/*- * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994, 1995 * The Regents of the University of California. All rights reserved. * Copyright (c) 2007-2008,2010 * Swinburne University of Technology, Melbourne, Australia. * Copyright (c) 2009-2010 Lawrence Stewart * Copyright (c) 2010 The FreeBSD Foundation * Copyright (c) 2010-2011 Juniper Networks, Inc. * All rights reserved. * * Portions of this software were developed at the Centre for Advanced Internet * Architectures, Swinburne University of Technology, by Lawrence Stewart, * James Healy and David Hayes, made possible in part by a grant from the Cisco * University Research Program Fund at Community Foundation Silicon Valley. * * Portions of this software were developed at the Centre for Advanced * Internet Architectures, Swinburne University of Technology, Melbourne, * Australia by David Hayes under sponsorship from the FreeBSD Foundation. * * Portions of this software were developed by Robert N. M. Watson under * contract to Juniper Networks, Inc. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * 4. Neither the name of the University nor the names of its contributors * may be used to endorse or promote products derived from this software * without specific prior written permission. * * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. * * @(#)tcp_input.c 8.12 (Berkeley) 5/24/95 */ /* * Determine a reasonable value for maxseg size. * If the route is known, check route for mtu. * If none, use an mss that can be handled on the outgoing interface * without forcing IP to fragment. If no route is found, route has no mtu, * or the destination isn't local, use a default, hopefully conservative * size (usually 512 or the default IP max size, but no more than the mtu * of the interface), as we can't discover anything about intervening * gateways or networks. We also initialize the congestion/slow start * window to be a single segment if the destination isn't local. * While looking at the routing entry, we also initialize other path-dependent * parameters from pre-set or cached values in the routing entry. * * Also take into account the space needed for options that we * send regularly. Make maxseg shorter by that amount to assure * that we can send maxseg amount of data even when the options * are present. Store the upper limit of the length of options plus * data in maxopd. * * NOTE that this routine is only called when we process an incoming * segment, or an ICMP need fragmentation datagram. Outgoing SYN/ACK MSS * settings are handled in tcp_mssopt(). */ #include #include #include #include "tcp.h" #include "tcp_fsm.h" #include "tcp_seq.h" #include "tcp_timer.h" #include "tcp_var.h" #include "tcp_fastopen.h" #include "../lib/bitmap.h" #include "../lib/cbuf.h" #include "icmp_var.h" #include "ip.h" #include "ip6.h" #include "sys/queue.h" #include "tcp_const.h" /* samkumar: Copied from in.h */ #define IPPROTO_DONE 267 /* samkumar: Copied from sys/libkern.h */ static int imax(int a, int b) { return (a > b ? a : b); } static int imin(int a, int b) { return (a < b ? a : b); } static int min(int a, int b) { return imin(a, b); } static void tcp_dooptions(struct tcpopt *, uint8_t *, int, int); static void tcp_do_segment(struct ip6_hdr* ip6, struct tcphdr *th, otMessage* msg, struct tcpcb *tp, int drop_hdrlen, int tlen, uint8_t iptos, struct tcplp_signals* sig); static void tcp_xmit_timer(struct tcpcb *, int); void tcp_hc_get(/*struct in_conninfo *inc*/ struct tcpcb* tp, struct hc_metrics_lite *hc_metrics_lite); static void tcp_newreno_partial_ack(struct tcpcb *, struct tcphdr *); /* * CC wrapper hook functions */ static inline void cc_ack_received(struct tcpcb *tp, struct tcphdr *th, uint16_t type) { tp->ccv->bytes_this_ack = BYTES_THIS_ACK(tp, th); if (tp->snd_cwnd <= tp->snd_wnd) tp->ccv->flags |= CCF_CWND_LIMITED; else tp->ccv->flags &= ~CCF_CWND_LIMITED; if (type == CC_ACK) { if (tp->snd_cwnd > tp->snd_ssthresh) { tp->t_bytes_acked += min(tp->ccv->bytes_this_ack, V_tcp_abc_l_var * tp->t_maxseg); if (tp->t_bytes_acked >= tp->snd_cwnd) { tp->t_bytes_acked -= tp->snd_cwnd; tp->ccv->flags |= CCF_ABC_SENTAWND; } } else { tp->ccv->flags &= ~CCF_ABC_SENTAWND; tp->t_bytes_acked = 0; } } if (CC_ALGO(tp)->ack_received != NULL) { /* XXXLAS: Find a way to live without this */ tp->ccv->curack = th->th_ack; CC_ALGO(tp)->ack_received(tp->ccv, type); } } static inline void cc_conn_init(struct tcpcb *tp) { struct hc_metrics_lite metrics; int rtt; /* * samkumar: remove locks, inpcb, and stats. */ /* samkumar: Used to take &inp->inp_inc as an argument. */ tcp_hc_get(tp, &metrics); if (tp->t_srtt == 0 && (rtt = metrics.rmx_rtt)) { tp->t_srtt = rtt; tp->t_rttbest = tp->t_srtt + TCP_RTT_SCALE; if (metrics.rmx_rttvar) { tp->t_rttvar = metrics.rmx_rttvar; } else { /* default variation is +- 1 rtt */ tp->t_rttvar = tp->t_srtt * TCP_RTTVAR_SCALE / TCP_RTT_SCALE; } TCPT_RANGESET(tp->t_rxtcur, ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1, tp->t_rttmin, TCPTV_REXMTMAX); } if (metrics.rmx_ssthresh) { /* * There's some sort of gateway or interface * buffer limit on the path. Use this to set * the slow start threshhold, but set the * threshold to no less than 2*mss. */ tp->snd_ssthresh = max(2 * tp->t_maxseg, metrics.rmx_ssthresh); } /* * Set the initial slow-start flight size. * * RFC5681 Section 3.1 specifies the default conservative values. * RFC3390 specifies slightly more aggressive values. * RFC6928 increases it to ten segments. * Support for user specified value for initial flight size. * * If a SYN or SYN/ACK was lost and retransmitted, we have to * reduce the initial CWND to one segment as congestion is likely * requiring us to be cautious. */ if (tp->snd_cwnd == 1) tp->snd_cwnd = tp->t_maxseg; /* SYN(-ACK) lost */ else if (V_tcp_initcwnd_segments) tp->snd_cwnd = min(V_tcp_initcwnd_segments * tp->t_maxseg, max(2 * tp->t_maxseg, V_tcp_initcwnd_segments * 1460)); else if (V_tcp_do_rfc3390) tp->snd_cwnd = min(4 * tp->t_maxseg, max(2 * tp->t_maxseg, 4380)); else { /* Per RFC5681 Section 3.1 */ if (tp->t_maxseg > 2190) tp->snd_cwnd = 2 * tp->t_maxseg; else if (tp->t_maxseg > 1095) tp->snd_cwnd = 3 * tp->t_maxseg; else tp->snd_cwnd = 4 * tp->t_maxseg; } if (CC_ALGO(tp)->conn_init != NULL) CC_ALGO(tp)->conn_init(tp->ccv); /* samkumar: print statement for debugging. Resurrect with DEBUG macro? */ #ifdef INSTRUMENT_TCP tcplp_sys_log("TCP CC_INIT %u %d %d", (unsigned int) tcplp_sys_get_millis(), (int) tp->snd_cwnd, (int) tp->snd_ssthresh); #endif } inline void cc_cong_signal(struct tcpcb *tp, struct tcphdr *th, uint32_t type) { /* samkumar: Remove locks and stats from this function. */ switch(type) { case CC_NDUPACK: if (!IN_FASTRECOVERY(tp->t_flags)) { tp->snd_recover = tp->snd_max; if (tp->t_flags & TF_ECN_PERMIT) tp->t_flags |= TF_ECN_SND_CWR; } break; case CC_ECN: if (!IN_CONGRECOVERY(tp->t_flags)) { tp->snd_recover = tp->snd_max; if (tp->t_flags & TF_ECN_PERMIT) tp->t_flags |= TF_ECN_SND_CWR; } break; case CC_RTO: tp->t_dupacks = 0; tp->t_bytes_acked = 0; EXIT_RECOVERY(tp->t_flags); /* * samkumar: I added the cast to uint64_t below to fix an OpenThread * code scanning alert relating to integer overflow in multiplication. */ tp->snd_ssthresh = max(2, min(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_maxseg) * ((uint64_t) tp->t_maxseg); tp->snd_cwnd = tp->t_maxseg; /* * samkumar: Stats for TCPlp: count the number of timeouts (RTOs). * I've commented this out (with #if 0) because it isn't part of TCP * functionality. At some point, we may want to bring it back to * measure performance. */ #if 0 tcplp_timeoutRexmitCnt++; #endif #ifdef INSTRUMENT_TCP tcplp_sys_log("TCP CC_RTO %u %d %d", (unsigned int) tcplp_sys_get_millis(), (int) tp->snd_cwnd, (int) tp->snd_ssthresh); #endif break; case CC_RTO_ERR: /* RTO was unnecessary, so reset everything. */ tp->snd_cwnd = tp->snd_cwnd_prev; tp->snd_ssthresh = tp->snd_ssthresh_prev; tp->snd_recover = tp->snd_recover_prev; if (tp->t_flags & TF_WASFRECOVERY) ENTER_FASTRECOVERY(tp->t_flags); if (tp->t_flags & TF_WASCRECOVERY) ENTER_CONGRECOVERY(tp->t_flags); tp->snd_nxt = tp->snd_max; tp->t_flags &= ~TF_PREVVALID; tp->t_badrxtwin = 0; #ifdef INSTRUMENT_TCP tcplp_sys_log("TCP CC_RTO_ERR %u %d %d", (unsigned int) tcplp_sys_get_millis(), (int) tp->snd_cwnd, (int) tp->snd_ssthresh); #endif break; } if (CC_ALGO(tp)->cong_signal != NULL) { if (th != NULL) tp->ccv->curack = th->th_ack; CC_ALGO(tp)->cong_signal(tp->ccv, type); } } static inline void cc_post_recovery(struct tcpcb *tp, struct tcphdr *th) { /* samkumar: remove lock */ /* XXXLAS: KASSERT that we're in recovery? */ if (CC_ALGO(tp)->post_recovery != NULL) { tp->ccv->curack = th->th_ack; CC_ALGO(tp)->post_recovery(tp->ccv); } /* XXXLAS: EXIT_RECOVERY ? */ tp->t_bytes_acked = 0; } /* * Indicate whether this ack should be delayed. We can delay the ack if * following conditions are met: * - There is no delayed ack timer in progress. * - Our last ack wasn't a 0-sized window. We never want to delay * the ack that opens up a 0-sized window. * - LRO wasn't used for this segment. We make sure by checking that the * segment size is not larger than the MSS. * - Delayed acks are enabled or this is a half-synchronized T/TCP * connection. */ #define DELAY_ACK(tp, tlen) \ ((!tcp_timer_active(tp, TT_DELACK) && \ (tp->t_flags & TF_RXWIN0SENT) == 0) && \ (tlen <= tp->t_maxopd) && \ (V_tcp_delack_enabled || (tp->t_flags & TF_NEEDSYN))) static inline void cc_ecnpkt_handler(struct tcpcb *tp, struct tcphdr *th, uint8_t iptos) { /* samkumar: remove lock */ if (CC_ALGO(tp)->ecnpkt_handler != NULL) { switch (iptos & IPTOS_ECN_MASK) { case IPTOS_ECN_CE: tp->ccv->flags |= CCF_IPHDR_CE; break; case IPTOS_ECN_ECT0: tp->ccv->flags &= ~CCF_IPHDR_CE; break; case IPTOS_ECN_ECT1: tp->ccv->flags &= ~CCF_IPHDR_CE; break; } if (th->th_flags & TH_CWR) tp->ccv->flags |= CCF_TCPHDR_CWR; else tp->ccv->flags &= ~CCF_TCPHDR_CWR; if (tp->t_flags & TF_DELACK) tp->ccv->flags |= CCF_DELACK; else tp->ccv->flags &= ~CCF_DELACK; CC_ALGO(tp)->ecnpkt_handler(tp->ccv); if (tp->ccv->flags & CCF_ACKNOW) tcp_timer_activate(tp, TT_DELACK, tcp_delacktime); } } /* * External function: look up an entry in the hostcache and fill out the * supplied TCP metrics structure. Fills in NULL when no entry was found or * a value is not set. */ /* * samkumar: This function is taken from tcp_hostcache.c. We have no host cache * in TCPlp, so I changed this to always act as if there is a miss. I removed * the first argument, formerly "struct in_coninfo *inc". */ void tcp_hc_get(struct tcpcb* tp, struct hc_metrics_lite *hc_metrics_lite) { bzero(hc_metrics_lite, sizeof(*hc_metrics_lite)); } /* * External function: look up an entry in the hostcache and return the * discovered path MTU. Returns NULL if no entry is found or value is not * set. */ /* * samkumar: This function is taken from tcp_hostcache.c. We have no host cache * in TCPlp, so I changed this to always act as if there is a miss. */ uint64_t tcp_hc_getmtu(struct tcpcb* tp) { return 0; } /* * Issue RST and make ACK acceptable to originator of segment. * The mbuf must still include the original packet header. * tp may be NULL. */ /* * samkumar: Original signature was: * static void tcp_dropwithreset(struct mbuf *m, struct tcphdr *th, struct tcpcb *tp, * int tlen, int rstreason) */ void tcp_dropwithreset(struct ip6_hdr* ip6, struct tcphdr *th, struct tcpcb *tp, otInstance* instance, int tlen, int rstreason) { /* * samkumar: I removed logic to skip this for broadcast or multicast * packets. In the FreeBSD version of this function, it would just * call m_freem(m), if m->m_flags has M_BCAST or M_MCAST set, and not * send a response packet. * I also removed bandwidth limiting. */ if (th->th_flags & TH_RST) return; /* tcp_respond consumes the mbuf chain. */ if (th->th_flags & TH_ACK) { tcp_respond(tp, instance, ip6, th, (tcp_seq) 0, th->th_ack, TH_RST); } else { if (th->th_flags & TH_SYN) tlen++; tcp_respond(tp, instance, ip6, th, th->th_seq + tlen, (tcp_seq) 0, TH_RST | TH_ACK); } return; } /* * TCP input handling is split into multiple parts: * tcp6_input is a thin wrapper around tcp_input for the extended * ip6_protox[] call format in ip6_input * tcp_input handles primary segment validation, inpcb lookup and * SYN processing on listen sockets * tcp_do_segment processes the ACK and text of the segment for * establishing, established and closing connections */ /* samkumar: The signature of this function was originally: tcp_input(struct mbuf **mp, int *offp, int proto) */ /* NOTE: tcp_fields_to_host(th) must be called before this function is called. */ int tcp_input(struct ip6_hdr* ip6, struct tcphdr* th, otMessage* msg, struct tcpcb* tp, struct tcpcb_listen* tpl, struct tcplp_signals* sig) { /* * samkumar: I significantly modified this function, compared to the * FreeBSD version. This function used to be reponsible for matching an * incoming TCP segment to its TCB. That functionality is now done by * TCPlp, and this function is only called once a match has been * identified. * * The tp and tpl arguments are used to indicate the match. Exactly one of * them must be NULL, and the other must be set. If tp is non-NULL, then * this function assumes that the packet was matched to an active socket * (connection endpoint). If tpl is non-NULL, then this function assumes * that this packet is a candidate match for a passive socket (listener) * and attempts to set up a new connection if the flags, sequence numbers, * etc. look OK. * * TCPlp assumes that the packets are IPv6, so I removed any logic specific * to IPv4. * * And of course, all code pertaining to locks and stats has been removed. */ int tlen = 0, off; int thflags; uint8_t iptos = 0; int drop_hdrlen; int rstreason = 0; struct tcpopt to; /* options in this segment */ uint8_t* optp = NULL; int optlen = 0; to.to_flags = 0; KASSERT(tp || tpl, ("One of tp and tpl must be positive")); /* * samkumar: Here, there used to be code that handled preprocessing: * calling m_pullup(m, sizeof(*ip6) + sizeof(*th)) to get the headers * contiguous in memory, setting the ip6 and th pointers, validating the * checksum, and dropping packets with unspecified source address. In * TCPlp, all of this is done for a packet before this function is called. */ tlen = ntohs(ip6->ip6_plen); // assume *off == sizeof(*ip6) /* * samkumar: Logic that handled IPv4 was deleted below. I won't add a * comment every time this is done, but I'm putting it here (one of the * first instances of this) for clarity. */ iptos = (ntohl(ip6->ip6_flow) >> 20) & 0xff; /* * Check that TCP offset makes sense, * pull out TCP options and adjust length. XXX */ off = (th->th_off_x2 >> TH_OFF_SHIFT) << 2; if (off < sizeof (struct tcphdr) || off > tlen) { goto drop; } tlen -= off; /* tlen is used instead of ti->ti_len */ /* samkumar: now, tlen is the length of the data */ if (off > sizeof (struct tcphdr)) { /* * samkumar: I removed a call to IP6_EXTHDR_CHECK, which I believe * checks for IPv6 extension headers. In TCPlp, we assume that these * are handled elsewhere in the networking stack, before the incoming * packet is processed at the TCP layer. I also removed the followup * calls to reassign the ip6 and th pointers. */ optlen = off - sizeof (struct tcphdr); optp = (uint8_t *)(th + 1); } thflags = th->th_flags; /* * samkumar: There used to be a call here to tcp_fields_to_host(th), which * changes the byte order of various fields to host format. I removed this * call from there and handle it in TCPlp, before calling this. The reason * is that it's possible for this function to be called twice by TCPlp's * logic (e.g., if the packet matches a TIME-WAIT socket this function * returns early, and the packet may then match a listening socket, at * which ppoint this function will be called again). Thus, any operations * like this, which mutate the packet itself, need to happen before calling * this function. */ /* * Delay dropping TCP, IP headers, IPv6 ext headers, and TCP options. * * samkumar: My TCP header is in a different buffer from the IP header. * drop_hdrlen is only meaningful as an offset into the TCP buffer, * because it is used to determine how much of the packet to discard * before copying it into the receive buffer. Therefore, my offset does * not include the length of IP header and options, only the length of * the TCP header and options. */ drop_hdrlen = /*off0 +*/ off; /* * Locate pcb for segment; if we're likely to add or remove a * connection then first acquire pcbinfo lock. There are three cases * where we might discover later we need a write lock despite the * flags: ACKs moving a connection out of the syncache, ACKs for a * connection in TIMEWAIT and SYNs not targeting a listening socket. */ /* * samkumar: Locking code is removed, invalidating most of the above * comment. */ /* * samkumar: The FreeBSD code at logic here to check m->m_flags for the * M_IP6_NEXTHOP flag, and search for the PACKET_TAG_IPFORWARD tag and * store it in fwd_tag if so. In TCPlp, we assume that the IPv6 layer of * the host network stack handles this kind of IPv6-related functionality, * so this logic has been removed. */ /* * samkumar: Here, there was code to match the packet to an inpcb and reply * with an RST segment if no match is found. This included taking the * fwd_tag into account, if set above (see the previous comment). I removed * this code because, in TCPlp, this is done before calling this function. */ /* * A previous connection in TIMEWAIT state is supposed to catch stray * or duplicate segments arriving late. If this segment was a * legitimate new connection attempt, the old INPCB gets removed and * we can try again to find a listening socket. * * At this point, due to earlier optimism, we may hold only an inpcb * lock, and not the inpcbinfo write lock. If so, we need to try to * acquire it, or if that fails, acquire a reference on the inpcb, * drop all locks, acquire a global write lock, and then re-acquire * the inpcb lock. We may at that point discover that another thread * has tried to free the inpcb, in which case we need to loop back * and try to find a new inpcb to deliver to. * * XXXRW: It may be time to rethink timewait locking. */ /* * samkumar: The original code checked inp->inp_flags & INP_TIMEWAIT. I * changed it to instead check tp->t_state, since we don't use inpcbs in * TCPlp. */ if (tp && tp->t_state == TCP6S_TIME_WAIT) { /* * samkumar: There's nothing wrong with the call to tcp_dooptions call * that I've commented out below; it's just that the modified * "tcp_twcheck" function no longer needs the options structure, so * I figured that there's no longer a good reason to parse the options. * In fact, this call was probably unnecessary even in the original * FreeBSD TCP code, since tcp_twcheck, even without my modifications, * did not use the pointer to the options structure! */ //if (thflags & TH_SYN) //tcp_dooptions(&to, optp, optlen, TO_SYN); /* * samkumar: The original code would "goto findpcb;" if this branch is * taken. Matching with a TCB is done outside of this function in * TCPlp, so we instead return a special value so that the caller knows * to try re-matching this packet to a socket. */ if (tcp_twcheck(tp,/*inp, &to,*/ th, /*m,*/ tlen)) return (RELOOKUP_REQUIRED); return (IPPROTO_DONE); } /* * The TCPCB may no longer exist if the connection is winding * down or it is in the CLOSED state. Either way we drop the * segment and send an appropriate response. */ /* * samkumar: There used to be code here that grabs the tp from the inpcb * and drops with reset if the connection is in the closed state or if * the tp is NULL. In TCPlp, the equivalent logic is done before entering * this function. There was also code here to handle TCP offload, which * TCPlp does not handle. */ /* * We've identified a valid inpcb, but it could be that we need an * inpcbinfo write lock but don't hold it. In this case, attempt to * acquire using the same strategy as the TIMEWAIT case above. If we * relock, we have to jump back to 'relocked' as the connection might * now be in TIMEWAIT. */ /* * samkumar: There used to be some code here for synchronization, MAC * management, and debugging. */ /* * When the socket is accepting connections (the INPCB is in LISTEN * state) we look into the SYN cache if this is a new connection * attempt or the completion of a previous one. Instead of checking * so->so_options to check if the socket is listening, we rely on the * arguments passed to this function (if tp == NULL, then tpl is not NULL * and is the matching listen socket). */ if (/*so->so_options & SO_ACCEPTCONN*/tp == NULL) { int tfo_cookie_valid = 0; uint64_t tfo_response_cookie; // int tfo_response_cookie_valid = 0; /* samkumar: NULL check isn't needed but prevents a compiler warning */ KASSERT(tpl != NULL && tpl->t_state == TCP6S_LISTEN, ("listen socket must be in listening state!")); /* * samkumar: There used to be some code here that checks if the * received segment is an ACK, and if so, searches the SYN cache to * find an entry whose connection establishment handshake this segment * completes. If such an entry is found, then a socket is created and * then tcp_do_segment is called to actually run the code to mark the * connection as established. If the received segment is an RST, then * that is processed in the syncache as well. In TCPlp we do not use a * SYN cache, so I've removed that code. The actual connection * establishment/processing logic happens in tcp_do_segment anyway, * which is called at the bottom of this function, so there's no need * to rewrite this code with special-case logic for that. */ /* * We can't do anything without SYN. */ if ((thflags & TH_SYN) == 0) { /* * samkumar: Here, and in several other instances, the FreeBSD * code would call tcp_log_addrs. Improving logging in these * edge cases in TCPlp is left for the future --- for now, I just * put "" where the address string would go. */ tcplp_sys_log("%s; %s: Listen socket: " "SYN is missing, segment ignored", "", __func__); goto dropunlock; } /* * (SYN|ACK) is bogus on a listen socket. */ if (thflags & TH_ACK) { /* samkumar: See above comment regarding tcp_log_addrs. */ tcplp_sys_log("%s; %s: Listen socket: " "SYN|ACK invalid, segment rejected", "", __func__); /* samkumar: Removed call to syncache_badack(&inc); */ rstreason = BANDLIM_RST_OPENPORT; goto dropwithreset; } /* * If the drop_synfin option is enabled, drop all * segments with both the SYN and FIN bits set. * This prevents e.g. nmap from identifying the * TCP/IP stack. * XXX: Poor reasoning. nmap has other methods * and is constantly refining its stack detection * strategies. * XXX: This is a violation of the TCP specification * and was used by RFC1644. */ if ((thflags & TH_FIN) && V_drop_synfin) { /* samkumar: See above comment regarding tcp_log_addrs. */ tcplp_sys_log("%s; %s: Listen socket: " "SYN|FIN segment ignored (based on " "sysctl setting)", "", __func__); goto dropunlock; } /* * Segment's flags are (SYN) or (SYN|FIN). * * TH_PUSH, TH_URG, TH_ECE, TH_CWR are ignored * as they do not affect the state of the TCP FSM. * The data pointed to by TH_URG and th_urp is ignored. */ KASSERT((thflags & (TH_RST|TH_ACK)) == 0, ("%s: Listen socket: TH_RST or TH_ACK set", __func__)); KASSERT(thflags & (TH_SYN), ("%s: Listen socket: TH_SYN not set", __func__)); /* * samkumar: There used to be some code here to reject incoming * SYN packets for deprecated interface addresses unless * V_ip6_use_deprecated is true. Rejecting the packet, in this case, * means to "goto dropwithreset". I removed this functionality. */ /* * Basic sanity checks on incoming SYN requests: * Don't respond if the destination is a link layer * broadcast according to RFC1122 4.2.3.10, p. 104. * If it is from this socket it must be forged. * Don't respond if the source or destination is a * global or subnet broad- or multicast address. * Note that it is quite possible to receive unicast * link-layer packets with a broadcast IP address. Use * in_broadcast() to find them. */ /* * samkumar: There used to be a sanity check that drops (via * "goto dropunlock") any broadcast or multicast packets. This check is * done by checking m->m_flags for (M_BAST|M_MCAST). The original * FreeBSD code for this has been removed (since checking m->m_flags * isn't really useful to us anyway). Note that other FreeBSD code that * checks for multicast source/destination addresses is retained below * (but only for the IPv6 case; the original FreeBSD code also handled * it for IPv4 addresses). */ if (th->th_dport == th->th_sport && IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst, &ip6->ip6_src)) { /* samkumar: See above comment regarding tcp_log_addrs. */ tcplp_sys_log("%s; %s: Listen socket: " "Connection attempt to/from self " "ignored", "", __func__); goto dropunlock; } if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) || IN6_IS_ADDR_MULTICAST(&ip6->ip6_src)) { /* samkumar: See above comment regarding tcp_log_addrs. */ tcplp_sys_log("%s; %s: Listen socket: " "Connection attempt from/to multicast " "address ignored", "", __func__); goto dropunlock; } /* * samkumar: The FreeBSD code would call * syncache_add(&inc, &to, th, inp, &so, m, NULL, NULL); * to add an entry to the SYN cache at this point. TCPlp doesn't use a * syncache, so we initialize the new socket right away. The code to * initialize the socket is taken from the syncache_socket function. */ /* * samkumar: As of FreeBSD 10.3, the syncache_add function returns * a flag indicating if a "fast open" code path should be taken. * In that case, there is a "goto" statement to the removed logic * above that calls tcp_do_segment after expanding a syncache entry. * Analogous logic is implemented below. */ tcp_dooptions(&to, optp, optlen, TO_SYN); /* * samkumar: TCP Fast Open logic taken from syncache_add in * FreeBSD 12.0. */ if (V_tcp_fastopen_server_enable && /*IS_FASTOPEN(tp->t_flags) && (tp->t_tfo_pending != NULL) && */ (to.to_flags & TOF_FASTOPEN)) { /* * Limit the number of pending TFO connections to * approximately half of the queue limit. This prevents TFO * SYN floods from starving the service by filling the * listen queue with bogus TFO connections. */ /* * samkumar: Since we let the application handle the listen * queue it doesn't make sense to limit the number of pending * TFO connections as above. Long term, I think the best fix * is to let applications know if an incoming connection is * TFO, so that they can handle the case appropriately (e.g., * by disabling TFO or by declining the connection). */ int result = tcp_fastopen_check_cookie(NULL, to.to_tfo_cookie, to.to_tfo_len, &tfo_response_cookie); tfo_cookie_valid = (result > 0); // tfo_response_cookie_valid = (result >= 0); } tp = tcplp_sys_accept_ready(tpl, &ip6->ip6_src, th->th_sport); // Try to allocate an active socket to accept into if (tp == NULL) { /* If we couldn't allocate, just ignore the SYN. */ return IPPROTO_DONE; } if (tp == (struct tcpcb *) -1) { rstreason = ECONNREFUSED; tp = NULL; goto dropwithreset; } sig->accepted_connection = tp; tcp_state_change(tp, TCPS_SYN_RECEIVED); tpmarkpassiveopen(tp); tp->iss = tcp_new_isn(tp); tp->irs = th->th_seq; tcp_rcvseqinit(tp); tcp_sendseqinit(tp); tp->snd_wl1 = th->th_seq; /* * samkumar: We remove the "+ 1"s below since we use * tcp_output to send the appropriate SYN-ACK. For * example, syncache_tfo_expand eliminates the "+ 1"s * too. My understanding is that syncache_socket has * the "+ 1"s because it's normally called once the * SYN-ACK has already been ACKed, which is not how * TCPlp operates. */ tp->snd_max = tp->iss/* + 1*/; tp->snd_nxt = tp->iss/* + 1*/; tp->rcv_up = th->th_seq + 1; tp->rcv_wnd = imin(imax(cbuf_free_space(&tp->recvbuf), 0), TCP_MAXWIN); tp->rcv_adv += tp->rcv_wnd; tp->last_ack_sent = tp->rcv_nxt; memcpy(&tp->laddr, &ip6->ip6_dst, sizeof(tp->laddr)); memcpy(&tp->faddr, &ip6->ip6_src, sizeof(tp->faddr)); tp->fport = th->th_sport; tp->lport = tpl->lport; /* * samkumar: Several of the checks below (taken from syncache_socket!) * check for flags in sc->sc_flags. They have been written to directly * check for the conditions on the TCP options structure or in the TCP * header that would ordinarily be used to set flags in sc->sc_flags * when adding an entry to the SYN cache. * * In effect, we combine the logic in syncache_add to set elements of * sc with the logic in syncache_socket to transfer state from sc * to the socket, but short-circuit the process to avoid ever storing * data in sc. Since this isn't just adding or deleting code, I decided * that it's better to keep comments indicating exactly how I composed * these two functions. */ tp->t_flags = tp->t_flags & (TF_NOPUSH | TF_NODELAY | TF_NOOPT); // tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY); // if (sc->sc_flags & SCF_NOOPT) // tp->t_flags |= TF_NOOPT; // else { if (!(tp->t_flags & TF_NOOPT) && V_tcp_do_rfc1323) { if (/*sc->sc_flags & SCF_WINSCALE*/to.to_flags & TOF_SCALE) { int wscale = 0; /* * Pick the smallest possible scaling factor that * will still allow us to scale up to sb_max, aka * kern.ipc.maxsockbuf. * * We do this because there are broken firewalls that * will corrupt the window scale option, leading to * the other endpoint believing that our advertised * window is unscaled. At scale factors larger than * 5 the unscaled window will drop below 1500 bytes, * leading to serious problems when traversing these * broken firewalls. * * With the default maxsockbuf of 256K, a scale factor * of 3 will be chosen by this algorithm. Those who * choose a larger maxsockbuf should watch out * for the compatiblity problems mentioned above. * * RFC1323: The Window field in a SYN (i.e., a * or ) segment itself is never scaled. */ /* * samkumar: The original logic, taken from syncache_add, is * listed below, commented out. In practice, we just use * wscale = 0 because in TCPlp we assume that the buffers * aren't big enough for window scaling to be all that useful. */ #if 0 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max) wscale++; #endif tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; tp->snd_scale = /*sc->sc_requested_s_scale*/to.to_wscale; tp->request_r_scale = wscale; } if (/*sc->sc_flags & SCF_TIMESTAMP*/to.to_flags & TOF_TS) { tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; tp->ts_recent = /*sc->sc_tsreflect*/to.to_tsval; tp->ts_recent_age = tcp_ts_getticks(); tp->ts_offset = /*sc->sc_tsoff*/0; // No syncookies, so this should always be 0 } /* * samkumar: there used to be code here that would set the * TF_SIGNATURE flag on tp->t_flags if SCF_SIGNATURE is set on * sc->sc_flags. I've left it in below, commented out. */ #if 0 #ifdef TCP_SIGNATURE if (sc->sc_flags & SCF_SIGNATURE) tp->t_flags |= TF_SIGNATURE; #endif #endif if (/*sc->sc_flags & SCF_SACK*/ to.to_flags & TOF_SACKPERM) tp->t_flags |= TF_SACK_PERMIT; } if (/*sc->sc_flags & SCF_ECN*/(th->th_flags & (TH_ECE|TH_CWR)) && V_tcp_do_ecn) tp->t_flags |= TF_ECN_PERMIT; /* * Set up MSS and get cached values from tcp_hostcache. * This might overwrite some of the defaults we just set. */ tcp_mss(tp, /*sc->sc_peer_mss*/(to.to_flags & TOF_MSS) ? to.to_mss : 0); if (tfo_cookie_valid) { /* * samkumar: The code below is taken from syncache_tfo_socket. * It calls syncache_socket (upon which the above code is based) * so it makes sense for this logic to go here. */ tp->t_flags |= TF_FASTOPEN; tp->t_tfo_cookie.server = tfo_response_cookie; tp->snd_max = tp->iss; tp->snd_nxt = tp->iss; // tp->tfo_pending = pending_counter; /* This would normally "goto" labeled code that calls tcp_do_segment. */ tcp_do_segment(ip6, th, msg, tp, drop_hdrlen, tlen, iptos, sig); tp->accepted_from = tpl; return (IPPROTO_DONE); } else { tp->t_flags |= TF_ACKNOW; // samkumar: my addition } tcp_output(tp); // to send the SYN-ACK tp->accepted_from = tpl; return (IPPROTO_DONE); } else if (tp->t_state == TCPS_LISTEN) { /* * When a listen socket is torn down the SO_ACCEPTCONN * flag is removed first while connections are drained * from the accept queue in a unlock/lock cycle of the * ACCEPT_LOCK, opening a race condition allowing a SYN * attempt go through unhandled. */ goto dropunlock; } KASSERT(tp, ("tp is still NULL!")); /* * samkumar: There used to be code here to verify TCP signatures. We don't * support TCP signatures in TCPlp. */ /* * Segment belongs to a connection in SYN_SENT, ESTABLISHED or later * state. tcp_do_segment() always consumes the mbuf chain, unlocks * the inpcb, and unlocks pcbinfo. */ tcp_do_segment(ip6, th, msg, tp, drop_hdrlen, tlen, iptos, sig); return (IPPROTO_DONE); /* * samkumar: Removed some locking and debugging code under all three of * these labels: dropwithreset, dropunlock, and drop. I also removed some * memory management code (e.g., calling m_freem(m) if m != NULL) since * the caller of this function will take care of that kind of memory * management in TCPlp. */ dropwithreset: /* * samkumar: The check against inp != NULL is now a check on tp != NULL. */ if (tp != NULL) { tcp_dropwithreset(ip6, th, tp, tp->instance, tlen, rstreason); } else tcp_dropwithreset(ip6, th, NULL, tpl->instance, tlen, rstreason); goto drop; dropunlock: drop: return (IPPROTO_DONE); } /* * samkumar: Original signature * static void * tcp_do_segment(struct mbuf *m, struct tcphdr *th, struct socket *so, * struct tcpcb *tp, int drop_hdrlen, int tlen, uint8_t iptos, * int ti_locked) */ static void tcp_do_segment(struct ip6_hdr* ip6, struct tcphdr *th, otMessage* msg, struct tcpcb *tp, int drop_hdrlen, int tlen, uint8_t iptos, struct tcplp_signals* sig) { /* * samkumar: All code pertaining to locks, stats, and debug has been * removed from this function. */ int thflags, acked, ourfinisacked, needoutput = 0; int rstreason, todrop, win; uint64_t tiwin; struct tcpopt to; int tfo_syn; uint32_t ticks = tcplp_sys_get_ticks(); otInstance* instance = tp->instance; thflags = th->th_flags; tp->sackhint.last_sack_ack = 0; /* * If this is either a state-changing packet or current state isn't * established, we require a write lock on tcbinfo. Otherwise, we * allow the tcbinfo to be in either alocked or unlocked, as the * caller may have unnecessarily acquired a write lock due to a race. */ /* samkumar: There used to be synchronization code here. */ KASSERT(tp->t_state > TCPS_LISTEN, ("%s: TCPS_LISTEN", __func__)); KASSERT(tp->t_state != TCPS_TIME_WAIT, ("%s: TCPS_TIME_WAIT", __func__)); /* * Segment received on connection. * Reset idle time and keep-alive timer. * XXX: This should be done after segment * validation to ignore broken/spoofed segs. */ tp->t_rcvtime = ticks; if (TCPS_HAVEESTABLISHED(tp->t_state)) tcp_timer_activate(tp, TT_KEEP, TP_KEEPIDLE(tp)); /* * Scale up the window into a 32-bit value. * For the SYN_SENT state the scale is zero. */ tiwin = th->th_win << tp->snd_scale; /* * TCP ECN processing. */ /* * samkumar: I intentionally left the TCPSTAT_INC lines below commented * out, to avoid altering the structure of the code too much by * reorganizing the switch statement. */ if (tp->t_flags & TF_ECN_PERMIT) { if (thflags & TH_CWR) tp->t_flags &= ~TF_ECN_SND_ECE; switch (iptos & IPTOS_ECN_MASK) { case IPTOS_ECN_CE: tp->t_flags |= TF_ECN_SND_ECE; //TCPSTAT_INC(tcps_ecn_ce); break; case IPTOS_ECN_ECT0: //TCPSTAT_INC(tcps_ecn_ect0); break; case IPTOS_ECN_ECT1: //TCPSTAT_INC(tcps_ecn_ect1); break; } /* Process a packet differently from RFC3168. */ cc_ecnpkt_handler(tp, th, iptos); /* Congestion experienced. */ if (thflags & TH_ECE) { cc_cong_signal(tp, th, CC_ECN); } } /* * Parse options on any incoming segment. */ tcp_dooptions(&to, (uint8_t *)(th + 1), ((th->th_off_x2 >> TH_OFF_SHIFT) << 2) - sizeof(struct tcphdr), (thflags & TH_SYN) ? TO_SYN : 0); /* * If echoed timestamp is later than the current time, * fall back to non RFC1323 RTT calculation. Normalize * timestamp if syncookies were used when this connection * was established. */ if ((to.to_flags & TOF_TS) && (to.to_tsecr != 0)) { to.to_tsecr -= tp->ts_offset; if (TSTMP_GT(to.to_tsecr, tcp_ts_getticks())) to.to_tsecr = 0; } /* * If timestamps were negotiated during SYN/ACK they should * appear on every segment during this session and vice versa. */ if ((tp->t_flags & TF_RCVD_TSTMP) && !(to.to_flags & TOF_TS)) { /* samkumar: See above comment regarding tcp_log_addrs. */ tcplp_sys_log("%s; %s: Timestamp missing, " "no action", "", __func__); } if (!(tp->t_flags & TF_RCVD_TSTMP) && (to.to_flags & TOF_TS)) { /* samkumar: See above comment regarding tcp_log_addrs. */ tcplp_sys_log("%s; %s: Timestamp not expected, " "no action", "", __func__); } /* * Process options only when we get SYN/ACK back. The SYN case * for incoming connections is handled in tcp_syncache. * According to RFC1323 the window field in a SYN (i.e., a * or ) segment itself is never scaled. * XXX this is traditional behavior, may need to be cleaned up. */ if (tp->t_state == TCPS_SYN_SENT && (thflags & TH_SYN)) { if ((to.to_flags & TOF_SCALE) && (tp->t_flags & TF_REQ_SCALE)) { tp->t_flags |= TF_RCVD_SCALE; tp->snd_scale = to.to_wscale; } /* * Initial send window. It will be updated with * the next incoming segment to the scaled value. */ tp->snd_wnd = th->th_win; if (to.to_flags & TOF_TS) { tp->t_flags |= TF_RCVD_TSTMP; tp->ts_recent = to.to_tsval; tp->ts_recent_age = tcp_ts_getticks(); } if (to.to_flags & TOF_MSS) tcp_mss(tp, to.to_mss); if ((tp->t_flags & TF_SACK_PERMIT) && (to.to_flags & TOF_SACKPERM) == 0) tp->t_flags &= ~TF_SACK_PERMIT; /* * samkumar: TCP Fast Open logic from FreeBSD 12.0. */ if (IS_FASTOPEN(tp->t_flags)) { if (to.to_flags & TOF_FASTOPEN) { uint16_t mss; if (to.to_flags & TOF_MSS) mss = to.to_mss; else /* * samkumar: The original code here would set * mss to either TCP6_MSS or TCP_MSS depending * on whether the INP_IPV6 flag is present in * tp->t_inpcb->inp_vflag. In TCPlp, we always * assume IPv6. */ mss = TCP6_MSS; tcp_fastopen_update_cache(tp, mss, to.to_tfo_len, to.to_tfo_cookie); } else tcp_fastopen_disable_path(tp); } } /* * Header prediction: check for the two common cases * of a uni-directional data xfer. If the packet has * no control flags, is in-sequence, the window didn't * change and we're not retransmitting, it's a * candidate. If the length is zero and the ack moved * forward, we're the sender side of the xfer. Just * free the data acked & wake any higher level process * that was blocked waiting for space. If the length * is non-zero and the ack didn't move, we're the * receiver side. If we're getting packets in-order * (the reassembly queue is empty), add the data to * the socket buffer and note that we need a delayed ack. * Make sure that the hidden state-flags are also off. * Since we check for TCPS_ESTABLISHED first, it can only * be TH_NEEDSYN. */ /* * samkumar: Replaced LIST_EMPTY(&tp->tsegq with the call to bmp_isempty). */ if (tp->t_state == TCPS_ESTABLISHED && th->th_seq == tp->rcv_nxt && (thflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK && tp->snd_nxt == tp->snd_max && tiwin && tiwin == tp->snd_wnd && ((tp->t_flags & (TF_NEEDSYN|TF_NEEDFIN)) == 0) && bmp_isempty(tp->reassbmp, REASSBMP_SIZE(tp)) && ((to.to_flags & TOF_TS) == 0 || TSTMP_GEQ(to.to_tsval, tp->ts_recent)) ) { /* * If last ACK falls within this segment's sequence numbers, * record the timestamp. * NOTE that the test is modified according to the latest * proposal of the tcplw@cray.com list (Braden 1993/04/26). */ if ((to.to_flags & TOF_TS) != 0 && SEQ_LEQ(th->th_seq, tp->last_ack_sent)) { tp->ts_recent_age = tcp_ts_getticks(); tp->ts_recent = to.to_tsval; } if (tlen == 0) { if (SEQ_GT(th->th_ack, tp->snd_una) && SEQ_LEQ(th->th_ack, tp->snd_max) && !IN_RECOVERY(tp->t_flags) && (to.to_flags & TOF_SACK) == 0 && TAILQ_EMPTY(&tp->snd_holes)) { /* * This is a pure ack for outstanding data. */ /* * "bad retransmit" recovery. */ if (tp->t_rxtshift == 1 && tp->t_flags & TF_PREVVALID && (int)(ticks - tp->t_badrxtwin) < 0) { cc_cong_signal(tp, th, CC_RTO_ERR); } /* * Recalculate the transmit timer / rtt. * * Some boxes send broken timestamp replies * during the SYN+ACK phase, ignore * timestamps of 0 or we could calculate a * huge RTT and blow up the retransmit timer. */ if ((to.to_flags & TOF_TS) != 0 && to.to_tsecr) { uint32_t t; t = tcp_ts_getticks() - to.to_tsecr; if (!tp->t_rttlow || tp->t_rttlow > t) tp->t_rttlow = t; tcp_xmit_timer(tp, TCP_TS_TO_TICKS(t) + 1); } else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq)) { if (!tp->t_rttlow || tp->t_rttlow > ticks - tp->t_rtttime) tp->t_rttlow = ticks - tp->t_rtttime; tcp_xmit_timer(tp, ticks - tp->t_rtttime); } acked = BYTES_THIS_ACK(tp, th); /* * samkumar: Replaced sbdrop(&so->so_snd, acked) with this call * to lbuf_pop. */ { uint32_t poppedbytes = lbuf_pop(&tp->sendbuf, acked, &sig->links_popped); KASSERT(poppedbytes == acked, ("More bytes were acked than are in the send buffer")); sig->bytes_acked += poppedbytes; } if (SEQ_GT(tp->snd_una, tp->snd_recover) && SEQ_LEQ(th->th_ack, tp->snd_recover)) tp->snd_recover = th->th_ack - 1; /* * Let the congestion control algorithm update * congestion control related information. This * typically means increasing the congestion * window. */ cc_ack_received(tp, th, CC_ACK); tp->snd_una = th->th_ack; /* * Pull snd_wl2 up to prevent seq wrap relative * to th_ack. */ tp->snd_wl2 = th->th_ack; tp->t_dupacks = 0; /* * If all outstanding data are acked, stop * retransmit timer, otherwise restart timer * using current (possibly backed-off) value. * If process is waiting for space, * wakeup/selwakeup/signal. If data * are ready to send, let tcp_output * decide between more output or persist. */ if (tp->snd_una == tp->snd_max) tcp_timer_activate(tp, TT_REXMT, 0); else if (!tcp_timer_active(tp, TT_PERSIST)) tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur); /* * samkumar: There used to be a call to sowwakeup(so); here, * which wakes up any threads waiting for the socket to * become ready for writing. TCPlp handles its send buffer * differently so we do not need to replace this call with * specialized code to handle this. */ /* * samkumar: Replaced sbavail(&so->so_snd) with this call to * lbuf_used_space. */ if (lbuf_used_space(&tp->sendbuf)) (void) tcp_output(tp); goto check_delack; } } else if (th->th_ack == tp->snd_una && /* * samkumar: Replaced sbspace(&so->so_rcv) with this call to * cbuf_free_space. */ tlen <= cbuf_free_space(&tp->recvbuf)) { /* * This is a pure, in-sequence data packet with * nothing on the reassembly queue and we have enough * buffer space to take it. */ /* Clean receiver SACK report if present */ if ((tp->t_flags & TF_SACK_PERMIT) && tp->rcv_numsacks) tcp_clean_sackreport(tp); tp->rcv_nxt += tlen; /* * Pull snd_wl1 up to prevent seq wrap relative to * th_seq. */ tp->snd_wl1 = th->th_seq; /* * Pull rcv_up up to prevent seq wrap relative to * rcv_nxt. */ tp->rcv_up = tp->rcv_nxt; /* * Automatic sizing of receive socket buffer. Often the send * buffer size is not optimally adjusted to the actual network * conditions at hand (delay bandwidth product). Setting the * buffer size too small limits throughput on links with high * bandwidth and high delay (eg. trans-continental/oceanic links). * * On the receive side the socket buffer memory is only rarely * used to any significant extent. This allows us to be much * more aggressive in scaling the receive socket buffer. For * the case that the buffer space is actually used to a large * extent and we run out of kernel memory we can simply drop * the new segments; TCP on the sender will just retransmit it * later. Setting the buffer size too big may only consume too * much kernel memory if the application doesn't read() from * the socket or packet loss or reordering makes use of the * reassembly queue. * * The criteria to step up the receive buffer one notch are: * 1. Application has not set receive buffer size with * SO_RCVBUF. Setting SO_RCVBUF clears SB_AUTOSIZE. * 2. the number of bytes received during the time it takes * one timestamp to be reflected back to us (the RTT); * 3. received bytes per RTT is within seven eighth of the * current socket buffer size; * 4. receive buffer size has not hit maximal automatic size; * * This algorithm does one step per RTT at most and only if * we receive a bulk stream w/o packet losses or reorderings. * Shrinking the buffer during idle times is not necessary as * it doesn't consume any memory when idle. * * TODO: Only step up if the application is actually serving * the buffer to better manage the socket buffer resources. */ /* * samkumar: There used to be code here to dynamically size the * receive buffer (tp->rfbuf_ts, rp->rfbuf_cnt, and the local * newsize variable). In TCPlp, we don't support this, as the user * allocates the receive buffer and its size can't be changed here. * Therefore, I removed the code that does this. Note that the * actual resizing of the buffer is done using sbreserve_locked, * whose call comes later (not exactly where this comment is). */ /* Add data to socket buffer. */ /* * samkumar: The code that was here would just free the mbuf * (with m_freem(m)) if SBS_CANTRCVMORE is set in * so->so_rcv.sb_state. Otherwise, it would cut drop_hdrlen bytes * from the mbuf (using m_adj(m, drop_hdrlen)) to discard the * headers and then append the mbuf to the receive buffer using * sbappendstream_locked(&so->so_rcv, m, 0). I've rewritten this * to work the TCPlp way. The check to so->so_rcv.sb_state is * replaced by a tcpiscantrcv call, and we copy bytes into * TCPlp's circular buffer (since we designed it to avoid * having dynamically-allocated memory for the receive buffer). */ if (!tpiscantrcv(tp)) { cbuf_write(&tp->recvbuf, msg, otMessageGetOffset(msg) + drop_hdrlen, tlen, cbuf_copy_from_message); if (tlen > 0) { sig->recvbuf_added = true; } } else { /* * samkumar: We already know tlen != 0, so if we got here, then * it means that we got data after we called SHUT_RD, or after * receiving a FIN. I'm going to drop the connection in this * case. I think FreeBSD might have just dropped the packet * silently, but Linux handles it this way; this seems to be * the right approach to me. */ tcp_drop(tp, ECONNABORTED); goto drop; } /* NB: sorwakeup_locked() does an implicit unlock. */ /* * samkumar: There used to be a call to sorwakeup_locked(so); here, * which wakes up any threads waiting for the socket to become * become ready for reading. TCPlp handles its buffering * differently so we do not need to replace this call with * specialized code to handle this. */ if (DELAY_ACK(tp, tlen)) { tp->t_flags |= TF_DELACK; } else { tp->t_flags |= TF_ACKNOW; tcp_output(tp); } goto check_delack; } } /* * Calculate amount of space in receive window, * and then do TCP input processing. * Receive window is amount of space in rcv queue, * but not less than advertised window. */ /* samkumar: Replaced sbspace(&so->so_rcv) with call to cbuf_free_space. */ win = cbuf_free_space(&tp->recvbuf); if (win < 0) win = 0; tp->rcv_wnd = imax(win, (int)(tp->rcv_adv - tp->rcv_nxt)); /* Reset receive buffer auto scaling when not in bulk receive mode. */ /* samkumar: Removed this receive buffer autoscaling code. */ switch (tp->t_state) { /* * If the state is SYN_RECEIVED: * if seg contains an ACK, but not for our SYN/ACK, send a RST. * (Added by Sam) if seg is resending the original SYN, resend the SYN/ACK */ /* * samkumar: If we receive a retransmission of the original SYN, then * resend the SYN/ACK segment. This case was probably handled by the * SYN cache. Because TCPlp does not use a SYN cache, we need to write * custom logic for it. It is handled in the "else if" clause below. */ case TCPS_SYN_RECEIVED: if ((thflags & TH_ACK) && (SEQ_LEQ(th->th_ack, tp->snd_una) || SEQ_GT(th->th_ack, tp->snd_max))) { rstreason = BANDLIM_RST_OPENPORT; goto dropwithreset; } else if (!IS_FASTOPEN(tp->t_flags) && (thflags & TH_SYN) && !(thflags & TH_ACK) && (th->th_seq == tp->irs)) { tp->t_flags |= TF_ACKNOW; } /* * samkumar: TCP Fast Open Logic from FreeBSD 12.0. */ if (IS_FASTOPEN(tp->t_flags)) { /* * When a TFO connection is in SYN_RECEIVED, the * only valid packets are the initial SYN, a * retransmit/copy of the initial SYN (possibly with * a subset of the original data), a valid ACK, a * FIN, or a RST. */ if ((thflags & (TH_SYN|TH_ACK)) == (TH_SYN|TH_ACK)) { rstreason = BANDLIM_RST_OPENPORT; goto dropwithreset; } else if (thflags & TH_SYN) { /* non-initial SYN is ignored */ if ((tcp_timer_active(tp, TT_DELACK) || tcp_timer_active(tp, TT_REXMT))) goto drop; } else if (!(thflags & (TH_ACK|TH_FIN|TH_RST))) { goto drop; } } break; /* * If the state is SYN_SENT: * if seg contains an ACK, but not for our SYN, drop the input. * if seg contains a RST, then drop the connection. * if seg does not contain SYN, then drop it. * Otherwise this is an acceptable SYN segment * initialize tp->rcv_nxt and tp->irs * if seg contains ack then advance tp->snd_una * if seg contains an ECE and ECN support is enabled, the stream * is ECN capable. * if SYN has been acked change to ESTABLISHED else SYN_RCVD state * arrange for segment to be acked (eventually) * continue processing rest of data/controls, beginning with URG */ case TCPS_SYN_SENT: if ((thflags & TH_ACK) && (SEQ_LEQ(th->th_ack, tp->iss) || SEQ_GT(th->th_ack, tp->snd_max))) { rstreason = BANDLIM_UNLIMITED; goto dropwithreset; } if ((thflags & (TH_ACK|TH_RST)) == (TH_ACK|TH_RST)) { tp = tcp_drop(tp, ECONNREFUSED); } if (thflags & TH_RST) goto drop; if (!(thflags & TH_SYN)) goto drop; tp->irs = th->th_seq; tcp_rcvseqinit(tp); if (thflags & TH_ACK) { int tfo_partial_ack = 0; /* * samkumar: Removed call to soisconnected(so), since TCPlp has its * own buffering. */ /* Do window scaling on this connection? */ if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) == (TF_RCVD_SCALE|TF_REQ_SCALE)) { tp->rcv_scale = tp->request_r_scale; } tp->rcv_adv += imin(tp->rcv_wnd, TCP_MAXWIN << tp->rcv_scale); tp->snd_una++; /* SYN is acked */ /* * If not all the data that was sent in the TFO SYN * has been acked, resend the remainder right away. */ if (IS_FASTOPEN(tp->t_flags) && (tp->snd_una != tp->snd_max)) { tp->snd_nxt = th->th_ack; tfo_partial_ack = 1; } /* * If there's data, delay ACK; if there's also a FIN * ACKNOW will be turned on later. */ if (DELAY_ACK(tp, tlen) && tlen != 0 && !tfo_partial_ack) tcp_timer_activate(tp, TT_DELACK, tcp_delacktime); else tp->t_flags |= TF_ACKNOW; if ((thflags & TH_ECE) && V_tcp_do_ecn) { tp->t_flags |= TF_ECN_PERMIT; } /* * Received in SYN_SENT[*] state. * Transitions: * SYN_SENT --> ESTABLISHED * SYN_SENT* --> FIN_WAIT_1 */ tp->t_starttime = ticks; if (tp->t_flags & TF_NEEDFIN) { tcp_state_change(tp, TCPS_FIN_WAIT_1); tp->t_flags &= ~TF_NEEDFIN; thflags &= ~TH_SYN; } else { tcp_state_change(tp, TCPS_ESTABLISHED); /* samkumar: Set conn_established signal for TCPlp. */ sig->conn_established = true; cc_conn_init(tp); tcp_timer_activate(tp, TT_KEEP, TP_KEEPIDLE(tp)); } } else { /* * Received initial SYN in SYN-SENT[*] state => * simultaneous open. * If it succeeds, connection is * half-synchronized. * Otherwise, do 3-way handshake: * SYN-SENT -> SYN-RECEIVED * SYN-SENT* -> SYN-RECEIVED* */ tp->t_flags |= (TF_ACKNOW | TF_NEEDSYN); tcp_timer_activate(tp, TT_REXMT, 0); tcp_state_change(tp, TCPS_SYN_RECEIVED); /* * samkumar: We would have incremented snd_next in tcp_output when * we sent the original SYN, so decrement it here. (Another * consequence of removing the SYN cache.) */ tp->snd_nxt--; } /* * Advance th->th_seq to correspond to first data byte. * If data, trim to stay within window, * dropping FIN if necessary. */ th->th_seq++; if (tlen > tp->rcv_wnd) { todrop = tlen - tp->rcv_wnd; /* * samkumar: I removed a call to m_adj(m, -todrop), which intends * to trim the data so it fits in the window. We can just read less * when copying into the receive buffer in TCPlp, so we don't need * to do this. */ (void) todrop; /* samkumar: Prevent a compiler warning */ tlen = tp->rcv_wnd; thflags &= ~TH_FIN; } tp->snd_wl1 = th->th_seq - 1; tp->rcv_up = th->th_seq; /* * Client side of transaction: already sent SYN and data. * If the remote host used T/TCP to validate the SYN, * our data will be ACK'd; if so, enter normal data segment * processing in the middle of step 5, ack processing. * Otherwise, goto step 6. */ if (thflags & TH_ACK) goto process_ACK; goto step6; /* * If the state is LAST_ACK or CLOSING or TIME_WAIT: * do normal processing. * * NB: Leftover from RFC1644 T/TCP. Cases to be reused later. */ case TCPS_LAST_ACK: case TCPS_CLOSING: break; /* continue normal processing */ } /* * States other than LISTEN or SYN_SENT. * First check the RST flag and sequence number since reset segments * are exempt from the timestamp and connection count tests. This * fixes a bug introduced by the Stevens, vol. 2, p. 960 bugfix * below which allowed reset segments in half the sequence space * to fall though and be processed (which gives forged reset * segments with a random sequence number a 50 percent chance of * killing a connection). * Then check timestamp, if present. * Then check the connection count, if present. * Then check that at least some bytes of segment are within * receive window. If segment begins before rcv_nxt, * drop leading data (and SYN); if nothing left, just ack. */ if (thflags & TH_RST) { /* * RFC5961 Section 3.2 * * - RST drops connection only if SEG.SEQ == RCV.NXT. * - If RST is in window, we send challenge ACK. * * Note: to take into account delayed ACKs, we should * test against last_ack_sent instead of rcv_nxt. * Note 2: we handle special case of closed window, not * covered by the RFC. */ if ((SEQ_GEQ(th->th_seq, tp->last_ack_sent) && SEQ_LT(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) || (tp->rcv_wnd == 0 && tp->last_ack_sent == th->th_seq)) { /* * samkumar: This if statement used to also be prefaced with * "V_tcp_insecure_rst ||". But I removed it, since there's no * reason to support an insecure option in TCPlp (my guess is that * FreeBSD supported it for legacy reasons). */ if (tp->last_ack_sent == th->th_seq) { /* * samkumar: Normally, the error number would be stored in * so->so_error. Instead, we put it in this "droperror" local * variable and then pass it to tcplp_sys_connection_lost. */ int droperror = 0; /* Drop the connection. */ switch (tp->t_state) { case TCPS_SYN_RECEIVED: droperror = ECONNREFUSED; goto close; case TCPS_ESTABLISHED: case TCPS_FIN_WAIT_1: case TCPS_FIN_WAIT_2: case TCPS_CLOSE_WAIT: droperror = ECONNRESET; close: tcp_state_change(tp, TCPS_CLOSED); /* FALLTHROUGH */ default: tp = tcp_close(tp); tcplp_sys_connection_lost(tp, droperror); } } else { /* Send challenge ACK. */ tcp_respond(tp, tp->instance, ip6, th, tp->rcv_nxt, tp->snd_nxt, TH_ACK); tp->last_ack_sent = tp->rcv_nxt; } } goto drop; } /* * RFC5961 Section 4.2 * Send challenge ACK for any SYN in synchronized state. */ /* * samkumar: I added the check for the SYN-RECEIVED state in this if * statement (another consequence of removing the SYN cache). */ if ((thflags & TH_SYN) && tp->t_state != TCPS_SYN_SENT && tp->t_state != TCP6S_SYN_RECEIVED) { /* * samkumar: The modern way to handle this is to send a Challenge ACK. * FreeBSD supports this, but it also has this V_tcp_insecure_syn * options that will cause it to drop the connection if the SYN falls * in the receive window. In TCPlp we *only* support Challenge ACKs * (the secure way of doing it), so I've removed code for the insecure * way. (Presumably the reason why FreeBSD supports the insecure way is * for legacy code, which we don't really care about in TCPlp). */ /* Send challenge ACK. */ tcplp_sys_log("Sending challenge ACK"); tcp_respond(tp, tp->instance, ip6, th, tp->rcv_nxt, tp->snd_nxt, TH_ACK); tp->last_ack_sent = tp->rcv_nxt; goto drop; } /* * RFC 1323 PAWS: If we have a timestamp reply on this segment * and it's less than ts_recent, drop it. */ if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent && TSTMP_LT(to.to_tsval, tp->ts_recent)) { /* Check to see if ts_recent is over 24 days old. */ if (tcp_ts_getticks() - tp->ts_recent_age > TCP_PAWS_IDLE) { /* * Invalidate ts_recent. If this segment updates * ts_recent, the age will be reset later and ts_recent * will get a valid value. If it does not, setting * ts_recent to zero will at least satisfy the * requirement that zero be placed in the timestamp * echo reply when ts_recent isn't valid. The * age isn't reset until we get a valid ts_recent * because we don't want out-of-order segments to be * dropped when ts_recent is old. */ tp->ts_recent = 0; } else { if (tlen) goto dropafterack; goto drop; } } /* * In the SYN-RECEIVED state, validate that the packet belongs to * this connection before trimming the data to fit the receive * window. Check the sequence number versus IRS since we know * the sequence numbers haven't wrapped. This is a partial fix * for the "LAND" DoS attack. */ if (tp->t_state == TCPS_SYN_RECEIVED && SEQ_LT(th->th_seq, tp->irs)) { rstreason = BANDLIM_RST_OPENPORT; goto dropwithreset; } todrop = tp->rcv_nxt - th->th_seq; if (todrop > 0) { if (thflags & TH_SYN) { thflags &= ~TH_SYN; th->th_seq++; if (th->th_urp > 1) th->th_urp--; else thflags &= ~TH_URG; todrop--; } /* * Following if statement from Stevens, vol. 2, p. 960. */ if (todrop > tlen || (todrop == tlen && (thflags & TH_FIN) == 0)) { /* * Any valid FIN must be to the left of the window. * At this point the FIN must be a duplicate or out * of sequence; drop it. */ thflags &= ~TH_FIN; /* * Send an ACK to resynchronize and drop any data. * But keep on processing for RST or ACK. */ tp->t_flags |= TF_ACKNOW; todrop = tlen; } /* samkumar: There was an else case that only collected stats. */ drop_hdrlen += todrop; /* drop from the top afterwards */ th->th_seq += todrop; tlen -= todrop; if (th->th_urp > todrop) th->th_urp -= todrop; else { thflags &= ~TH_URG; th->th_urp = 0; } } /* * If new data are received on a connection after the * user processes are gone, then RST the other end. */ /* * samkumar: TCPlp is designed for embedded systems where there is no * concept of a "process" that has allocated a TCP socket. Therefore, we * do not implement the functionality in the above comment (the code for * it used to be here, and I removed it). */ /* * If segment ends after window, drop trailing data * (and PUSH and FIN); if nothing left, just ACK. */ todrop = (th->th_seq + tlen) - (tp->rcv_nxt + tp->rcv_wnd); if (todrop > 0) { if (todrop >= tlen) { /* * If window is closed can only take segments at * window edge, and have to drop data and PUSH from * incoming segments. Continue processing, but * remember to ack. Otherwise, drop segment * and ack. */ if (tp->rcv_wnd == 0 && th->th_seq == tp->rcv_nxt) { tp->t_flags |= TF_ACKNOW; } else goto dropafterack; } /* * samkumar: I removed a call to m_adj(m, -todrop), which intends * to trim the data so it fits in the window. We can just read less * when copying into the receive buffer in TCPlp, so we don't need * to do this. Subtracting it from tlen gives us enough information to * do this later. In FreeBSD, this isn't possible because the mbuf * itself becomes part of the receive buffer, so the mbuf has to be * trimmed in order for this to work out. */ tlen -= todrop; thflags &= ~(TH_PUSH|TH_FIN); } /* * If last ACK falls within this segment's sequence numbers, * record its timestamp. * NOTE: * 1) That the test incorporates suggestions from the latest * proposal of the tcplw@cray.com list (Braden 1993/04/26). * 2) That updating only on newer timestamps interferes with * our earlier PAWS tests, so this check should be solely * predicated on the sequence space of this segment. * 3) That we modify the segment boundary check to be * Last.ACK.Sent <= SEG.SEQ + SEG.Len * instead of RFC1323's * Last.ACK.Sent < SEG.SEQ + SEG.Len, * This modified check allows us to overcome RFC1323's * limitations as described in Stevens TCP/IP Illustrated * Vol. 2 p.869. In such cases, we can still calculate the * RTT correctly when RCV.NXT == Last.ACK.Sent. */ if ((to.to_flags & TOF_TS) != 0 && SEQ_LEQ(th->th_seq, tp->last_ack_sent) && SEQ_LEQ(tp->last_ack_sent, th->th_seq + tlen + ((thflags & (TH_SYN|TH_FIN)) != 0))) { tp->ts_recent_age = tcp_ts_getticks(); tp->ts_recent = to.to_tsval; } /* * If the ACK bit is off: if in SYN-RECEIVED state or SENDSYN * flag is on (half-synchronized state), then queue data for * later processing; else drop segment and return. */ if ((thflags & TH_ACK) == 0) { if (tp->t_state == TCPS_SYN_RECEIVED || (tp->t_flags & TF_NEEDSYN)) { if (tp->t_state == TCPS_SYN_RECEIVED && IS_FASTOPEN(tp->t_flags)) { tp->snd_wnd = tiwin; cc_conn_init(tp); } goto step6; } else if (tp->t_flags & TF_ACKNOW) goto dropafterack; else goto drop; } tcplp_sys_log("Processing ACK"); /* * Ack processing. */ switch (tp->t_state) { /* * In SYN_RECEIVED state, the ack ACKs our SYN, so enter * ESTABLISHED state and continue processing. * The ACK was checked above. */ case TCPS_SYN_RECEIVED: /* * samkumar: Removed call to soisconnected(so), since TCPlp has its * own buffering. */ /* Do window scaling? */ if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) == (TF_RCVD_SCALE|TF_REQ_SCALE)) { tp->rcv_scale = tp->request_r_scale; tp->snd_wnd = tiwin; } /* * Make transitions: * SYN-RECEIVED -> ESTABLISHED * SYN-RECEIVED* -> FIN-WAIT-1 */ tp->t_starttime = ticks; /* * samkumar: I'm eliminating the TFO pending counter. */ if (IS_FASTOPEN(tp->t_flags)/* && tp->t_tfo_pending */) {\ /* tcp_fastopen_decrement_counter(tp->t_tfo_pending); tp->t_tfo_pending = NULL; */ /* * Account for the ACK of our SYN prior to * regular ACK processing below. */ tp->snd_una++; } if (tp->t_flags & TF_NEEDFIN) { tcp_state_change(tp, TCPS_FIN_WAIT_1); tp->t_flags &= ~TF_NEEDFIN; } else { tcp_state_change(tp, TCPS_ESTABLISHED); /* samkumar: Set conn_established signal for TCPlp. */ sig->conn_established = true; /* * TFO connections call cc_conn_init() during SYN * processing. Calling it again here for such * connections is not harmless as it would undo the * snd_cwnd reduction that occurs when a TFO SYN|ACK * is retransmitted. */ if (!IS_FASTOPEN(tp->t_flags)) cc_conn_init(tp); tcp_timer_activate(tp, TT_KEEP, TP_KEEPIDLE(tp)); /* * samkumar: I added this check to account for simultaneous open. * If this socket was opened actively, then the fact that we are * in SYN-RECEIVED indicates that we are in simultaneous open. * Therefore, don't ACK the SYN-ACK (unless it contains data or * something, which will be processed later). */ if (!tpispassiveopen(tp)) { tp->t_flags &= ~TF_ACKNOW; } else { /* * samkumar: Otherwise, we entered the ESTABLISHED state by * accepting a connection, so call the appropriate callback in * TCPlp. TODO: consider using signals to handle this? */ bool accepted = tcplp_sys_accepted_connection(tp->accepted_from, tp, &ip6->ip6_src, th->th_sport); if (!accepted) { rstreason = ECONNREFUSED; goto dropwithreset; } } } /* * If segment contains data or ACK, will call tcp_reass() * later; if not, do so now to pass queued data to user. */ if (tlen == 0 && (thflags & TH_FIN) == 0) (void) tcp_reass(tp, (struct tcphdr *)0, 0, (otMessage*)0, 0, sig); tp->snd_wl1 = th->th_seq - 1; /* FALLTHROUGH */ /* * In ESTABLISHED state: drop duplicate ACKs; ACK out of range * ACKs. If the ack is in the range * tp->snd_una < th->th_ack <= tp->snd_max * then advance tp->snd_una to th->th_ack and drop * data from the retransmission queue. If this ACK reflects * more up to date window information we update our window information. */ case TCPS_ESTABLISHED: case TCPS_FIN_WAIT_1: case TCPS_FIN_WAIT_2: case TCPS_CLOSE_WAIT: case TCPS_CLOSING: case TCPS_LAST_ACK: if (SEQ_GT(th->th_ack, tp->snd_max)) { goto dropafterack; } if ((tp->t_flags & TF_SACK_PERMIT) && ((to.to_flags & TOF_SACK) || !TAILQ_EMPTY(&tp->snd_holes))) tcp_sack_doack(tp, &to, th->th_ack); if (SEQ_LEQ(th->th_ack, tp->snd_una)) { if (tlen == 0 && tiwin == tp->snd_wnd) { /* * If this is the first time we've seen a * FIN from the remote, this is not a * duplicate and it needs to be processed * normally. This happens during a * simultaneous close. */ if ((thflags & TH_FIN) && (TCPS_HAVERCVDFIN(tp->t_state) == 0)) { tp->t_dupacks = 0; break; } /* * If we have outstanding data (other than * a window probe), this is a completely * duplicate ack (ie, window info didn't * change and FIN isn't set), * the ack is the biggest we've * seen and we've seen exactly our rexmt * threshhold of them, assume a packet * has been dropped and retransmit it. * Kludge snd_nxt & the congestion * window so we send only this one * packet. * * We know we're losing at the current * window size so do congestion avoidance * (set ssthresh to half the current window * and pull our congestion window back to * the new ssthresh). * * Dup acks mean that packets have left the * network (they're now cached at the receiver) * so bump cwnd by the amount in the receiver * to keep a constant cwnd packets in the * network. * * When using TCP ECN, notify the peer that * we reduced the cwnd. */ if (!tcp_timer_active(tp, TT_REXMT) || th->th_ack != tp->snd_una) tp->t_dupacks = 0; else if (++tp->t_dupacks > tcprexmtthresh || IN_FASTRECOVERY(tp->t_flags)) { cc_ack_received(tp, th, CC_DUPACK); if ((tp->t_flags & TF_SACK_PERMIT) && IN_FASTRECOVERY(tp->t_flags)) { int awnd; /* * Compute the amount of data in flight first. * We can inject new data into the pipe iff * we have less than 1/2 the original window's * worth of data in flight. */ awnd = (tp->snd_nxt - tp->snd_fack) + tp->sackhint.sack_bytes_rexmit; if (awnd < tp->snd_ssthresh) { tp->snd_cwnd += tp->t_maxseg; if (tp->snd_cwnd > tp->snd_ssthresh) tp->snd_cwnd = tp->snd_ssthresh; } } else tp->snd_cwnd += tp->t_maxseg; #ifdef INSTRUMENT_TCP tcplp_sys_log("TCP DUPACK"); #endif (void) tcp_output(tp); goto drop; } else if (tp->t_dupacks == tcprexmtthresh) { tcp_seq onxt = tp->snd_nxt; /* * If we're doing sack, check to * see if we're already in sack * recovery. If we're not doing sack, * check to see if we're in newreno * recovery. */ if (tp->t_flags & TF_SACK_PERMIT) { if (IN_FASTRECOVERY(tp->t_flags)) { tp->t_dupacks = 0; break; } } else { if (SEQ_LEQ(th->th_ack, tp->snd_recover)) { tp->t_dupacks = 0; break; } } /* Congestion signal before ack. */ cc_cong_signal(tp, th, CC_NDUPACK); cc_ack_received(tp, th, CC_DUPACK); tcp_timer_activate(tp, TT_REXMT, 0); tp->t_rtttime = 0; #ifdef INSTRUMENT_TCP tcplp_sys_log("TCP DUPACK_THRESH"); #endif if (tp->t_flags & TF_SACK_PERMIT) { tp->sack_newdata = tp->snd_nxt; tp->snd_cwnd = tp->t_maxseg; (void) tcp_output(tp); goto drop; } tp->snd_nxt = th->th_ack; tp->snd_cwnd = tp->t_maxseg; (void) tcp_output(tp); /* * samkumar: I added casts to uint64_t below to * fix an OpenThread code scanning alert relating * to integer overflow in multiplication. */ tp->snd_cwnd = tp->snd_ssthresh + ((uint64_t) tp->t_maxseg) * ((uint64_t) (tp->t_dupacks - tp->snd_limited)); #ifdef INSTRUMENT_TCP tcplp_sys_log("TCP SET_cwnd %d", (int) tp->snd_cwnd); #endif if (SEQ_GT(onxt, tp->snd_nxt)) tp->snd_nxt = onxt; goto drop; } else if (V_tcp_do_rfc3042) { /* * Process first and second duplicate * ACKs. Each indicates a segment * leaving the network, creating room * for more. Make sure we can send a * packet on reception of each duplicate * ACK by increasing snd_cwnd by one * segment. Restore the original * snd_cwnd after packet transmission. */ uint64_t oldcwnd; tcp_seq oldsndmax; uint32_t sent; int avail; cc_ack_received(tp, th, CC_DUPACK); oldcwnd = tp->snd_cwnd; oldsndmax = tp->snd_max; #ifdef INSTRUMENT_TCP tcplp_sys_log("TCP LIM_TRANS"); #endif KASSERT(tp->t_dupacks == 1 || tp->t_dupacks == 2, ("%s: dupacks not 1 or 2", __func__)); if (tp->t_dupacks == 1) tp->snd_limited = 0; tp->snd_cwnd = (tp->snd_nxt - tp->snd_una) + (tp->t_dupacks - tp->snd_limited) * tp->t_maxseg; /* * Only call tcp_output when there * is new data available to be sent. * Otherwise we would send pure ACKs. */ /* * samkumar: Replace sbavail(&so->so_snd) with the call to * lbuf_used_space. */ avail = lbuf_used_space(&tp->sendbuf) - (tp->snd_nxt - tp->snd_una); if (avail > 0) (void) tcp_output(tp); sent = tp->snd_max - oldsndmax; if (sent > tp->t_maxseg) { KASSERT((tp->t_dupacks == 2 && tp->snd_limited == 0) || (sent == tp->t_maxseg + 1 && tp->t_flags & TF_SENTFIN), ("%s: sent too much", __func__)); tp->snd_limited = 2; } else if (sent > 0) ++tp->snd_limited; tp->snd_cwnd = oldcwnd; #ifdef INSTRUMENT_TCP tcplp_sys_log("TCP RESET_cwnd %d", (int) tp->snd_cwnd); #endif goto drop; } } else tp->t_dupacks = 0; break; } KASSERT(SEQ_GT(th->th_ack, tp->snd_una), ("%s: th_ack <= snd_una", __func__)); /* * If the congestion window was inflated to account * for the other side's cached packets, retract it. */ if (IN_FASTRECOVERY(tp->t_flags)) { if (SEQ_LT(th->th_ack, tp->snd_recover)) { if (tp->t_flags & TF_SACK_PERMIT) tcp_sack_partialack(tp, th); else tcp_newreno_partial_ack(tp, th); } else cc_post_recovery(tp, th); } tp->t_dupacks = 0; /* * If we reach this point, ACK is not a duplicate, * i.e., it ACKs something we sent. */ if (tp->t_flags & TF_NEEDSYN) { /* * T/TCP: Connection was half-synchronized, and our * SYN has been ACK'd (so connection is now fully * synchronized). Go to non-starred state, * increment snd_una for ACK of SYN, and check if * we can do window scaling. */ tp->t_flags &= ~TF_NEEDSYN; tp->snd_una++; /* Do window scaling? */ if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) == (TF_RCVD_SCALE|TF_REQ_SCALE)) { tp->rcv_scale = tp->request_r_scale; /* Send window already scaled. */ } } process_ACK: acked = BYTES_THIS_ACK(tp, th); tcplp_sys_log("Bytes acked: %d", acked); /* * If we just performed our first retransmit, and the ACK * arrives within our recovery window, then it was a mistake * to do the retransmit in the first place. Recover our * original cwnd and ssthresh, and proceed to transmit where * we left off. */ if (tp->t_rxtshift == 1 && tp->t_flags & TF_PREVVALID && (int)(ticks - tp->t_badrxtwin) < 0) cc_cong_signal(tp, th, CC_RTO_ERR); /* * If we have a timestamp reply, update smoothed * round trip time. If no timestamp is present but * transmit timer is running and timed sequence * number was acked, update smoothed round trip time. * Since we now have an rtt measurement, cancel the * timer backoff (cf., Phil Karn's retransmit alg.). * Recompute the initial retransmit timer. * * Some boxes send broken timestamp replies * during the SYN+ACK phase, ignore * timestamps of 0 or we could calculate a * huge RTT and blow up the retransmit timer. */ if ((to.to_flags & TOF_TS) != 0 && to.to_tsecr) { uint32_t t; t = tcp_ts_getticks() - to.to_tsecr; if (!tp->t_rttlow || tp->t_rttlow > t) tp->t_rttlow = t; tcp_xmit_timer(tp, TCP_TS_TO_TICKS(t) + 1); } else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq)) { if (!tp->t_rttlow || tp->t_rttlow > ticks - tp->t_rtttime) tp->t_rttlow = ticks - tp->t_rtttime; tcp_xmit_timer(tp, ticks - tp->t_rtttime); } /* * If all outstanding data is acked, stop retransmit * timer and remember to restart (more output or persist). * If there is more data to be acked, restart retransmit * timer, using current (possibly backed-off) value. */ if (th->th_ack == tp->snd_max) { tcp_timer_activate(tp, TT_REXMT, 0); needoutput = 1; } else if (!tcp_timer_active(tp, TT_PERSIST)) { tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur); } /* * If no data (only SYN) was ACK'd, * skip rest of ACK processing. */ if (acked == 0) goto step6; /* * Let the congestion control algorithm update congestion * control related information. This typically means increasing * the congestion window. */ cc_ack_received(tp, th, CC_ACK); /* * samkumar: I replaced the calls to sbavail(&so->so_snd) with new * calls to lbuf_used_space, and then I modified the code to actually * remove code from the send buffer, formerly done via * sbcut_locked(&so->so_send, (int)sbavail(&so->so_snd)) in the if case * and sbcut_locked(&so->so_snd, acked) in the else case, to use the * data structures for TCPlp's data buffering. */ if (acked > lbuf_used_space(&tp->sendbuf)) { uint32_t poppedbytes; uint32_t usedspace = lbuf_used_space(&tp->sendbuf); tp->snd_wnd -= usedspace; poppedbytes = lbuf_pop(&tp->sendbuf, usedspace, &sig->links_popped); KASSERT(poppedbytes == usedspace, ("Could not fully empty send buffer")); sig->bytes_acked += poppedbytes; ourfinisacked = 1; } else { uint32_t poppedbytes = lbuf_pop(&tp->sendbuf, acked, &sig->links_popped); KASSERT(poppedbytes == acked, ("Could not remove acked bytes from send buffer")); sig->bytes_acked += poppedbytes; tp->snd_wnd -= acked; ourfinisacked = 0; } /* NB: sowwakeup_locked() does an implicit unlock. */ /* * samkumar: There used to be a call to sowwakeup(so); here, * which wakes up any threads waiting for the socket to * become ready for writing. TCPlp handles its send buffer * differently so we do not need to replace this call with * specialized code to handle this. */ /* Detect una wraparound. */ if (!IN_RECOVERY(tp->t_flags) && SEQ_GT(tp->snd_una, tp->snd_recover) && SEQ_LEQ(th->th_ack, tp->snd_recover)) tp->snd_recover = th->th_ack - 1; /* XXXLAS: Can this be moved up into cc_post_recovery? */ if (IN_RECOVERY(tp->t_flags) && SEQ_GEQ(th->th_ack, tp->snd_recover)) { EXIT_RECOVERY(tp->t_flags); } tp->snd_una = th->th_ack; if (tp->t_flags & TF_SACK_PERMIT) { if (SEQ_GT(tp->snd_una, tp->snd_recover)) tp->snd_recover = tp->snd_una; } if (SEQ_LT(tp->snd_nxt, tp->snd_una)) tp->snd_nxt = tp->snd_una; switch (tp->t_state) { /* * In FIN_WAIT_1 STATE in addition to the processing * for the ESTABLISHED state if our FIN is now acknowledged * then enter FIN_WAIT_2. */ case TCPS_FIN_WAIT_1: if (ourfinisacked) { /* * If we can't receive any more * data, then closing user can proceed. * Starting the timer is contrary to the * specification, but if we don't get a FIN * we'll hang forever. * * XXXjl: * we should release the tp also, and use a * compressed state. */ /* * samkumar: I replaced a check for the SBS_CANTRCVMORE flag * in so->so_rcv.sb_state with a call to tcpiscantrcv. */ if (tpiscantrcv(tp)) { /* samkumar: Removed a call to soisdisconnected(so). */ tcp_timer_activate(tp, TT_2MSL, (tcp_fast_finwait2_recycle ? tcp_finwait2_timeout : TP_MAXIDLE(tp))); } tcp_state_change(tp, TCPS_FIN_WAIT_2); } break; /* * In CLOSING STATE in addition to the processing for * the ESTABLISHED state if the ACK acknowledges our FIN * then enter the TIME-WAIT state, otherwise ignore * the segment. */ case TCPS_CLOSING: if (ourfinisacked) { /* * samkumar: I added the line below. We need to avoid sending * an ACK in the TIME-WAIT state, since we don't want to * ACK ACKs. This edge case appears because TCPlp, unlike the * original FreeBSD code, uses tcpcbs for connections in the * TIME-WAIT state (FreeBSD uses a different, smaller * structure). */ tp->t_flags &= ~TF_ACKNOW; tcp_twstart(tp); return; } break; /* * In LAST_ACK, we may still be waiting for data to drain * and/or to be acked, as well as for the ack of our FIN. * If our FIN is now acknowledged, delete the TCB, * enter the closed state and return. */ case TCPS_LAST_ACK: if (ourfinisacked) { tp = tcp_close(tp); tcplp_sys_connection_lost(tp, CONN_LOST_NORMAL); goto drop; } break; } } step6: /* * Update window information. * Don't look at window if no ACK: TAC's send garbage on first SYN. */ if ((thflags & TH_ACK) && (SEQ_LT(tp->snd_wl1, th->th_seq) || (tp->snd_wl1 == th->th_seq && (SEQ_LT(tp->snd_wl2, th->th_ack) || (tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd))))) { /* keep track of pure window updates */ /* * samkumar: There used to be an if statement here that would check if * this is a "pure" window update (tlen == 0 && * tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd) and keep * statistics for how often that happens. */ tp->snd_wnd = tiwin; tp->snd_wl1 = th->th_seq; tp->snd_wl2 = th->th_ack; if (tp->snd_wnd > tp->max_sndwnd) tp->max_sndwnd = tp->snd_wnd; needoutput = 1; } /* * Process segments with URG. */ /* * samkumar: TCPlp does not support the urgent pointer, so we omit all * urgent-pointer-related processing and buffering. The code below is the * code that was in the "else" case that handles no valid urgent data in * the received packet. */ { /* * If no out of band data is expected, * pull receive urgent pointer along * with the receive window. */ if (SEQ_GT(tp->rcv_nxt, tp->rcv_up)) tp->rcv_up = tp->rcv_nxt; } /* * Process the segment text, merging it into the TCP sequencing queue, * and arranging for acknowledgment of receipt if necessary. * This process logically involves adjusting tp->rcv_wnd as data * is presented to the user (this happens in tcp_usrreq.c, * case PRU_RCVD). If a FIN has already been received on this * connection then we just ignore the text. */ tfo_syn = ((tp->t_state == TCPS_SYN_RECEIVED) && IS_FASTOPEN(tp->t_flags)); if ((tlen || (thflags & TH_FIN) || tfo_syn) && TCPS_HAVERCVDFIN(tp->t_state) == 0) { tcp_seq save_start = th->th_seq; /* * samkumar: I removed a call to m_adj(m, drop_hdrlen), which intends * to drop data from the mbuf so it can be chained into the receive * header. This is not necessary for TCPlp because we copy the data * anyway; we just add the offset when copying data into the receive * buffer. */ /* * Insert segment which includes th into TCP reassembly queue * with control block tp. Set thflags to whether reassembly now * includes a segment with FIN. This handles the common case * inline (segment is the next to be received on an established * connection, and the queue is empty), avoiding linkage into * and removal from the queue and repetition of various * conversions. * Set DELACK for segments received in order, but ack * immediately when segments are out of order (so * fast retransmit can work). */ /* * samkumar: I replaced LIST_EMPTY(&tp->t_segq) with the calls to * tpiscantrcv and bmp_isempty on the second line below. */ if (th->th_seq == tp->rcv_nxt && (tpiscantrcv(tp) || bmp_isempty(tp->reassbmp, REASSBMP_SIZE(tp))) && (TCPS_HAVEESTABLISHED(tp->t_state) || tfo_syn)) { if (DELAY_ACK(tp, tlen) || tfo_syn) tp->t_flags |= TF_DELACK; else tp->t_flags |= TF_ACKNOW; tp->rcv_nxt += tlen; thflags = th->th_flags & TH_FIN; /* * samkumar: I replaced the code that used to be here (which would * free the mbuf with m_freem(m) if the SBS_CANTRCVMORE flag is set * on so->so_rcv.sb_state, and otherwise call * sbappendstream_locked(&so->so_rcv, m, 0);). */ if (!tpiscantrcv(tp)) { cbuf_write(&tp->recvbuf, msg, otMessageGetOffset(msg) + drop_hdrlen, tlen, cbuf_copy_from_message); if (tlen > 0) { sig->recvbuf_added = true; } } else if (tlen > 0) { /* * samkumar: We already know tlen != 0, so if we got here, then * it means that we got data after we called SHUT_RD, or after * receiving a FIN. I'm going to drop the connection in this * case. I think FreeBSD might have just dropped the packet * silently, but Linux handles it this way; this seems to be * the right approach to me. */ tcp_drop(tp, ECONNABORTED); goto drop; } /* NB: sorwakeup_locked() does an implicit unlock. */ /* * samkumar: There used to be a call to sorwakeup_locked(so); here, * which wakes up any threads waiting for the socket to become * become ready for reading. TCPlp handles its buffering * differently so we do not need to replace this call with * specialized code to handle this. */ } else if (tpiscantrcv(tp)) { /* * samkumar: We will reach this point if we get out-of-order data * on a socket which was shut down with SHUT_RD, or where we * already received a FIN. My response here is to drop the segment * and send an RST. */ tcp_drop(tp, ECONNABORTED); goto drop; } else { /* * XXX: Due to the header drop above "th" is * theoretically invalid by now. Fortunately * m_adj() doesn't actually frees any mbufs * when trimming from the head. */ thflags = tcp_reass(tp, th, &tlen, msg, otMessageGetOffset(msg) + drop_hdrlen, sig); tp->t_flags |= TF_ACKNOW; } // Only place tlen is used after the call to tcp_reass is below if (tlen > 0 && (tp->t_flags & TF_SACK_PERMIT)) tcp_update_sack_list(tp, save_start, save_start + tlen); /* * samkumar: This is not me commenting things out; this was already * commented out in the FreeBSD code. */ #if 0 /* * Note the amount of data that peer has sent into * our window, in order to estimate the sender's * buffer size. * XXX: Unused. */ if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt)) len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt); else len = so->so_rcv.sb_hiwat; #endif } else { thflags &= ~TH_FIN; } /* * If FIN is received ACK the FIN and let the user know * that the connection is closing. */ if (thflags & TH_FIN) { tcplp_sys_log("FIN Processing start"); if (TCPS_HAVERCVDFIN(tp->t_state) == 0) { /* samkumar: replace socantrcvmore with tpcantrcvmore */ tpcantrcvmore(tp); /* * If connection is half-synchronized * (ie NEEDSYN flag on) then delay ACK, * so it may be piggybacked when SYN is sent. * Otherwise, since we received a FIN then no * more input can be expected, send ACK now. */ if (tp->t_flags & TF_NEEDSYN) tp->t_flags |= TF_DELACK; else tp->t_flags |= TF_ACKNOW; tp->rcv_nxt++; } /* * samkumar: This -2 state is added by me, so that we do not consider * any more FINs in reassembly. */ if (tp->reass_fin_index != -2) { sig->rcvd_fin = true; tp->reass_fin_index = -2; } switch (tp->t_state) { /* * In SYN_RECEIVED and ESTABLISHED STATES * enter the CLOSE_WAIT state. */ case TCPS_SYN_RECEIVED: tp->t_starttime = ticks; /* FALLTHROUGH */ case TCPS_ESTABLISHED: tcp_state_change(tp, TCPS_CLOSE_WAIT); break; /* * If still in FIN_WAIT_1 STATE FIN has not been acked so * enter the CLOSING state. */ case TCPS_FIN_WAIT_1: tcp_state_change(tp, TCPS_CLOSING); break; /* * In FIN_WAIT_2 state enter the TIME_WAIT state, * starting the time-wait timer, turning off the other * standard timers. */ case TCPS_FIN_WAIT_2: tcp_twstart(tp); return; } } /* * samkumar: Remove code for synchronization and debugging, here and in * the labels below. I also removed the line to free the mbuf if it hasn't * been freed already (the line was "m_freem(m)"). */ /* * Return any desired output. */ if (needoutput || (tp->t_flags & TF_ACKNOW)) (void) tcp_output(tp); check_delack: if (tp->t_flags & TF_DELACK) { tp->t_flags &= ~TF_DELACK; tcp_timer_activate(tp, TT_DELACK, tcp_delacktime); } return; dropafterack: /* * Generate an ACK dropping incoming segment if it occupies * sequence space, where the ACK reflects our state. * * We can now skip the test for the RST flag since all * paths to this code happen after packets containing * RST have been dropped. * * In the SYN-RECEIVED state, don't send an ACK unless the * segment we received passes the SYN-RECEIVED ACK test. * If it fails send a RST. This breaks the loop in the * "LAND" DoS attack, and also prevents an ACK storm * between two listening ports that have been sent forged * SYN segments, each with the source address of the other. */ if (tp->t_state == TCPS_SYN_RECEIVED && (thflags & TH_ACK) && (SEQ_GT(tp->snd_una, th->th_ack) || SEQ_GT(th->th_ack, tp->snd_max)) ) { rstreason = BANDLIM_RST_OPENPORT; goto dropwithreset; } tp->t_flags |= TF_ACKNOW; (void) tcp_output(tp); return; dropwithreset: if (tp != NULL) { tcp_dropwithreset(ip6, th, tp, instance, tlen, rstreason); } else tcp_dropwithreset(ip6, th, NULL, instance, tlen, rstreason); return; drop: return; } /* * Parse TCP options and place in tcpopt. */ static void tcp_dooptions(struct tcpopt *to, uint8_t *cp, int cnt, int flags) { int opt, optlen; to->to_flags = 0; for (; cnt > 0; cnt -= optlen, cp += optlen) { opt = cp[0]; if (opt == TCPOPT_EOL) break; if (opt == TCPOPT_NOP) optlen = 1; else { if (cnt < 2) break; optlen = cp[1]; if (optlen < 2 || optlen > cnt) break; } switch (opt) { case TCPOPT_MAXSEG: if (optlen != TCPOLEN_MAXSEG) continue; if (!(flags & TO_SYN)) continue; to->to_flags |= TOF_MSS; bcopy((char *)cp + 2, (char *)&to->to_mss, sizeof(to->to_mss)); to->to_mss = ntohs(to->to_mss); break; case TCPOPT_WINDOW: if (optlen != TCPOLEN_WINDOW) continue; if (!(flags & TO_SYN)) continue; to->to_flags |= TOF_SCALE; to->to_wscale = min(cp[2], TCP_MAX_WINSHIFT); break; case TCPOPT_TIMESTAMP: if (optlen != TCPOLEN_TIMESTAMP) continue; to->to_flags |= TOF_TS; bcopy((char *)cp + 2, (char *)&to->to_tsval, sizeof(to->to_tsval)); to->to_tsval = ntohl(to->to_tsval); bcopy((char *)cp + 6, (char *)&to->to_tsecr, sizeof(to->to_tsecr)); to->to_tsecr = ntohl(to->to_tsecr); break; #ifdef TCP_SIGNATURE /* * XXX In order to reply to a host which has set the * TCP_SIGNATURE option in its initial SYN, we have to * record the fact that the option was observed here * for the syncache code to perform the correct response. */ case TCPOPT_SIGNATURE: if (optlen != TCPOLEN_SIGNATURE) continue; to->to_flags |= TOF_SIGNATURE; to->to_signature = cp + 2; break; #endif case TCPOPT_SACK_PERMITTED: if (optlen != TCPOLEN_SACK_PERMITTED) continue; if (!(flags & TO_SYN)) continue; if (!V_tcp_do_sack) continue; to->to_flags |= TOF_SACKPERM; break; case TCPOPT_SACK: if (optlen <= 2 || (optlen - 2) % TCPOLEN_SACK != 0) continue; if (flags & TO_SYN) continue; to->to_flags |= TOF_SACK; to->to_nsacks = (optlen - 2) / TCPOLEN_SACK; to->to_sacks = cp + 2; break; case TCPOPT_FAST_OPEN: /* * Cookie length validation is performed by the * server side cookie checking code or the client * side cookie cache update code. */ if (!(flags & TO_SYN)) continue; if (!V_tcp_fastopen_client_enable && !V_tcp_fastopen_server_enable) continue; to->to_flags |= TOF_FASTOPEN; to->to_tfo_len = optlen - 2; to->to_tfo_cookie = to->to_tfo_len ? cp + 2 : NULL; break; default: continue; } } } /* * Collect new round-trip time estimate * and update averages and current timeout. */ static void tcp_xmit_timer(struct tcpcb *tp, int rtt) { int delta; tp->t_rttupdated++; if (tp->t_srtt != 0) { /* * srtt is stored as fixed point with 5 bits after the * binary point (i.e., scaled by 8). The following magic * is equivalent to the smoothing algorithm in rfc793 with * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed * point). Adjust rtt to origin 0. */ delta = ((rtt - 1) << TCP_DELTA_SHIFT) - (tp->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT)); if ((tp->t_srtt += delta) <= 0) tp->t_srtt = 1; /* * We accumulate a smoothed rtt variance (actually, a * smoothed mean difference), then set the retransmit * timer to smoothed rtt + 4 times the smoothed variance. * rttvar is stored as fixed point with 4 bits after the * binary point (scaled by 16). The following is * equivalent to rfc793 smoothing with an alpha of .75 * (rttvar = rttvar*3/4 + |delta| / 4). This replaces * rfc793's wired-in beta. */ if (delta < 0) delta = -delta; delta -= tp->t_rttvar >> (TCP_RTTVAR_SHIFT - TCP_DELTA_SHIFT); if ((tp->t_rttvar += delta) <= 0) tp->t_rttvar = 1; if (tp->t_rttbest > tp->t_srtt + tp->t_rttvar) tp->t_rttbest = tp->t_srtt + tp->t_rttvar; } else { /* * No rtt measurement yet - use the unsmoothed rtt. * Set the variance to half the rtt (so our first * retransmit happens at 3*rtt). */ tp->t_srtt = rtt << TCP_RTT_SHIFT; tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1); tp->t_rttbest = tp->t_srtt + tp->t_rttvar; } tp->t_rtttime = 0; tp->t_rxtshift = 0; /* * the retransmit should happen at rtt + 4 * rttvar. * Because of the way we do the smoothing, srtt and rttvar * will each average +1/2 tick of bias. When we compute * the retransmit timer, we want 1/2 tick of rounding and * 1 extra tick because of +-1/2 tick uncertainty in the * firing of the timer. The bias will give us exactly the * 1.5 tick we need. But, because the bias is * statistical, we have to test that we don't drop below * the minimum feasible timer (which is 2 ticks). */ TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp), max(tp->t_rttmin, rtt + 2), TCPTV_REXMTMAX); #ifdef INSTRUMENT_TCP tcplp_sys_log("TCP timer %u %d %d %d", (unsigned int) tcplp_sys_get_millis(), rtt, (int) tp->t_srtt, (int) tp->t_rttvar); #endif /* * We received an ack for a packet that wasn't retransmitted; * it is probably safe to discard any error indications we've * received recently. This isn't quite right, but close enough * for now (a route might have failed after we sent a segment, * and the return path might not be symmetrical). */ tp->t_softerror = 0; } /* * samkumar: Taken from netinet6/in6.c. * * This function is supposed to check whether the provided address is an * IPv6 address of this host. This function, however, is used only as a hint, * as the MSS is clamped at V_tcp_v6mssdflt for connections to non-local * addresses. It is difficult for us to actually determine if the address * belongs to us, so we are conservative and only return 1 (true) if it is * obviously so---we keep the part of the function that checks for loopback or * link local and remove the rest of the code that checks for the addresses * assigned to interfaces. In cases where we return 0 but should have returned * 1, we may conservatively clamp the MTU, but that should be OK for TCPlp. * In fact, the constants are set such that we'll get the right answer whether * we clamp or not, so this shouldn't really matter at all. */ int in6_localaddr(struct in6_addr *in6) { if (IN6_IS_ADDR_LOOPBACK(in6) || IN6_IS_ADDR_LINKLOCAL(in6)) return 1; return (0); } /* * Determine a reasonable value for maxseg size. * If the route is known, check route for mtu. * If none, use an mss that can be handled on the outgoing interface * without forcing IP to fragment. If no route is found, route has no mtu, * or the destination isn't local, use a default, hopefully conservative * size (usually 512 or the default IP max size, but no more than the mtu * of the interface), as we can't discover anything about intervening * gateways or networks. We also initialize the congestion/slow start * window to be a single segment if the destination isn't local. * While looking at the routing entry, we also initialize other path-dependent * parameters from pre-set or cached values in the routing entry. * * Also take into account the space needed for options that we * send regularly. Make maxseg shorter by that amount to assure * that we can send maxseg amount of data even when the options * are present. Store the upper limit of the length of options plus * data in maxopd. * * NOTE that this routine is only called when we process an incoming * segment, or an ICMP need fragmentation datagram. Outgoing SYN/ACK MSS * settings are handled in tcp_mssopt(). */ /* * samkumar: Using struct tcpcb instead of the inpcb. */ void tcp_mss_update(struct tcpcb *tp, int offer, int mtuoffer, struct hc_metrics_lite *metricptr, struct tcp_ifcap *cap) { /* * samkumar: I removed all IPv4-specific logic and cases, including logic * to check for IPv4 vs. IPv6, as well as all locking and debugging code. */ int mss = 0; uint64_t maxmtu = 0; struct hc_metrics_lite metrics; int origoffer; size_t min_protoh = IP6HDR_SIZE + sizeof (struct tcphdr); if (mtuoffer != -1) { KASSERT(offer == -1, ("%s: conflict", __func__)); offer = mtuoffer - min_protoh; } origoffer = offer; maxmtu = tcp_maxmtu6(tp, cap); tp->t_maxopd = tp->t_maxseg = V_tcp_v6mssdflt; /* * No route to sender, stay with default mss and return. */ if (maxmtu == 0) { /* * In case we return early we need to initialize metrics * to a defined state as tcp_hc_get() would do for us * if there was no cache hit. */ if (metricptr != NULL) bzero(metricptr, sizeof(struct hc_metrics_lite)); return; } /* What have we got? */ switch (offer) { case 0: /* * Offer == 0 means that there was no MSS on the SYN * segment, in this case we use tcp_mssdflt as * already assigned to t_maxopd above. */ offer = tp->t_maxopd; break; case -1: /* * Offer == -1 means that we didn't receive SYN yet. */ /* FALLTHROUGH */ default: /* * Prevent DoS attack with too small MSS. Round up * to at least minmss. */ offer = max(offer, V_tcp_minmss); } /* * rmx information is now retrieved from tcp_hostcache. */ tcp_hc_get(tp, &metrics); if (metricptr != NULL) bcopy(&metrics, metricptr, sizeof(struct hc_metrics_lite)); /* * If there's a discovered mtu in tcp hostcache, use it. * Else, use the link mtu. */ if (metrics.rmx_mtu) mss = min(metrics.rmx_mtu, maxmtu) - min_protoh; else { mss = maxmtu - min_protoh; if (!V_path_mtu_discovery && !in6_localaddr(&tp->faddr)) mss = min(mss, V_tcp_v6mssdflt); /* * XXX - The above conditional (mss = maxmtu - min_protoh) * probably violates the TCP spec. * The problem is that, since we don't know the * other end's MSS, we are supposed to use a conservative * default. But, if we do that, then MTU discovery will * never actually take place, because the conservative * default is much less than the MTUs typically seen * on the Internet today. For the moment, we'll sweep * this under the carpet. * * The conservative default might not actually be a problem * if the only case this occurs is when sending an initial * SYN with options and data to a host we've never talked * to before. Then, they will reply with an MSS value which * will get recorded and the new parameters should get * recomputed. For Further Study. */ } mss = min(mss, offer); /* * Sanity check: make sure that maxopd will be large * enough to allow some data on segments even if the * all the option space is used (40bytes). Otherwise * funny things may happen in tcp_output. */ /* * samkumar: When I was experimenting with different MSS values, I had * changed this to "mss = max(mss, TCP_MAXOLEN + 1);" but I am changing it * back for the version that will be merged into OpenThread. */ mss = max(mss, 64); /* * maxopd stores the maximum length of data AND options * in a segment; maxseg is the amount of data in a normal * segment. We need to store this value (maxopd) apart * from maxseg, because now every segment carries options * and thus we normally have somewhat less data in segments. */ tp->t_maxopd = mss; /* * origoffer==-1 indicates that no segments were received yet. * In this case we just guess. */ if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP && (origoffer == -1 || (tp->t_flags & TF_RCVD_TSTMP) == TF_RCVD_TSTMP)) mss -= TCPOLEN_TSTAMP_APPA; tp->t_maxseg = mss; } void tcp_mss(struct tcpcb *tp, int offer) { struct hc_metrics_lite metrics; struct tcp_ifcap cap; KASSERT(tp != NULL, ("%s: tp == NULL", __func__)); bzero(&cap, sizeof(cap)); tcp_mss_update(tp, offer, -1, &metrics, &cap); /* * samkumar: There used to be code below that might modify the MSS, but I * removed all of it (see the comments below for the reason). It used to * read tp->t_maxseg into the local variable mss, modify mss, and then * reassign tp->t_maxseg to mss. I've kept the assignments, commented out, * for clarity. */ //mss = tp->t_maxseg; /* * If there's a pipesize, change the socket buffer to that size, * don't change if sb_hiwat is different than default (then it * has been changed on purpose with setsockopt). * Make the socket buffers an integral number of mss units; * if the mss is larger than the socket buffer, decrease the mss. */ /* * samkumar: There used to be code here would would limit the MSS to at * most the size of the send buffer, and then round up the send buffer to * a multiple of the MSS using * "sbreserve_locked(&so->so_snd, bufsize, so, NULL);". With TCPlp, we do * not do this, because the linked buffer used at the send buffer doesn't * have a real limit. Had we used a circular buffer, then limiting the MSS * to the buffer size would have made sense, but we still would not be able * to resize the send buffer because it is not allocated by TCPlp. */ /* * samkumar: See the comment above about me removing code that modifies * the MSS, making this assignment and the one above both unnecessary. */ //tp->t_maxseg = mss; /* * samkumar: There used to be code here that would round up the receive * buffer size to a multiple of the MSS, assuming that the receive buffer * size is bigger than the MSS. The new buffer size is set using * "sbreserve_locked(&so->so_rcv, bufsize, so, NULL);". In TCPlp, the * buffer is not allocated by TCPlp so I removed the code for this. */ /* * samkumar: There used to be code here to handle TCP Segmentation * Offloading (TSO); I removed it becuase we don't support that in TCPlp. */ } /* * Determine the MSS option to send on an outgoing SYN. */ /* * samkumar: In the signature, changed "struct in_conninfo *inc" to * "struct tcpcb* tp". */ int tcp_mssopt(struct tcpcb* tp) { /* * samkumar: I removed all processing code specific to IPv4, or to decide * between IPv4 and IPv6. This is OK because TCPlp assumes IPv6. */ int mss = 0; uint64_t maxmtu = 0; uint64_t thcmtu = 0; size_t min_protoh; KASSERT(tp != NULL, ("tcp_mssopt with NULL tcpcb pointer")); mss = V_tcp_v6mssdflt; maxmtu = tcp_maxmtu6(tp, NULL); min_protoh = IP6HDR_SIZE + sizeof(struct tcphdr); thcmtu = tcp_hc_getmtu(tp); /* IPv4 and IPv6 */ if (maxmtu && thcmtu) mss = min(maxmtu, thcmtu) - min_protoh; else if (maxmtu || thcmtu) mss = max(maxmtu, thcmtu) - min_protoh; return (mss); } /* * On a partial ack arrives, force the retransmission of the * next unacknowledged segment. Do not clear tp->t_dupacks. * By setting snd_nxt to ti_ack, this forces retransmission timer to * be started again. */ static void tcp_newreno_partial_ack(struct tcpcb *tp, struct tcphdr *th) { tcp_seq onxt = tp->snd_nxt; uint64_t ocwnd = tp->snd_cwnd; tcp_timer_activate(tp, TT_REXMT, 0); tp->t_rtttime = 0; tp->snd_nxt = th->th_ack; /* * Set snd_cwnd to one segment beyond acknowledged offset. * (tp->snd_una has not yet been updated when this function is called.) */ tp->snd_cwnd = tp->t_maxseg + BYTES_THIS_ACK(tp, th); tp->t_flags |= TF_ACKNOW; #ifdef INSTRUMENT_TCP tcplp_sys_log("TCP Partial_ACK"); #endif (void) tcp_output(tp); tp->snd_cwnd = ocwnd; if (SEQ_GT(onxt, tp->snd_nxt)) tp->snd_nxt = onxt; /* * Partial window deflation. Relies on fact that tp->snd_una * not updated yet. */ if (tp->snd_cwnd > BYTES_THIS_ACK(tp, th)) tp->snd_cwnd -= BYTES_THIS_ACK(tp, th); else tp->snd_cwnd = 0; tp->snd_cwnd += tp->t_maxseg; #ifdef INSTRUMENT_TCP tcplp_sys_log("TCP Partial_ACK_final %d", (int) tp->snd_cwnd); #endif }