof(struct tcphdr); ptr = (unsigned char *)(th + 1); tp->saw_tstamp = 0; while(length>0) { int opcode=*ptr++; int opsize; switch (opcode) { case TCPOPT_EOL: return; case TCPOPT_NOP: /* Ref: RFC 793 section 3.1 */ length--; continue; default: opsize=*ptr++; if (opsize < 2) /* "silly options" */ return; if (opsize > length) return; /* don't parse partial options */ switch(opcode) { case TCPOPT_MSS: if(opsize==TCPOLEN_MSS && th->syn && !estab) { u16 in_mss = ntohs(*(__u16 *)ptr); if (in_mss) { if (tp->user_mss && tp->user_mss < in_mss) in_mss = tp->user_mss; tp->mss_clamp = in_mss; } } break; case TCPOPT_WINDOW: if(opsize==TCPOLEN_WINDOW && th->syn && !estab) if (sysctl_tcp_window_scaling) { tp->wscale_ok = 1; tp->snd_wscale = *(__u8 *)ptr; if(tp->snd_wscale > 14) { if(net_ratelimit()) printk("tcp_parse_options: Illegal window " "scaling value %d >14 received.", tp->snd_wscale); tp->snd_wscale = 14; } } break; case TCPOPT_TIMESTAMP: if(opsize==TCPOLEN_TIMESTAMP) { if ((estab && tp->tstamp_ok) || (!estab && sysctl_tcp_timestamps)) { tp->saw_tstamp = 1; tp->rcv_tsval = ntohl(*(__u32 *)ptr); tp->rcv_tsecr = ntohl(*(__u32 *)(ptr+4)); } } break; case TCPOPT_SACK_PERM: if(opsize==TCPOLEN_SACK_PERM && th->syn && !estab) { if (sysctl_tcp_sack) { tp->sack_ok = 1; tcp_sack_reset(tp); } } break; case TCPOPT_SACK: if((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) && !((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) && tp->sack_ok) { TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th; } }; ptr+=opsize-2; length-=opsize; }; } } /* Fast parse options. This hopes to only see timestamps. * If it is wrong it falls back on tcp_parse_options(). */ static __inline__ int tcp_fast_parse_options(struct sk_buff *skb, struct tcphdr *th, struct tcp_opt *tp) { if (th->doff == sizeof(struct tcphdr)>>2) { tp->saw_tstamp = 0; return 0; } else if (tp->tstamp_ok && th->doff == (sizeof(struct tcphdr)>>2)+(TCPOLEN_TSTAMP_ALIGNED>>2)) { __u32 *ptr = (__u32 *)(th + 1); if (*ptr == ntohl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) { tp->saw_tstamp = 1; ++ptr; tp->rcv_tsval = ntohl(*ptr); ++ptr; tp->rcv_tsecr = ntohl(*ptr); return 1; } } tcp_parse_options(skb, tp, 1); return 1; } static __inline__ void tcp_store_ts_recent(struct tcp_opt *tp) { tp->ts_recent = tp->rcv_tsval; tp->ts_recent_stamp = xtime.tv_sec; } static __inline__ void tcp_replace_ts_recent(struct tcp_opt *tp, u32 seq) { if (tp->saw_tstamp && !after(seq, tp->rcv_wup)) { /* PAWS bug workaround wrt. ACK frames, the PAWS discard * extra check below makes sure this can only happen * for pure ACK frames. -DaveM * * Not only, also it occurs for expired timestamps. */ if((s32)(tp->rcv_tsval - tp->ts_recent) >= 0 || xtime.tv_sec >= tp->ts_recent_stamp + TCP_PAWS_24DAYS) tcp_store_ts_recent(tp); } } /* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM * * It is not fatal. If this ACK does _not_ change critical state (seqs, window) * it can pass through stack. So, the following predicate verifies that * this segment is not used for anything but congestion avoidance or * fast retransmit. Moreover, we even are able to eliminate most of such * second order effects, if we apply some small "replay" window (~RTO) * to timestamp space. * * All these measures still do not guarantee that we reject wrapped ACKs * on networks with high bandwidth, when sequence space is recycled fastly, * but it guarantees that such events will be very rare and do not affect * connection seriously. This doesn't look nice, but alas, PAWS is really * buggy extension. * * [ Later note. Even worse! It is buggy for segments _with_ data. RFC * states that events when retransmit arrives after original data are rare. * It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is * the biggest problem on large power networks even with minor reordering. * OK, let's give it small replay window. If peer clock is even 1hz, it is safe * up to bandwidth of 18Gigabit/sec. 8) ] */ static int tcp_disordered_ack(struct tcp_opt *tp, struct sk_buff *skb) { struct tcphdr *th = skb->h.th; u32 seq = TCP_SKB_CB(skb)->seq; u32 ack = TCP_SKB_CB(skb)->ack_seq; return (/* 1. Pure ACK with correct sequence number. */ (th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) && /* 2. ... and duplicate ACK. */ ack == tp->snd_una && /* 3. ... and does not update window. */ !tcp_may_update_window(tp, ack, seq, ntohs(th->window)<<tp->snd_wscale) && /* 4. ... and sits in replay window. */ (s32)(tp->ts_recent - tp->rcv_tsval) <= (tp->rto*1024)/HZ); } static __inline__ int tcp_paws_discard(struct tcp_opt *tp, struct sk_buff *skb) { return ((s32)(tp->ts_recent - tp->rcv_tsval) > TCP_PAWS_WINDOW && xtime.tv_sec < tp->ts_recent_stamp + TCP_PAWS_24DAYS && !tcp_disordered_ack(tp, skb)); } /* Check segment sequence number for validity. * * Segment controls are considered valid, if the segment * fits to the window after truncation to the window. Acceptability * of data (and SYN, FIN, of course) is checked separately. * See tcp_data_queue(), for example. * * Also, controls (RST is main one) are accepted using RCV.WUP instead * of RCV.NXT. Peer still did not advance his SND.UNA when we * delayed ACK, so that hisSND.UNA<=ourRCV.WUP. * (borrowed from freebsd) */ static inline int tcp_sequence(struct tcp_opt *tp, u32 seq, u32 end_seq) { return !before(end_seq, tp->rcv_wup) && !after(seq, tp->rcv_nxt + tcp_receive_window(tp)); } /* When we get a reset we do this. */ static void tcp_reset(struct sock *sk) { /* We want the right error as BSD sees it (and indeed as we do). */ switch (sk->sk_state) { case TCP_SYN_SENT: sk->sk_err = ECONNREFUSED; break; case TCP_CLOSE_WAIT: sk->sk_err = EPIPE; break; case TCP_CLOSE: return; default: sk->sk_err = ECONNRESET; } if (!sock_flag(sk, SOCK_DEAD)) sk->sk_error_report(sk); tcp_done(sk); } /* * Process the FIN bit. This now behaves as it is supposed to work * and the FIN takes effect when it is validly part of sequence * space. Not before when we get holes. * * If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT * (and thence onto LAST-ACK and finally, CLOSE, we never enter * TIME-WAIT) * * If we are in FINWAIT-1, a received FIN indicates simultaneous * close and we go into CLOSING (and later onto TIME-WAIT) * * If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT. */ static void tcp_fin(struct sk_buff *skb, struct sock *sk, struct tcphdr *th) { struct tcp_opt *tp = tcp_sk(sk); tcp_schedule_ack(tp); sk->sk_shutdown |= RCV_SHUTDOWN; sock_reset_flag(sk, SOCK_DONE); switch (sk->sk_state) { case TCP_SYN_RECV: case TCP_ESTABLISHED: /* Move to CLOSE_WAIT */ tcp_set_state(sk, TCP_CLOSE_WAIT); tp->ack.pingpong = 1; break; case TCP_CLOSE_WAIT: case TCP_CLOSING: /* Received a retransmission of the FIN, do * nothing. */ break; case TCP_LAST_ACK: /* RFC793: Remain in the LAST-ACK state. */ break; case TCP_FIN_WAIT1: /* This case occurs when a simultaneous close * happens, we must ack the received FIN and * enter the CLOSING state. */ tcp_send_ack(sk); tcp_set_state(sk, TCP_CLOSING); break; case TCP_FIN_WAIT2: /* Received a FIN -- send ACK and enter TIME_WAIT. */ tcp_send_ack(sk); tcp_time_wait(sk, TCP_TIME_WAIT, 0); break; default: /* Only TCP_LISTEN and TCP_CLOSE are left, in these * cases we should never reach this piece of code. */ printk(KERN_ERR "%s: Impossible, sk->sk_state=%d\n", __FUNCTION__, sk->sk_state); break; }; /* It _is_ possible, that we have something out-of-order _after_ FIN. * Probably, we should reset in this case. For now drop them. */ __skb_queue_purge(&tp->out_of_order_queue); if (tp->sack_ok) tcp_sack_reset(tp); tcp_mem_reclaim(sk); if (!sock_flag(sk, SOCK_DEAD)) { sk->sk_state_change(sk); /* Do not send POLL_HUP for half duplex close. */ if (sk->sk_shutdown == SHUTDOWN_MASK || sk->sk_state == TCP_CLOSE) sk_wake_async(sk, 1, POLL_HUP); else sk_wake_async(sk, 1, POLL_IN); } } static __inline__ int tcp_sack_extend(struct tcp_sack_block *sp, u32 seq, u32 end_seq) { if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) { if (before(seq, sp->start_seq)) sp->start_seq = seq; if (after(end_seq, sp->end_seq)) sp->end_seq = end_seq; return 1; } return 0; } static __inline__ void tcp_dsack_set(struct tcp_opt *tp, u32 seq, u32 end_seq) { if (tp->sack_ok && sysctl_tcp_dsack) { if (before(seq, tp->rcv_nxt)) NET_INC_STATS_BH(TCPDSACKOldSent); else NET_INC_STATS_BH(TCPDSACKOfoSent); tp->dsack = 1; tp->duplicate_sack[0].start_seq = seq; tp->duplicate_sack[0].end_seq = end_seq; tp->eff_sacks = min(tp->num_sacks+1, 4-tp->tstamp_ok); } } static __inline__ void tcp_dsack_extend(struct tcp_opt *tp, u32 seq, u32 end_seq) { if (!tp->dsack) tcp_dsack_set(tp, seq, end_seq); else tcp_sack_extend(tp->duplicate_sack, seq, end_seq); } static void tcp_send_dupack(struct sock *sk, struct sk_buff *skb) { struct tcp_opt *tp = tcp_sk(sk); if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq && before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) { NET_INC_STATS_BH(DelayedACKLost); tcp_enter_quickack_mode(tp); if (tp->sack_ok && sysctl_tcp_dsack) { u32 end_seq = TCP_SKB_CB(skb)->end_seq; if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) end_seq = tp->rcv_nxt; tcp_dsack_set(tp, TCP_SKB_CB(skb)->seq, end_seq); } } tcp_send_ack(sk); } /* These routines update the SACK block as out-of-order packets arrive or * in-order packets close up the sequence space. */ static void tcp_sack_maybe_coalesce(struct tcp_opt *tp) { int this_sack; struct tcp_sack_block *sp = &tp->selective_acks[0]; struct tcp_sack_block *swalk = sp+1; /* See if the recent change to the first SACK eats into * or hits the sequence space of other SACK blocks, if so coalesce. */ for (this_sack = 1; this_sack < tp->num_sacks; ) { if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) { int i; /* Zap SWALK, by moving every further SACK up by one slot. * Decrease num_sacks. */ tp->num_sacks--; tp->eff_sacks = min(tp->num_sacks+tp->dsack, 4-tp->tstamp_ok); for(i=this_sack; i < tp->num_sacks; i++) sp[i] = sp[i+1]; continue; } this_sack++, swalk++; } } static __inline__ void tcp_sack_swap(struct tcp_sack_block *sack1, struct tcp_sack_block *sack2) { __u32 tmp; tmp = sack1->start_seq; sack1->start_seq = sack2->start_seq; sack2->start_seq = tmp; tmp = sack1->end_seq; sack1->end_seq = sack2->end_seq; sack2->end_seq = tmp; } static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq) { struct tcp_opt *tp = tcp_sk(sk); struct tcp_sack_block *sp = &tp->selective_acks[0]; int cur_sacks = tp->num_sacks; int this_sack; if (!cur_sacks) goto new_sack; for (this_sack=0; this_sack<cur_sacks; this_sack++, sp++) { if (tcp_sack_extend(sp, seq, end_seq)) { /* Rotate this_sack to the first one. */ for (; this_sack>0; this_sack--, sp--) tcp_sack_swap(sp, sp-1); if (cur_sacks > 1) tcp_sack_maybe_coalesce(tp); return; } } /* Could not find an adjacent existing SACK, build a new one, * put it at the front, and shift everyone else down. We * always know there is at least one SACK present already here. * * If the sack array is full, forget about the last one. */ if (this_sack >= 4) { this_sack--; tp->num_sacks--; sp--; } for(; this_sack > 0; this_sack--, sp--) *sp = *(sp-1); new_sack: /* Build the new head SACK, and we're done. */ sp->start_seq = seq; sp->end_seq = end_seq; tp->num_sacks++; tp->eff_sacks = min(tp->num_sacks + tp->dsack, 4 - tp->tstamp_ok); } /* RCV.NXT advances, some SACKs should be eaten. */ static void tcp_sack_remove(struct tcp_opt *tp) { struct tcp_sack_block *sp = &tp->selective_acks[0]; int num_sacks = tp->num_sacks; int this_sack; /* Empty ofo queue, hence, all the SACKs are eaten. Clear. */ if (skb_queue_len(&tp->out_of_order_queue) == 0) { tp->num_sacks = 0; tp->eff_sacks = tp->dsack; return; } for(this_sack = 0; this_sack < num_sacks; ) { /* Check if the start of the sack is covered by RCV.NXT. */ if (!before(tp->rcv_nxt, sp->start_seq)) { int i; /* RCV.NXT must cover all the block! */ BUG_TRAP(!before(tp->rcv_nxt, sp->end_seq)); /* Zap this SACK, by moving forward any other SACKS. */ for (i=this_sack+1; i < num_sacks; i++) tp->selective_acks[i-1] = tp->selective_acks[i]; num_sacks--; continue; } this_sack++; sp++; } if (num_sacks != tp->num_sacks) { tp->num_sacks = num_sacks; tp->eff_sacks = min(tp->num_sacks+tp->dsack, 4-tp->tstamp_ok); } } /* This one checks to see if we can put data from the * out_of_order queue into the receive_queue. */ static void tcp_ofo_queue(struct sock *sk) { struct tcp_opt *tp = tcp_sk(sk); __u32 dsack_high = tp->rcv_nxt; struct sk_buff *skb; while ((skb = skb_peek(&tp->out_of_order_queue)) != NULL) { if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) break; if (before(TCP_SKB_CB(skb)->seq, dsack_high)) { __u32 dsack = dsack_high; if (before(TCP_SKB_CB(skb)->end_seq, dsack_high)) dsack_high = TCP_SKB_CB(skb)->end_seq; tcp_dsack_extend(tp, TCP_SKB_CB(skb)->seq, dsack); } if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) { SOCK_DEBUG(sk, "ofo packet was already received \n"); __skb_unlink(skb, skb->list); __kfree_skb(skb); continue; } SOCK_DEBUG(sk, "ofo requeuing : rcv_next %X seq %X - %X\n", tp->rcv_nxt, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq); __skb_unlink(skb, skb->list); __skb_queue_tail(&sk->sk_receive_queue, skb); tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq; if(skb->h.th->fin) tcp_fin(skb, sk, skb->h.th); } } static inline int tcp_rmem_schedule(struct sock *sk, struct sk_buff *skb) { return (int)skb->truesize <= sk->sk_forward_alloc || tcp_mem_schedule(sk, skb->truesize, 1); } static int tcp_prune_queue(struct sock *sk); static void tcp_data_queue(struct sock *sk, struct sk_buff *skb) { struct tcphdr *th = skb->h.th; struct tcp_opt *tp = tcp_sk(sk); int eaten = -1; if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq) goto drop; th = skb->h.th; __skb_pull(skb, th->doff*4); TCP_ECN_accept_cwr(tp, skb); if (tp->dsack) { tp->dsack = 0; tp->eff_sacks = min_t(unsigned int, tp->num_sacks, 4 - tp->tstamp_ok); } /* Queue data for delivery to the user. * Packets in sequence go to the receive queue. * Out of sequence packets to the out_of_order_queue. */ if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) { if (tcp_receive_window(tp) == 0) goto out_of_window; /* Ok. In sequence. In window. */ if (tp->ucopy.task == current && tp->copied_seq == tp->rcv_nxt && tp->ucopy.len && sock_owned_by_user(sk) && !tp->urg_data) { int chunk = min_t(unsigned int, skb->len, tp->ucopy.len); __set_current_state(TASK_RUNNING); local_bh_enable(); if (!skb_copy_datagram_iovec(skb, 0, tp->ucopy.iov, chunk)) { tp->ucopy.len -= chunk; tp->copied_seq += chunk; eaten = (chunk == skb->len && !th->fin); } local_bh_disable(); } if (eaten <= 0) { queue_and_out: if (eaten < 0 && (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf || !tcp_rmem_schedule(sk, skb))) { if (tcp_prune_queue(sk) < 0 || !tcp_rmem_schedule(sk, skb)) goto drop; } tcp_set_owner_r(skb, sk); __skb_queue_tail(&sk->sk_receive_queue, skb); } tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq; if(skb->len) tcp_event_data_recv(sk, tp, skb); if(th->fin) tcp_fin(skb, sk, th); if (skb_queue_len(&tp->out_of_order_queue)) { tcp_ofo_queue(sk); /* RFC2581. 4.2. SHOULD send immediate ACK, when * gap in queue is filled. */ if (!skb_queue_len(&tp->out_of_order_queue)) tp->ack.pingpong = 0; } if (tp->num_sacks) tcp_sack_remove(tp); tcp_fast_path_check(sk, tp); if (eaten > 0) __kfree_skb(skb); else if (!sock_flag(sk, SOCK_DEAD)) sk->sk_data_ready(sk, 0); return; } if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) { /* A retransmit, 2nd most common case. Force an immediate ack. */ NET_INC_STATS_BH(DelayedACKLost); tcp_dsack_set(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq); out_of_window: tcp_enter_quickack_mode(tp); tcp_schedule_ack(tp); drop: __kfree_skb(skb); return; } /* Out of window. F.e. zero window probe. */ if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt + tcp_receive_window(tp))) goto out_of_window; tcp_enter_quickack_mode(tp); if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) { /* Partial packet, seq < rcv_next < end_seq */ SOCK_DEBUG(sk, "partial packet: rcv_next %X seq %X - %X\n", tp->rcv_nxt, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq); tcp_dsack_set(tp, TCP_SKB_CB(skb)->seq, tp->rcv_nxt); /* If window is closed, drop tail of packet. But after * remembering D-SACK for its head made in previous line. */ if (!tcp_receive_window(tp)) goto out_of_window; goto queue_and_out; } TCP_ECN_check_ce(tp, skb); if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf || !tcp_rmem_schedule(sk, skb)) { if (tcp_prune_queue(sk) < 0 || !tcp_rmem_schedule(sk, skb)) goto drop; } /* Disable header prediction. */ tp->pred_flags = 0; tcp_schedule_ack(tp); SOCK_DEBUG(sk, "out of order segment: rcv_next %X seq %X - %X\n", tp->rcv_nxt, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq); tcp_set_owner_r(skb, sk); if (!skb_peek(&tp->out_of_order_queue)) { /* Initial out of order segment, build 1 SACK. */ if (tp->sack_ok) { tp->num_sacks = 1; tp->dsack = 0; tp->eff_sacks = 1; tp->selective_acks[0].start_seq = TCP_SKB_CB(skb)->seq; tp->selective_acks[0].end_seq = TCP_SKB_CB(skb)->end_seq; } __skb_queue_head(&tp->out_of_order_queue,skb); } else { struct sk_buff *skb1 = tp->out_of_order_queue.prev; u32 seq = TCP_SKB_CB(skb)->seq; u32 end_seq = TCP_SKB_CB(skb)->end_seq; if (seq == TCP_SKB_CB(skb1)->end_seq) { __skb_append(skb1, skb); if (!tp->num_sacks || tp->selective_acks[0].end_seq != seq) goto add_sack; /* Common case: data arrive in order after hole. */ tp->selective_acks[0].end_seq = end_seq; return; } /* Find place to insert this segment. */ do { if (!after(TCP_SKB_CB(skb1)->seq, seq)) break; } while ((skb1 = skb1->prev) != (struct sk_buff*)&tp->out_of_order_queue); /* Do skb overlap to previous one? */ if (skb1 != (struct sk_buff*)&tp->out_of_order_queue && before(seq, TCP_SKB_CB(skb1)->end_seq)) { if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) { /* All the bits are present. Drop. */ __kfree_skb(skb); tcp_dsack_set(tp, seq, end_seq); goto add_sack; } if (after(seq, TCP_SKB_CB(skb1)->seq)) { /* Partial overlap. */ tcp_dsack_set(tp, seq, TCP_SKB_CB(skb1)->end_seq); } else { skb1 = skb1->prev; } } __skb_insert(skb, skb1, skb1->next, &tp->out_of_order_queue); /* And clean segments covered by new one as whole. */ while ((skb1 = skb->next) != (struct sk_buff*)&tp->out_of_order_queue && after(end_seq, TCP_SKB_CB(skb1)->seq)) { if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) { tcp_dsack_extend(tp, TCP_SKB_CB(skb1)->seq, end_seq); break; } __skb_unlink(skb1, skb1->list); tcp_dsack_extend(tp, TCP_SKB_CB(skb1)->seq, TCP_SKB_CB(skb1)->end_seq); __kfree_skb(skb1); } add_sack: if (tp->sack_ok) tcp_sack_new_ofo_skb(sk, seq, end_seq); } } /* Collapse contiguous sequence of skbs head..tail with * sequence numbers start..end. * Segments with FIN/SYN are not collapsed (only because this * simplifies code) */ static void tcp_collapse(struct sock *sk, struct sk_buff *head, struct sk_buff *tail, u32 start, u32 end) { struct sk_buff *skb; /* First, check that queue is collapsable and find * the point where collapsing can be useful. */ for (skb = head; skb != tail; ) { /* No new bits? It is possible on ofo queue. */ if (!before(start, TCP_SKB_CB(skb)->end_seq)) { struct sk_buff *next = skb->next; __skb_unlink(skb, skb->list); __kfree_skb(skb); NET_INC_STATS_BH(TCPRcvCollapsed); skb = next; continue; } /* The first skb to collapse is: * - not SYN/FIN and * - bloated or contains data before "start" or * overlaps to the next one. */ if (!skb->h.th->syn && !skb->h.th->fin && (tcp_win_from_space(skb->truesize) > skb->len || before(TCP_SKB_CB(skb)->seq, start) || (skb->next != tail && TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb->next)->seq))) break; /* Decided to skip this, advance start seq. */ start = TCP_SKB_CB(skb)->end_seq; skb = skb->next; } if (skb == tail || skb->h.th->syn || skb->h.th->fin) return; while (before(start, end)) { struct sk_buff *nskb; int header = skb_headroom(skb); int copy = (PAGE_SIZE - sizeof(struct sk_buff) - sizeof(struct skb_shared_info) - header - 31)&~15; /* Too big header? This can happen with IPv6. */ if (copy < 0) return; if (end-start < copy) copy = end-start; nskb = alloc_skb(copy+header, GFP_ATOMIC); if (!nskb) return; skb_reserve(nskb, header); memcpy(nskb->head, skb->head, header); nskb->nh.raw = nskb->head + (skb->nh.raw-skb->head); nskb->h.raw = nskb->head + (skb->h.raw-skb->head); nskb->mac.raw = nskb->head + (skb->mac.raw-skb->head); memcpy(nskb->cb, skb->cb, sizeof(skb->cb)); TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start; __skb_insert(nskb, skb->prev, skb, skb->list); tcp_set_owner_r(nskb, sk); /* Copy data, releasing collapsed skbs. */ while (copy > 0) { int offset = start - TCP_SKB_CB(skb)->seq; int size = TCP_SKB_CB(skb)->end_seq - start; if (offset < 0) BUG(); if (size > 0) { size = min(copy, size); if (skb_copy_bits(skb, offset, skb_put(nskb, size), size)) BUG(); TCP_SKB_CB(nskb)->end_seq += size; copy -= size; start += size; } if (!before(start, TCP_SKB_CB(skb)->end_seq)) { struct sk_buff *next = skb->next; __skb_unlink(skb, skb->list); __kfree_skb(skb); NET_INC_STATS_BH(TCPRcvCollapsed); skb = next; if (skb == tail || skb->h.th->syn || skb->h.th->fin) return; } } } } /* Collapse ofo queue. Algorithm: select contiguous sequence of skbs * and tcp_collapse() them until all the queue is collapsed. */ static void tcp_collapse_ofo_queue(struct sock *sk) { struct tcp_opt *tp = tcp_sk(sk); struct sk_buff *skb = skb_peek(&tp->out_of_order_queue); struct sk_buff *head; u32 start, end; if (skb == NULL) return; start = TCP_SKB_CB(skb)->seq; end = TCP_SKB_CB(skb)->end_seq; head = skb; for (;;) { skb = skb->next; /* Segment is terminated when we see gap or when * we are at the end of all the queue. */ if (skb == (struct sk_buff *)&tp->out_of_order_queue || after(TCP_SKB_CB(skb)->seq, end) || before(TCP_SKB_CB(skb)->end_seq, start)) { tcp_collapse(sk, head, skb, start, end); head = skb; if (skb == (struct sk_buff *)&tp->out_of_order_queue) break; /* Start new segment */ start = TCP_SKB_CB(skb)->seq; end = TCP_SKB_CB(skb)->end_seq; } else { if (before(TCP_SKB_CB(skb)->seq, start)) start = TCP_SKB_CB(skb)->seq; if (after(TCP_SKB_CB(skb)->end_seq, end)) end = TCP_SKB_CB(skb)->end_seq; } } } /* Reduce allocated memory if we can, trying to get * the socket within its memory limits again. * * Return less than zero if we should start dropping frames * until the socket owning process reads some of the data * to stabilize the situation. */ static int tcp_prune_queue(struct sock *sk) { struct tcp_opt *tp = tcp_sk(sk); SOCK_DEBUG(sk, "prune_queue: c=%x\n", tp->copied_seq); NET_INC_STATS_BH(PruneCalled); if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf) tcp_clamp_window(sk, tp); else if (tcp_memory_pressure) tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U * tp->advmss); tcp_collapse_ofo_queue(sk); tcp_collapse(sk, sk->sk_receive_queue.next, (struct sk_buff*)&sk->sk_receive_queue, tp->copied_seq, tp->rcv_nxt); tcp_mem_reclaim(sk); if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf) return 0; /* Collapsing did not help, destructive actions follow. * This must not ever occur. */ /* First, purge the out_of_order queue. */ if (skb_queue_len(&tp->out_of_order_queue)) { NET_ADD_STATS_BH(OfoPruned, skb_queue_len(&tp->out_of_order_queue)); __skb_queue_purge(&tp->out_of_order_queue); /* Reset SACK state. A conforming SACK implementation will * do the same at a timeout based retransmit. When a connection * is in a sad state like this, we care only about integrity * of the connection not performance. */ if (tp->sack_ok) tcp_sack_reset(tp); tcp_mem_reclaim(sk); } if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf) return 0; /* If we are really being abused, tell the caller to silently * drop receive data on the floor. It will get retransmitted * and hopefully then we'll have sufficient space. */ NET_INC_STATS_BH(RcvPruned); /* Massive buffer overcommit. */ tp->pred_flags = 0; return -1; } /* RFC2861, slow part. Adjust cwnd, after it was not full during one rto. * As additional protections, we do not touch cwnd in retransmission phases, * and if application hit its sndbuf limit recently. */ void tcp_cwnd_application_limited(struct sock *sk) { struct tcp_opt *tp = tcp_sk(sk); if (tp->ca_state == TCP_CA_Open && sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) { /* Limited by application or receiver window. */ u32 win_used = max(tp->snd_cwnd_used, 2U); if (win_used < tp->snd_cwnd) { tp->snd_ssthresh = tcp_current_ssthresh(tp); tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1; } tp->snd_cwnd_used = 0; } tp->snd_cwnd_stamp = tcp_time_stamp; } /* When incoming ACK allowed to free some skb from write_queue, * we remember this event in flag tp->queue_shrunk and wake up socket * on the exit from tcp input handler. * * PROBLEM: sndbuf expansion does not work well with largesend. */ static void tcp_new_space(struct sock *sk) { struct tcp_opt *tp = tcp_sk(sk); if (tp->packets_out < tp->snd_cwnd && !(sk->sk_userlocks & SOCK_SNDBUF_LOCK) && !tcp_memory_pressure && atomic_read(&tcp_memory_allocated) < sysctl_tcp_mem[0]) { int sndmem = max_t(u32, tp->mss_clamp, tp->mss_cache) + MAX_TCP_HEADER + 16 + sizeof(struct sk_buff), demanded = max_t(unsigned int, tp->snd_cwnd, tp->reordering + 1); sndmem *= 2*demanded; if (sndmem > sk->sk_sndbuf) sk->sk_sndbuf = min(sndmem, sysctl_tcp_wmem[2]); tp->snd_cwnd_stamp = tcp_time_stamp; } sk->sk_write_space(sk); } static inline void tcp_check_space(struct sock *sk) { struct tcp_opt *tp = tcp_sk(sk); if (tp->queue_shrunk) { tp->queue_shrunk = 0; if (sk->sk_socket && test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) tcp_new_space(sk); } } static void __tcp_data_snd_check(struct sock *sk, struct sk_buff *skb) { struct tcp_opt *tp = tcp_sk(sk); if (after(TCP_SKB_CB(skb)->end_seq, tp->snd_una + tp->snd_wnd) || tcp_packets_in_flight(tp) >= tp->snd_cwnd || tcp_write_xmit(sk, tp->nonagle)) tcp_check_probe_timer(sk, tp); } static __inline__ void tcp_data_snd_check(struct sock *sk) { struct tcp_opt *tp = tcp_sk(sk); struct sk_buff *skb = tp->send_head; if (skb != NULL) __tcp_data_snd_check(sk, skb); tcp_check_space(sk); } /* * Check if sending an ack is needed. */ static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible) { struct tcp_opt *tp = tcp_sk(sk); /* More than one full frame received... */ if (((tp->rcv_nxt - tp->rcv_wup) > tp->ack.rcv_mss /* ... and right edge of window advances far enough. * (tcp_recvmsg() will send ACK otherwise). Or... */ && __tcp_select_window(sk) >= tp->rcv_wnd) || /* We ACK each frame or... */ tcp_in_quickack_mode(tp) || /* We have out of order data. */ (ofo_possible && skb_peek(&tp->out_of_order_queue))) { /* Then ack it now */ tcp_send_ack(sk); } else { /* Else, send delayed ack. */ tcp_send_delayed_ack(sk); } } static __inline__ void tcp_ack_snd_check(struct sock *sk) { struct tcp_opt *tp = tcp_sk(sk); if (!tcp_ack_scheduled(tp)) { /* We sent a data segment already. */ return; } __tcp_ack_snd_check(sk, 1); } /* * This routine is only called when we have urgent data * signalled. Its the 'slow' part of tcp_urg. It could be * moved inline now as tcp_urg is only called from one * place. We handle URGent data wrong. We have to - as * BSD still doesn't use the correction from RFC961. * For 1003.1g we should support a new option TCP_STDURG to permit * either form (or just set the sysctl tcp_stdurg). */ static void tcp_check_urg(struct sock * sk, struct tcphdr * th) { struct tcp_opt *tp = tcp_sk(sk); u32 ptr = ntohs(th->urg_ptr); if (ptr && !sysctl_tcp_stdurg) ptr--; ptr += ntohl(th->seq); /* Ignore urgent data that we've already seen and read. */ if (after(tp->copied_seq, ptr)) return; /* Do not replay urg ptr. * * NOTE: interesting situation not covered by specs. * Misbehaving sender may send urg ptr, pointing to segment, * which we already have in ofo queue. We are not able to fetch * such data and will stay in TCP_URG_NOTYET until will be eaten * by recvmsg(). Seems, we are not obliged to handle such wicked * situations. But it is worth to think about possibility of some * DoSes using some hypothetical application level deadlock. */ if (before(ptr, tp->rcv_nxt)) return; /* Do we already have a newer (or duplicate) urgent pointer? */ if (tp->urg_data && !after(ptr, tp->urg_seq)) return; /* Tell the world about our new urgent pointer. */ sk_send_sigurg(sk); /* We may be adding urgent data when the last byte read was * urgent. To do this requires some care. We cannot just ignore * tp->copied_seq since we would read the last urgent byte again * as data, nor can we alter copied_seq until this data arrives * or we break the sematics of SIOCATMARK (and thus sockatmark()) * * NOTE. Double Dutch. Rendering to plain English: author of comment * above did something sort of send("A", MSG_OOB); send("B", MSG_OOB); * and expect that both A and B disappear from stream. This is _wrong_. * Though this happens in BSD with high probability, this is occasional. * Any application relying on this is buggy. Note also, that fix "works" * only in this artificial test. Insert some normal data between A and B and we will * decline of BSD again. Verdict: it is better to remove to trap * buggy users. */ if (tp->urg_seq == tp->copied_seq && tp->urg_data && !sock_flag(sk, SOCK_URGINLINE) && tp->copied_seq != tp->rcv_nxt) { struct sk_buff *skb = skb_peek(&sk->sk_receive_queue); tp->copied_seq++; if (skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq)) { __skb_unlink(skb, skb->list); __kfree_skb(skb); } } tp->urg_data = TCP_URG_NOTYET; tp->urg_seq = ptr; /* Disable header prediction. */ tp->pred_flags = 0; } /* This is the 'fast' part of urgent handling. */ static void tcp_urg(struct sock *sk, struct sk_buff *skb, struct tcphdr *th) { struct tcp_opt *tp = tcp_sk(sk); /* Check if we get a new urgent pointer - normally not. */ if (th->urg) tcp_check_urg(sk,th); /* Do we wait for any urgent data? - normally not... */ if (tp->urg_data == TCP_URG_NOTYET) { u32 ptr = tp->urg_seq - ntohl(th->seq) + (th->doff * 4) - th->syn; /* Is the urgent pointer pointing into this packet? */ if (ptr < skb->len) { u8 tmp; if (skb_copy_bits(skb, ptr, &tmp, 1)) BUG(); tp->urg_data = TCP_URG_VALID | tmp; if (!sock_flag(sk, SOCK_DEAD)) sk->sk_data_ready(sk, 0); } } } static int tcp_copy_to_iovec(struct sock *sk, struct sk_buff *skb, int hlen) { struct tcp_opt *tp = tcp_sk(sk); int chunk = skb->len - hlen; int err; local_bh_enable(); if (skb->ip_summed==CHECKSUM_UNNECESSARY) err = skb_copy_datagram_iovec(skb, hlen, tp->ucopy.iov, chunk); else err = skb_copy_and_csum_datagram_iovec(skb, hlen, tp->ucopy.iov); if (!err) { tp->ucopy.len -= chunk; tp->copied_seq += chunk; } local_bh_disable(); return err; } static int __tcp_checksum_complete_user(struct sock *sk, struct sk_buff *skb) { int result; if (sock_owned_by_user(sk)) { local_bh_enable(); result = __tcp_checksum_complete(skb); local_bh_disable(); } else { result = __tcp_checksum_complete(skb); } return result; } static __inline__ int tcp_checksum_complete_user(struct sock *sk, struct sk_buff *skb) { return skb->ip_summed != CHECKSUM_UNNECESSARY && __tcp_checksum_complete_user(sk, skb); } /* * TCP receive function for the ESTABLISHED state. * * It is split into a fast path and a slow path. The fast path is * disabled when: * - A zero window was announced from us - zero window probing * is only handled properly in the slow path. * - Out of order segments arrived. * - Urgent data is expected. * - There is no buffer space left * - Unexpected TCP flags/window values/header lengths are received * (detected by checking the TCP header against pred_flags) * - Data is sent in both directions. Fast path only supports pure senders * or pure receivers (this means either the sequence number or the ack * value must stay constant) * - Unexpected TCP option. * * When these conditions are not satisfied it drops into a standard * receive procedure patterned after RFC793 to handle all cases. * The first three cases are guaranteed by proper pred_flags setting, * the rest is checked inline. Fast processing is turned on in * tcp_data_queue when everything is OK. */ int tcp_rcv_established(struct sock *sk, struct sk_buff *skb, struct tcphdr *th, unsigned len) { struct tcp_opt *tp = tcp_sk(sk); /* * Header prediction. * The code loosely follows the one in the famous * "30 instruction TCP receive" Van Jacobson mail. * * Van's trick is to deposit buffers into socket queue * on a device interrupt, to call tcp_recv function * on the receive process context and checksum and copy * the buffer to user space. smart... * * Our current scheme is not silly either but we take the * extra cost of the net_bh soft interrupt processing... * We do checksum and copy also but from device to kernel. */ tp->saw_tstamp = 0; /* pred_flags is 0xS?10 << 16 + snd_wnd * if header_predition is to be made * 'S' will always be tp->tcp_header_len >> 2 * '?' will be 0 for the fast path, otherwise pred_flags is 0 to * turn it off (when there are holes in the receive * space for instance) * PSH flag is ignored. */ if ((tcp_flag_word(th) & TCP_HP_BITS) == tp->pred_flags && TCP_SKB_CB(skb)->seq == tp->rcv_nxt) { int tcp_header_len = tp->tcp_header_len; /* Timestamp header prediction: tcp_header_len * is automatically equal to th->doff*4 due to pred_flags * match. */ /* Check timestamp */ if (tcp_header_len == sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) { __u32 *ptr = (__u32 *)(th + 1); /* No? Slow path! */ if (*ptr != ntohl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) goto slow_path; tp->saw_tstamp = 1; ++ptr; tp->rcv_tsval = ntohl(*ptr); ++ptr; tp->rcv_tsecr = ntohl(*ptr); /* If PAWS failed, check it more carefully in slow path */ if ((s32)(tp->rcv_tsval - tp->ts_recent) < 0) goto slow_path; /* DO NOT update ts_recent here, if checksum fails * and timestamp was corrupted part, it will result * in a hung connection since we will drop all * future packets due to the PAWS test. */ } if (len <= tcp_header_len) { /* Bulk data transfer: sender */ if (len == tcp_header_len) { /* Predicted packet is in window by definition. * seq == rcv_nxt and rcv_wup <= rcv_nxt. * Hence, check seq<=rcv_wup reduces to: */ if (tcp_header_len == (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) && tp->rcv_nxt == tp->rcv_wup) tcp_store_ts_recent(tp); /* We know that such packets are checksummed * on entry. */ tcp_ack(sk, skb, 0); __kfree_skb(skb); tcp_data_snd_check(sk); return 0; } else { /* Header too small */ TCP_INC_STATS_BH(TcpInErrs); goto discard; } } else { int eaten = 0; if (tp->ucopy.task == current && tp->copied_seq == tp->rcv_nxt && len - tcp_header_len <= tp->ucopy.len && sock_owned_by_user(sk)) { __set_current_state(TASK_RUNNING); if (!tcp_copy_to_iovec(sk, skb, tcp_header_len)) { /* Predicted packet is in window by definition. * seq == rcv_nxt and rcv_wup <= rcv_nxt. * Hence, check seq<=rcv_wup reduces to: */ if (tcp_header_len == (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) && tp->rcv_nxt == tp->rcv_wup) tcp_store_ts_recent(tp); __skb_pull(skb, tcp_header_len); tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq; NET_INC_STATS_BH(TCPHPHitsToUser); eaten = 1; } } if (!eaten) { if (tcp_checksum_complete_user(sk, skb)) goto csum_error; /* Predicted packet is in window by definition. * seq == rcv_nxt and rcv_wup <= rcv_nxt. * Hence, check seq<=rcv_wup reduces to: */ if (tcp_header_len == (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) && tp->rcv_nxt == tp->rcv_wup) tcp_store_ts_recent(tp); if ((int)skb->truesize > sk->sk_forward_alloc) goto step5; NET_INC_STATS_BH(TCPHPHits); /* Bulk data transfer: receiver */ __skb_pull(skb,tcp_header_len); __skb_queue_tail(&sk->sk_receive_queue, skb); tcp_set_owner_r(skb, sk); tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq; } tcp_event_data_recv(sk, tp, skb); if (TCP_SKB_CB(skb)->ack_seq != tp->snd_una) { /* Well, only one small jumplet in fast path... */ tcp_ack(sk, skb, FLAG_DATA); tcp_data_snd_check(sk); if (!tcp_ack_scheduled(tp)) goto no_ack; } if (eaten) { if (tcp_in_quickack_mode(tp)) { tcp_send_ack(sk); } else { tcp_send_delayed_ack(sk); } } else { __tcp_ack_snd_check(sk, 0); } no_ack: if (eaten) __kfree_skb(skb); else sk->sk_data_ready(sk, 0); return 0; } } slow_path: if (len < (th->doff<<2) || tcp_checksum_complete_user(sk, skb)) goto csum_error; /* * RFC1323: H1. Apply PAWS check first. */ if (tcp_fast_parse_options(skb, th, tp) && tp->saw_tstamp && tcp_paws_discard(tp, skb)) { if (!th->rst) { NET_INC_STATS_BH(PAWSEstabRejected); tcp_send_dupack(sk, skb); goto discard; } /* Resets are accepted even if PAWS failed. ts_recent update must be made after we are sure that the packet is in window. */ } /* * Standard slow path. */ if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) { /* RFC793, page 37: "In all states except SYN-SENT, all reset * (RST) segments are validated by checking their SEQ-fields." * And page 69: "If an incoming segment is not acceptable, * an acknowledgment should be sent in reply (unless the RST bit * is set, if so drop the segment and return)". */ if (!th->rst) tcp_send_dupack(sk, skb); goto discard; } if(th->rst) { tcp_reset(sk); goto discard; } tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq); if (th->syn && !before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) { TCP_INC_STATS_BH(TcpInErrs); NET_INC_STATS_BH(TCPAbortOnSyn); tcp_reset(sk); return 1; } step5: if(th->ack) tcp_ack(sk, skb, FLAG_SLOWPATH); /* Process urgent data. */ tcp_urg(sk, skb, th); /* step 7: process the segment text */ tcp_data_queue(sk, skb); tcp_data_snd_check(sk); tcp_ack_snd_check(sk); return 0; csum_error: TCP_INC_STATS_BH(TcpInErrs); discard: __kfree_skb(skb); return 0; } static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb, struct tcphdr *th, unsigned len) { struct tcp_opt *tp = tcp_sk(sk); int saved_clamp = tp->mss_clamp; tcp_parse_options(skb, tp, 0); if (th->ack) { /* rfc793: * "If the state is SYN-SENT then * first check the ACK bit * If the ACK bit is set * If SEG.ACK =< ISS, or SEG.ACK > SND.NXT, send * a reset (unless the RST bit is set, if so drop * the segment and return)" * * We do not send data with SYN, so that RFC-correct * test reduces to: */ if (TCP_SKB_CB(skb)->ack_seq != tp->snd_nxt) goto reset_and_undo; if (tp->saw_tstamp && tp->rcv_tsecr && !between(tp->rcv_tsecr, tp->retrans_stamp, tcp_time_stamp)) { NET_INC_STATS_BH(PAWSActiveRejected); goto reset_and_undo; } /* Now ACK is acceptable. * * "If the RST bit is set * If the ACK was acceptable then signal the user "error: * connection reset", drop the segment, enter CLOSED state, * delete TCB, and return." */ if (th->rst) { tcp_reset(sk); goto discard; } /* rfc793: * "fifth, if neither of the SYN or RST bits is set then * drop the segment and return." * * See note below! * --ANK(990513) */ if (!th->syn) goto discard_and_undo; /* rfc793: * "If the SYN bit is on ... * are acceptable then ... * (our SYN has been ACKed), change the connection * state to ESTABLISHED..." */ TCP_ECN_rcv_synack(tp, th); if (tp->ecn_flags&TCP_ECN_OK) sk->sk_no_largesend = 1; tp->snd_wl1 = TCP_SKB_CB(skb)->seq; tcp_ack(sk, skb, FLAG_SLOWPATH); /* Ok.. it's good. Set up sequence numbers and * move to established. */ tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1; tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1; /* RFC1323: The window in SYN & SYN/ACK segments is * never scaled. */ tp->snd_wnd = ntohs(th->window); tcp_init_wl(tp, TCP_SKB_CB(skb)->ack_seq, TCP_SKB_CB(skb)->seq); if (!tp->wscale_ok) { tp->snd_wscale = tp->rcv_wscale = 0; tp->window_clamp = min(tp->window_clamp, 65535U); } if (tp->saw_tstamp) { tp->tstamp_ok = 1; tp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED; tp->advmss -= TCPOLEN_TSTAMP_ALIGNED; tcp_store_ts_recent(tp); } else { tp->tcp_header_len = sizeof(struct tcphdr); } if (tp->sack_ok && sysctl_tcp_fack) tp->sack_ok |= 2; tcp_sync_mss(sk, tp->pmtu_cookie); tcp_initialize_rcv_mss(sk); tcp_init_metrics(sk); tcp_init_buffer_space(sk); if (sock_flag(sk, SOCK_KEEPOPEN)) tcp_reset_keepalive_timer(sk, keepalive_time_when(tp)); if (!tp->snd_wscale) __tcp_fast_path_on(tp, tp->snd_wnd); else tp->pred_flags = 0; /* Remember, tcp_poll() does not lock socket! * Change state from SYN-SENT only after copied_seq * is initialized. */ tp->copied_seq = tp->rcv_nxt; mb(); tcp_set_state(sk, TCP_ESTABLISHED); if (!sock_flag(sk, SOCK_DEAD)) { sk->sk_state_change(sk); sk_wake_async(sk, 0, POLL_OUT); } if (tp->write_pending || tp->defer_accept || tp->ack.pingpong) { /* Save one ACK. Data will be ready after * several ticks, if write_pending is set. * * It may be deleted, but with this feature tcpdumps * look so _wonderfully_ clever, that I was not able * to stand against the temptation 8) --ANK */ tcp_schedule_ack(tp); tp->ack.lrcvtime = tcp_time_stamp; tp->ack.ato = TCP_ATO_MIN; tcp_incr_quickack(tp); tcp_enter_quickack_mode(tp); tcp_reset_xmit_timer(sk, TCP_TIME_DACK, TCP_DELACK_MAX); discard: __kfree_skb(skb); return 0; } else { tcp_send_ack(sk); } return -1; } /* No ACK in the segment */ if (th->rst) { /* rfc793: * "If the RST bit is set * * Otherwise (no ACK) drop the segment and return." */ goto discard_and_undo; } /* PAWS check. */ if (tp->ts_recent_stamp && tp->saw_tstamp && tcp_paws_check(tp, 0)) goto discard_and_undo; if (th->syn) { /* We see SYN without ACK. It is attempt of * simultaneous connect with crossed SYNs. * Particularly, it can be connect to self. */ tcp_set_state(sk, TCP_SYN_RECV); if (tp->saw_tstamp) { tp->tstamp_ok = 1; tcp_store_ts_recent(tp); tp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED; } else { tp->tcp_header_len = sizeof(struct tcphdr); } tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1; tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1; /* RFC1323: The window in SYN & SYN/ACK segments is * never scaled. */ tp->snd_wnd = ntohs(th->window); tp->snd_wl1 = TCP_SKB_CB(skb)->seq; tp->max_window = tp->snd_wnd; TCP_ECN_rcv_syn(tp, th); if (tp->ecn_flags&TCP_ECN_OK) sk->sk_no_largesend = 1; tcp_sync_mss(sk, tp->pmtu_cookie); tcp_initialize_rcv_mss(sk); tcp_send_synack(sk); #if 0 /* Note, we could accept data and URG from this segment. * There are no obstacles to make this. * * However, if we ignore data in ACKless segments sometimes, * we have no reasons to accept it sometimes. * Also, seems the code doing it in step6 of tcp_rcv_state_process * is not flawless. So, discard packet for sanity. * Uncomment this return to process the data. */ return -1; #else goto discard; #endif } /* "fifth, if neither of the SYN or RST bits is set then * drop the segment and return." */ discard_and_undo: tcp_clear_options(tp); tp->mss_clamp = saved_clamp; goto discard; reset_and_undo: tcp_clear_options(tp); tp->mss_clamp = saved_clamp; return 1; } /* * This function implements the receiving procedure of RFC 793 for * all states except ESTABLISHED and TIME_WAIT. * It's called from both tcp_v4_rcv and tcp_v6_rcv and should be * address independent. */ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb, struct tcphdr *th, unsigned len) { struct tcp_opt *tp = tcp_sk(sk); int queued = 0; tp->saw_tstamp = 0; switch (sk->sk_state) { case TCP_CLOSE: goto discard; case TCP_LISTEN: if(th->ack) return 1; if(th->rst) goto discard; if(th->syn) { if(tp->af_specific->conn_request(sk, skb) < 0) return 1; /* Now we have several options: In theory there is * nothing else in the frame. KA9Q has an option to * send data with the syn, BSD accepts data with the * syn up to the [to be] advertised window and * Solaris 2.1 gives you a protocol error. For now * we just ignore it, that fits the spec precisely * and avoids incompatibilities. It would be nice in * future to drop through and process the data. * * Now that TTCP is starting to be used we ought to * queue this data. * But, this leaves one open to an easy denial of * service attack, and SYN cookies can't defend * against this problem. So, we drop the data * in the interest of security over speed. */ goto discard; } goto discard; case TCP_SYN_SENT: queued = tcp_rcv_synsent_state_process(sk, skb, th, len); if (queued >= 0) return queued; /* Do step6 onward by hand. */ tcp_urg(sk, skb, th); __kfree_skb(skb); tcp_data_snd_check(sk); return 0; } if (tcp_fast_parse_options(skb, th, tp) && tp->saw_tstamp && tcp_paws_discard(tp, skb)) { if (!th->rst) { NET_INC_STATS_BH(PAWSEstabRejected); tcp_send_dupack(sk, skb); goto discard; } /* Reset is accepted even if it did not pass PAWS. */ } /* step 1: check sequence number */ if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) { if (!th->rst) tcp_send_dupack(sk, skb); goto discard; } /* step 2: check RST bit */ if(th->rst) { tcp_reset(sk); goto discard; } tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq); /* step 3: check security and precedence [ignored] */ /* step 4: * * Check for a SYN in window. */ if (th->syn && !before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) { NET_INC_STATS_BH(TCPAbortOnSyn); tcp_reset(sk); return 1; } /* step 5: check the ACK field */ if (th->ack) { int acceptable = tcp_ack(sk, skb, FLAG_SLOWPATH); switch(sk->sk_state) { case TCP_SYN_RECV: if (acceptable) { tp->copied_seq = tp->rcv_nxt; mb(); tcp_set_state(sk, TCP_ESTABLISHED); sk->sk_state_change(sk); /* Note, that this wakeup is only for marginal * crossed SYN case. Passively open sockets * are not waked up, because sk->sk_sleep == * NULL and sk->sk_socket == NULL. */ if (sk->sk_socket) { sk_wake_async(sk,0,POLL_OUT); } tp->snd_una = TCP_SKB_CB(skb)->ack_seq; tp->snd_wnd = ntohs(th->window) << tp->snd_wscale; tcp_init_wl(tp, TCP_SKB_CB(skb)->ack_seq, TCP_SKB_CB(skb)->seq); /* tcp_ack considers this ACK as duplicate * and does not calculate rtt. * Fix it at least with timestamps. */ if (tp->saw_tstamp && tp->rcv_tsecr && !tp->srtt) tcp_ack_saw_tstamp(tp, 0); if (tp->tstamp_ok) tp->advmss -= TCPOLEN_TSTAMP_ALIGNED; tcp_init_metrics(sk); tcp_initialize_rcv_mss(sk); tcp_init_buffer_space(sk); tcp_fast_path_on(tp); } else { return 1; } break; case TCP_FIN_WAIT1: if (tp->snd_una == tp->write_seq) { tcp_set_state(sk, TCP_FIN_WAIT2); sk->sk_shutdown |= SEND_SHUTDOWN; dst_confirm(sk->sk_dst_cache); if (!sock_flag(sk, SOCK_DEAD)) /* Wake up lingering close() */ sk->sk_state_change(sk); else { int tmo; if (tp->linger2 < 0 || (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq && after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt))) { tcp_done(sk); NET_INC_STATS_BH(TCPAbortOnData); return 1; } tmo = tcp_fin_time(tp); if (tmo > TCP_TIMEWAIT_LEN) { tcp_reset_keepalive_timer(sk, tmo - TCP_TIMEWAIT_LEN); } else if (th->fin || sock_owned_by_user(sk)) { /* Bad case. We could lose such FIN otherwise. * It is not a big problem, but it looks confusing * and not so rare event. We still can lose it now, * if it spins in bh_lock_sock(), but it is really * marginal case. */ tcp_reset_keepalive_timer(sk, tmo); } else { tcp_time_wait(sk, TCP_FIN_WAIT2, tmo); goto discard; } } } break; case TCP_CLOSING: if (tp->snd_una == tp->write_seq) { tcp_time_wait(sk, TCP_TIME_WAIT, 0); goto discard; } break; case TCP_LAST_ACK: if (tp->snd_una == tp->write_seq) { tcp_update_metrics(sk); tcp_done(sk); goto discard; } break; } } else goto discard; /* step 6: check the URG bit */ tcp_urg(sk, skb, th); /* step 7: process the segment text */ switch (sk->sk_state) { case TCP_CLOSE_WAIT: case TCP_CLOSING: case TCP_LAST_ACK: if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) break; case TCP_FIN_WAIT1: case TCP_FIN_WAIT2: /* RFC 793 says to queue data in these states, * RFC 1122 says we MUST send a reset. * BSD 4.4 also does reset. */ if (sk->sk_shutdown & RCV_SHUTDOWN) { if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq && after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) { NET_INC_STATS_BH(TCPAbortOnData); tcp_reset(sk); return 1; } } /* Fall through */ case TCP_ESTABLISHED: tcp_data_queue(sk, skb); queued = 1; break; } /* tcp_data could move socket to TIME-WAIT */ if (sk->sk_state != TCP_CLOSE) { tcp_data_snd_check(sk); tcp_ack_snd_check(sk); } if (!queued) { discard: __kfree_skb(skb); } return 0; }