]> git.saurik.com Git - apple/xnu.git/blobdiff - bsd/netinet/tcp_output.c
xnu-6153.141.1.tar.gz
[apple/xnu.git] / bsd / netinet / tcp_output.c
index 88ced34e95502914be7bce142bd80a5541377c1b..7c1988f1f9467987fc6e330ef940e511f3ae7205 100644 (file)
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2000-2017 Apple Inc. All rights reserved.
+ * Copyright (c) 2000-2019 Apple Inc. All rights reserved.
  *
  * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
  *
 #if TCPDEBUG
 #include <netinet/tcp_debug.h>
 #endif
+#include <netinet/tcp_log.h>
 #include <sys/kdebug.h>
 #include <mach/sdt.h>
 
@@ -166,14 +167,14 @@ sysctl_change_ecn_setting SYSCTL_HANDLER_ARGS
        err = sysctl_io_number(req, tcp_ecn_outbound, sizeof(int32_t),
            &i, &changed);
        if (err != 0 || req->newptr == USER_ADDR_NULL)
-               return(err);
+               return err;
 
        if (changed) {
                if ((tcp_ecn_outbound == 0 || tcp_ecn_outbound == 1) &&
                    (i == 0 || i == 1)) {
                        tcp_ecn_outbound = i;
                        SYSCTL_SKMEM_UPDATE_FIELD(tcp.ecn_initiate_out, tcp_ecn_outbound);
-                       return(err);
+                       return err;
                }
                if (tcp_ecn_outbound == 2 && (i == 0 || i == 1)) {
                        /*
@@ -215,7 +216,7 @@ sysctl_change_ecn_setting SYSCTL_HANDLER_ARGS
                tcp_ecn_inbound = i;
                SYSCTL_SKMEM_UPDATE_FIELD(tcp.ecn_negotiate_in, tcp_ecn_inbound);
        }
-       return (err);
+       return err;
 }
 
 int     tcp_ecn_outbound = 2;
@@ -310,18 +311,15 @@ static int32_t tcp_tfo_check(struct tcpcb *tp, int32_t len)
        if (tp->t_flags & TF_NOOPT)
                goto fallback;
 
-       if ((so->so_flags1 & SOF1_DATA_AUTHENTICATED) &&
-           !(tp->t_flagsext & TF_FASTOPEN_HEUR))
-               return (len);
-
-       if (!tcp_heuristic_do_tfo(tp)) {
+       if (!(tp->t_flagsext & TF_FASTOPEN_FORCE_ENABLE) &&
+           !tcp_heuristic_do_tfo(tp)) {
                tp->t_tfo_stats |= TFO_S_HEURISTICS_DISABLE;
                tcpstat.tcps_tfo_heuristics_disable++;
                goto fallback;
        }
 
        if (so->so_flags1 & SOF1_DATA_AUTHENTICATED)
-               return (len);
+               return len;
 
        optlen += TCPOLEN_MAXSEG;
 
@@ -330,7 +328,8 @@ static int32_t tcp_tfo_check(struct tcpcb *tp, int32_t len)
 
 #if MPTCP
        if ((so->so_flags & SOF_MP_SUBFLOW) && mptcp_enable &&
-           tp->t_rxtshift <= mptcp_mpcap_retries)
+           (tp->t_rxtshift <= mptcp_mpcap_retries ||
+           (tptomptp(tp)->mpt_mpte->mpte_flags & MPTE_FORCE_ENABLE)))
                optlen += sizeof(struct mptcp_mpcapable_opt_common) + sizeof(mptcp_key_t);
 #endif /* MPTCP */
 
@@ -349,7 +348,7 @@ static int32_t tcp_tfo_check(struct tcpcb *tp, int32_t len)
        cookie_len = tcp_cache_get_cookie_len(tp);
        if (cookie_len == 0)
                /* No cookie, so we request one */
-               return (0);
+               return 0;
 
        /* There is not enough space for the cookie, so we cannot do TFO */
        if (MAX_TCPOPTLEN - optlen < cookie_len)
@@ -360,11 +359,11 @@ static int32_t tcp_tfo_check(struct tcpcb *tp, int32_t len)
                goto fallback;
 
        /* Ok, everything looks good. We can go on and do TFO */
-       return (len);
+       return len;
 
 fallback:
-       tp->t_flagsext &= ~TF_FASTOPEN;
-       return (0);
+       tcp_disable_tfo(tp);
+       return 0;
 }
 
 /* Returns the number of bytes written to the TCP option-space */
@@ -377,7 +376,7 @@ tcp_tfo_write_cookie_rep(struct tcpcb *tp, unsigned optlen, u_char *opt)
 
        if ((MAX_TCPOPTLEN - optlen) <
            (TCPOLEN_FASTOPEN_REQ + TFO_COOKIE_LEN_DEFAULT))
-               return (ret);
+               return ret;
 
        tcp_tfo_gen_cookie(tp->t_inpcb, out, sizeof(out));
 
@@ -391,7 +390,7 @@ tcp_tfo_write_cookie_rep(struct tcpcb *tp, unsigned optlen, u_char *opt)
        tp->t_tfo_stats |= TFO_S_COOKIE_SENT;
        tcpstat.tcps_tfo_cookie_sent++;
 
-       return (ret);
+       return ret;
 }
 
 static unsigned
@@ -411,7 +410,7 @@ tcp_tfo_write_cookie(struct tcpcb *tp, unsigned optlen, int32_t len,
                        tcpstat.tcps_tfo_syn_data_sent++;
                }
 
-               return (0);
+               return 0;
        }
 
        bp = opt + optlen;
@@ -446,15 +445,15 @@ tcp_tfo_write_cookie(struct tcpcb *tp, unsigned optlen, int32_t len,
                }
        }
 
-       return (ret);
+       return ret;
 }
 
 static inline bool
 tcp_send_ecn_flags_on_syn(struct tcpcb *tp, struct socket *so)
 {
-       return(!((tp->ecn_flags & TE_SETUPSENT) ||
+       return !((tp->ecn_flags & TE_SETUPSENT ||
            (so->so_flags & SOF_MP_SUBFLOW) ||
-           (tp->t_flagsext & TF_FASTOPEN)));
+           (tfo_enabled(tp))));
 }
 
 void
@@ -642,7 +641,7 @@ tcp_output(struct tcpcb *tp)
                 * the subflow socket stays around until deleted.
                 * No packets such as FINs must be sent after RST.
                 */
-               return (0);
+               return 0;
        }
 #endif /* MPTCP */
 
@@ -708,18 +707,18 @@ again:
 
                        if (tp->t_state >= TCPS_CLOSE_WAIT) {
                                tcp_drop(tp, EADDRNOTAVAIL);
-                               return(EADDRNOTAVAIL);
+                               return EADDRNOTAVAIL;
                        }
 
-                       /* Set retransmit  timer if it wasn't set,
+                       /*
+                        * Set retransmit  timer if it wasn't set,
                         * reset Persist timer and shift register as the
                         * advertised peer window may not be valid anymore
                         */
-
-                       if (!tp->t_timer[TCPT_REXMT]) {
+                       if (tp->t_timer[TCPT_REXMT] == 0) {
                                tp->t_timer[TCPT_REXMT] =
                                    OFFSET_FROM_START(tp, tp->t_rxtcur);
-                               if (tp->t_timer[TCPT_PERSIST]) {
+                               if (tp->t_timer[TCPT_PERSIST] != 0) {
                                        tp->t_timer[TCPT_PERSIST] = 0;
                                        tp->t_persist_stop = 0;
                                        TCP_RESET_REXMT_STATE(tp);
@@ -733,10 +732,10 @@ again:
                        /* drop connection if source address isn't available */
                        if (so->so_flags & SOF_NOADDRAVAIL) {
                                tcp_drop(tp, EADDRNOTAVAIL);
-                               return(EADDRNOTAVAIL);
+                               return EADDRNOTAVAIL;
                        } else {
                                tcp_check_timer_state(tp);
-                               return(0); /* silently ignore, keep data in socket: address may be back */
+                               return 0; /* silently ignore, keep data in socket: address may be back */
                        }
                }
                if (ia != NULL)
@@ -766,7 +765,7 @@ again:
                 *         has been disabled)
                 */
 
-               if (!path_mtu_discovery || ((rt != NULL) &&
+               if (!path_mtu_discovery || ((rt != NULL) &&
                    (!(rt->rt_flags & RTF_UP) ||
                    (rt->rt_rmx.rmx_locks & RTV_MTU))))
                        tp->t_flags &= ~TF_PMTUD;
@@ -979,39 +978,47 @@ after_sack_rexmit:
         * know that foreign host supports TAO, suppress sending segment.
         */
        if ((flags & TH_SYN) && SEQ_GT(tp->snd_nxt, tp->snd_una)) {
-               if (tp->t_state != TCPS_SYN_RECEIVED || tfo_enabled(tp))
-                       flags &= ~TH_SYN;
-               off--;
-               len++;
-               if (len > 0 && tp->t_state == TCPS_SYN_SENT) {
-                       while (inp->inp_sndinprog_cnt == 0 &&
-                               tp->t_pktlist_head != NULL) {
-                               packetlist = tp->t_pktlist_head;
-                               packchain_listadd = tp->t_lastchain;
-                               packchain_sent++;
-                               TCP_PKTLIST_CLEAR(tp);
-
-                               error = tcp_ip_output(so, tp, packetlist,
-                                   packchain_listadd, tp_inp_options,
-                                   (so_options & SO_DONTROUTE),
-                                   (sack_rxmit || (sack_bytes_rxmt != 0)),
-                                   isipv6);
+               if (tp->t_state == TCPS_SYN_RECEIVED && tfo_enabled(tp) && tp->snd_nxt == tp->snd_una + 1) {
+                       /* We are sending the SYN again! */
+                       off--;
+                       len++;
+               } else {
+                       if (tp->t_state != TCPS_SYN_RECEIVED || tfo_enabled(tp)) {
+                               flags &= ~TH_SYN;
                        }
 
-                       /*
-                        * tcp was closed while we were in ip,
-                        * resume close
-                        */
-                       if (inp->inp_sndinprog_cnt == 0 &&
-                               (tp->t_flags & TF_CLOSING)) {
-                               tp->t_flags &= ~TF_CLOSING;
-                               (void) tcp_close(tp);
-                       } else {
-                               tcp_check_timer_state(tp);
+                       off--;
+                       len++;
+                       if (len > 0 && tp->t_state == TCPS_SYN_SENT) {
+                               while (inp->inp_sndinprog_cnt == 0 &&
+                                       tp->t_pktlist_head != NULL) {
+                                       packetlist = tp->t_pktlist_head;
+                                       packchain_listadd = tp->t_lastchain;
+                                       packchain_sent++;
+                                       TCP_PKTLIST_CLEAR(tp);
+
+                                       error = tcp_ip_output(so, tp, packetlist,
+                                           packchain_listadd, tp_inp_options,
+                                           (so_options & SO_DONTROUTE),
+                                           (sack_rxmit || (sack_bytes_rxmt != 0)),
+                                           isipv6);
+                               }
+
+                               /*
+                                * tcp was closed while we were in ip,
+                                * resume close
+                                */
+                               if (inp->inp_sndinprog_cnt == 0 &&
+                                       (tp->t_flags & TF_CLOSING)) {
+                                       tp->t_flags &= ~TF_CLOSING;
+                                       (void) tcp_close(tp);
+                               } else {
+                                       tcp_check_timer_state(tp);
+                               }
+                               KERNEL_DEBUG(DBG_FNC_TCP_OUTPUT | DBG_FUNC_END,
+                                   0,0,0,0,0);
+                               return 0;
                        }
-                       KERNEL_DEBUG(DBG_FNC_TCP_OUTPUT | DBG_FUNC_END,
-                           0,0,0,0,0);
-                       return(0);
                }
        }
 
@@ -1029,6 +1036,12 @@ after_sack_rexmit:
                flags &= ~TH_FIN;
        }
 
+       /*
+        * Don't send a RST with data.
+        */
+       if (flags & TH_RST)
+               len = 0;
+
        if ((flags & TH_SYN) && tp->t_state <= TCPS_SYN_SENT && tfo_enabled(tp))
                len = tcp_tfo_check(tp, len);
 
@@ -1142,6 +1155,12 @@ after_sack_rexmit:
        }
 
 #if MPTCP
+       if (so->so_flags & SOF_MP_SUBFLOW && off < 0) {
+               os_log_error(mptcp_log_handle, "%s - %lx: offset is negative! len %d off %d\n",
+                   __func__, (unsigned long)VM_KERNEL_ADDRPERM(tp->t_mpsub->mpts_mpte),
+                   len, off);
+       }
+
        if ((so->so_flags & SOF_MP_SUBFLOW) &&
            !(tp->t_mpflags & TMPF_TCP_FALLBACK)) {
                int newlen = len;
@@ -1170,11 +1189,12 @@ after_sack_rexmit:
                 * option can be sent in one packet, reduce length to match
                 * the contiguous MPTCP level. Set sendalot to send remainder.
                 */
-               if (len > 0)
+               if (len > 0 && off >= 0) {
                        newlen = mptcp_adj_sendlen(so, off);
+               }
+
                if (newlen < len) {
                        len = newlen;
-                       sendalot = 1;
                }
        }
 #endif /* MPTCP */
@@ -1217,23 +1237,23 @@ after_sack_rexmit:
         * next expected input).  If the difference is at least two
         * max size segments, or at least 25% of the maximum possible
         * window, then want to send a window update to peer.
-        * Skip this if the connection is in T/TCP half-open state.
         */
        recwin = tcp_sbspace(tp);
-#if MPTCP
-       if (so->so_flags & SOF_MP_SUBFLOW) {
+
+       if (!(so->so_flags & SOF_MP_SUBFLOW)) {
+               if (recwin < (int32_t)(so->so_rcv.sb_hiwat / 4) &&
+                   recwin < (int)tp->t_maxseg) {
+                       recwin = 0;
+               }
+       } else {
                struct mptcb *mp_tp = tptomptp(tp);
+               struct socket *mp_so = mptetoso(mp_tp->mpt_mpte);
 
-               if (mp_tp != NULL) {
-                       mpte_lock_assert_held(mp_tp->mpt_mpte);
-                       recwin = imin(recwin, mptcp_sbspace(mp_tp));
+               if (recwin < (int32_t)(mp_so->so_rcv.sb_hiwat / 4) &&
+                   recwin < (int)tp->t_maxseg) {
+                       recwin = 0;
                }
        }
-#endif
-
-       if (recwin < (int32_t)(so->so_rcv.sb_hiwat / 4) &&
-           recwin < (int)tp->t_maxseg)
-               recwin = 0;
 
 #if TRAFFIC_MGT
        if (tcp_recv_bg == 1 || IS_TCP_RECV_BG(so)) {
@@ -1253,15 +1273,18 @@ after_sack_rexmit:
        if (recwin > (int32_t)(TCP_MAXWIN << tp->rcv_scale))
                recwin = (int32_t)(TCP_MAXWIN << tp->rcv_scale);
 
-       /*
-        * MPTCP needs to be able to announce a smaller window than previously,
-        * because the other subflow may have filled up the available window-
-        * space. So we have to be able to go backwards and announce a smaller
-        * window.
-        */
-       if (!(so->so_flags & SOF_MPTCP_TRUE) &&
-           recwin < (int32_t)(tp->rcv_adv - tp->rcv_nxt))
-               recwin = (int32_t)(tp->rcv_adv - tp->rcv_nxt);
+       if (!(so->so_flags & SOF_MP_SUBFLOW)) {
+               if (recwin < (int32_t)(tp->rcv_adv - tp->rcv_nxt)) {
+                       recwin = (int32_t)(tp->rcv_adv - tp->rcv_nxt);
+               }
+       } else {
+               struct mptcb *mp_tp = tptomptp(tp);
+
+               /* Don't remove what we announced at the MPTCP-layer */
+               if (recwin < (int32_t)(mp_tp->mpt_rcvadv - (uint32_t)mp_tp->mpt_rcvnxt)) {
+                       recwin = (int32_t)(mp_tp->mpt_rcvadv - (uint32_t)mp_tp->mpt_rcvnxt);
+               }
+       }
 
        /*
         * Sender silly window avoidance.   We transmit under the following
@@ -1283,6 +1306,16 @@ after_sack_rexmit:
                if (sack_rxmit)
                        goto send;
 
+               /*
+                * If this here is the first segment after SYN/ACK and TFO
+                * is being used, then we always send it, regardless of Nagle,...
+                */
+               if (tp->t_state == TCPS_SYN_RECEIVED &&
+                   tfo_enabled(tp) &&
+                   (tp->t_tfo_flags & TFO_F_COOKIE_VALID) &&
+                   tp->snd_nxt == tp->iss + 1)
+                       goto send;
+
                /*
                 * Send new data on the connection only if it is
                 * not flow controlled
@@ -1449,7 +1482,7 @@ just_return:
                tcp_check_timer_state(tp);
        }
        KERNEL_DEBUG(DBG_FNC_TCP_OUTPUT | DBG_FUNC_END, 0,0,0,0,0);
-       return (0);
+       return 0;
 
 send:
        /*
@@ -2024,12 +2057,12 @@ send:
                        goto out;
                }
                if (MHLEN < (hdrlen + max_linkhdr)) {
-                       MCLGET(m, M_DONTWAIT);
-                       if ((m->m_flags & M_EXT) == 0) {
-                               m_freem(m);
-                               error = ENOBUFS;
-                               goto out;
-                       }
+                       MCLGET(m, M_DONTWAIT);
+                       if ((m->m_flags & M_EXT) == 0) {
+                               m_freem(m);
+                               error = ENOBUFS;
+                               goto out;
+                       }
                }
                m->m_data += max_linkhdr;
                m->m_len = hdrlen;
@@ -2134,8 +2167,20 @@ send:
        }
        th->th_flags = flags;
        th->th_win = htons((u_short) (recwin>>tp->rcv_scale));
-       if (recwin > 0 && SEQ_LT(tp->rcv_adv, tp->rcv_nxt + recwin))
-               tp->rcv_adv = tp->rcv_nxt + recwin;
+       if (!(so->so_flags & SOF_MP_SUBFLOW)) {
+               if (recwin > 0 && SEQ_LT(tp->rcv_adv, tp->rcv_nxt + recwin)) {
+                       tp->rcv_adv = tp->rcv_nxt + recwin;
+               }
+       } else {
+               struct mptcb *mp_tp = tptomptp(tp);
+               if (recwin > 0) {
+                       tp->rcv_adv = tp->rcv_nxt + recwin;
+               }
+
+               if (recwin > 0 && SEQ_LT(mp_tp->mpt_rcvadv, (uint32_t)mp_tp->mpt_rcvnxt + recwin)) {
+                       mp_tp->mpt_rcvadv = (uint32_t)mp_tp->mpt_rcvnxt + recwin;
+               }
+       }
 
        /*
         * Adjust the RXWIN0SENT flag - indicate that we have advertised
@@ -2149,6 +2194,7 @@ send:
                tp->t_flags |= TF_RXWIN0SENT;
        else
                tp->t_flags &= ~TF_RXWIN0SENT;
+
        if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
                th->th_urp = htons((u_short)(tp->snd_up - tp->snd_nxt));
                th->th_flags |= TH_URG;
@@ -2287,13 +2333,13 @@ timer:
                 *
                 * Every time new data is sent PTO will get reset.
                 */
-               if (tcp_enable_tlp && tp->t_state == TCPS_ESTABLISHED &&
-                   SACK_ENABLED(tp) && !IN_FASTRECOVERY(tp)
-                   && tp->snd_nxt == tp->snd_max
-                   && SEQ_GT(tp->snd_nxt, tp->snd_una)
-                   && tp->t_rxtshift == 0
-                   && (tp->t_flagsext & (TF_SENT_TLPROBE|TF_PKTS_REORDERED)) == 0) {
-                       u_int32_t pto, srtt, new_rto = 0;
+               if (tcp_enable_tlp && len != 0 && tp->t_state == TCPS_ESTABLISHED &&
+                   SACK_ENABLED(tp) && !IN_FASTRECOVERY(tp) &&
+                   tp->snd_nxt == tp->snd_max &&
+                   SEQ_GT(tp->snd_nxt, tp->snd_una) &&
+                   tp->t_rxtshift == 0 &&
+                   (tp->t_flagsext & (TF_SENT_TLPROBE|TF_PKTS_REORDERED)) == 0) {
+                       u_int32_t pto, srtt;
 
                        /*
                         * Using SRTT alone to set PTO can cause spurious
@@ -2311,21 +2357,9 @@ timer:
                                pto = max(10, pto);
 
                        /* if RTO is less than PTO, choose RTO instead */
-                       if (tp->t_rxtcur < pto) {
-                               /*
-                                * Schedule PTO instead of RTO in favor of
-                                * fast recovery.
-                                */
+                       if (tp->t_rxtcur < pto)
                                pto = tp->t_rxtcur;
 
-                               /* Reset the next RTO to be after PTO. */
-                               TCPT_RANGESET(new_rto,
-                                   (pto + TCP_REXMTVAL(tp)),
-                                   max(tp->t_rttmin, tp->t_rttcur + 2),
-                                   TCPTV_REXMTMAX, 0);
-                               tp->t_timer[TCPT_REXMT] =
-                                   OFFSET_FROM_START(tp, new_rto);
-                       }
                        tp->t_timer[TCPT_PTO] = OFFSET_FROM_START(tp, pto);
                }
        } else {
@@ -2412,13 +2446,15 @@ timer:
 #if NECP
        {
                necp_kernel_policy_id policy_id;
+               necp_kernel_policy_id skip_policy_id;
                u_int32_t route_rule_id;
-               if (!necp_socket_is_allowed_to_send_recv(inp, &policy_id, &route_rule_id)) {
+               if (!necp_socket_is_allowed_to_send_recv(inp, NULL, &policy_id, &route_rule_id, &skip_policy_id)) {
+                       TCP_LOG_DROP_NECP(isipv6 ? (void *)ip6 : (void *)ip, th, tp, true);
                        m_freem(m);
                        error = EHOSTUNREACH;
                        goto out;
                }
-               necp_mark_packet_from_socket(m, inp, policy_id, route_rule_id);
+               necp_mark_packet_from_socket(m, inp, policy_id, route_rule_id, skip_policy_id);
 
                if (net_qos_policy_restricted != 0) {
                        necp_socket_update_qos_marking(inp, inp->inp_route.ro_rt,
@@ -2445,6 +2481,11 @@ timer:
        m->m_pkthdr.pkt_flowid = inp->inp_flowhash;
        m->m_pkthdr.pkt_flags |= (PKTF_FLOW_ID | PKTF_FLOW_LOCALSRC | PKTF_FLOW_ADV);
        m->m_pkthdr.pkt_proto = IPPROTO_TCP;
+       m->m_pkthdr.tx_tcp_pid = so->last_pid;
+       if (so->so_flags & SOF_DELEGATED)
+               m->m_pkthdr.tx_tcp_e_pid = so->e_pid;
+       else
+               m->m_pkthdr.tx_tcp_e_pid = 0;
 
        m->m_nextpkt = NULL;
 
@@ -2476,6 +2517,10 @@ timer:
                (void) m_set_service_class(m, so_tc2msc(sotc));
        }
 
+       TCP_LOG_TH_FLAGS(isipv6 ? (void *)ip6 : (void *)ip, th, tp, true,
+           inp->inp_last_outifp != NULL ? inp->inp_last_outifp :
+           inp->inp_boundifp);
+
        tp->t_pktlist_sentlen += len;
        tp->t_lastchain++;
 
@@ -2499,9 +2544,9 @@ timer:
                tp->t_pktlist_head = tp->t_pktlist_tail = m;
        }
 
-       if ((lro_ackmore) && (!sackoptlen) && (!tp->t_timer[TCPT_PERSIST]) &&
-                       ((th->th_flags & TH_ACK) == TH_ACK) && (!len) &&
-                       (tp->t_state == TCPS_ESTABLISHED)) {
+       if (lro_ackmore && !sackoptlen && tp->t_timer[TCPT_PERSIST] == 0 &&
+           (th->th_flags & TH_ACK) == TH_ACK && len == 0 &&
+           tp->t_state == TCPS_ESTABLISHED) {
                /* For a pure ACK, see if you need to send more of them */
                mnext = tcp_send_lroacks(tp, m, th);
                if (mnext) {
@@ -2559,7 +2604,7 @@ timer:
                        (tp->t_flags & TF_CLOSING)) {
                        tp->t_flags &= ~TF_CLOSING;
                        (void) tcp_close(tp);
-                       return (0);
+                       return 0;
                }
        } else {
                error = 0;
@@ -2607,9 +2652,14 @@ out:
                TCP_PKTLIST_CLEAR(tp);
 
                if (error == ENOBUFS) {
-                       if (!tp->t_timer[TCPT_REXMT] &&
-                           !tp->t_timer[TCPT_PERSIST] &&
-                           (SEQ_GT(tp->snd_max, tp->snd_una) ||
+                       /*
+                        * Set retransmit timer if not currently set
+                        * when we failed to send a segment that can be
+                        * retransmitted (i.e. not pure ack or rst)
+                        */
+                       if (tp->t_timer[TCPT_REXMT] == 0 &&
+                           tp->t_timer[TCPT_PERSIST] == 0 &&
+                           (len != 0 || (flags & (TH_SYN | TH_FIN)) != 0 ||
                            so->so_snd.sb_cc > 0))
                                tp->t_timer[TCPT_REXMT] =
                                        OFFSET_FROM_START(tp, tp->t_rxtcur);
@@ -2619,7 +2669,7 @@ out:
                        KERNEL_DEBUG(DBG_FNC_TCP_OUTPUT | DBG_FUNC_END, 0,0,0,0,0);
 
                        tcp_ccdbg_trace(tp, NULL, TCP_CC_OUTPUT_ERROR);
-                       return (0);
+                       return 0;
                }
                if (error == EMSGSIZE) {
                        /*
@@ -2655,7 +2705,7 @@ out:
                }
                tcp_check_timer_state(tp);
                KERNEL_DEBUG(DBG_FNC_TCP_OUTPUT | DBG_FUNC_END, 0,0,0,0,0);
-               return (error);
+               return error;
        }
 
        tcpstat.tcps_sndtotal++;
@@ -2665,7 +2715,8 @@ out:
                goto again;
 
        tcp_check_timer_state(tp);
-       return (0);
+
+       return 0;
 }
 
 static int
@@ -2677,16 +2728,25 @@ tcp_ip_output(struct socket *so, struct tcpcb *tp, struct mbuf *pkt,
        boolean_t unlocked = FALSE;
        boolean_t ifdenied = FALSE;
        struct inpcb *inp = tp->t_inpcb;
-       struct ip_out_args ipoa =
-           { IFSCOPE_NONE, { 0 }, IPOAF_SELECT_SRCIF|IPOAF_BOUND_SRCADDR, 0,
-           SO_TC_UNSPEC, _NET_SERVICE_TYPE_UNSPEC };
+       struct ip_out_args ipoa;
        struct route ro;
        struct ifnet *outif = NULL;
+
+       bzero(&ipoa, sizeof(ipoa));
+       ipoa.ipoa_boundif = IFSCOPE_NONE;
+       ipoa.ipoa_flags = IPOAF_SELECT_SRCIF | IPOAF_BOUND_SRCADDR;
+       ipoa.ipoa_sotc = SO_TC_UNSPEC;
+       ipoa.ipoa_netsvctype = _NET_SERVICE_TYPE_UNSPEC;
 #if INET6
-       struct ip6_out_args ip6oa =
-           { IFSCOPE_NONE, { 0 }, IP6OAF_SELECT_SRCIF|IP6OAF_BOUND_SRCADDR, 0,
-           SO_TC_UNSPEC, _NET_SERVICE_TYPE_UNSPEC };
+       struct ip6_out_args ip6oa;
        struct route_in6 ro6;
+
+       bzero(&ip6oa, sizeof(ip6oa));
+       ip6oa.ip6oa_boundif = IFSCOPE_NONE;
+       ip6oa.ip6oa_flags = IP6OAF_SELECT_SRCIF | IP6OAF_BOUND_SRCADDR;
+       ip6oa.ip6oa_sotc = SO_TC_UNSPEC;
+       ip6oa.ip6oa_netsvctype = _NET_SERVICE_TYPE_UNSPEC;
+
        struct flowadv *adv =
            (isipv6 ? &ip6oa.ip6oa_flowadv : &ipoa.ipoa_flowadv);
 #else /* INET6 */
@@ -2724,6 +2784,14 @@ tcp_ip_output(struct socket *so, struct tcpcb *tp, struct mbuf *pkt,
                        ipoa.ipoa_flags |=  IPOAF_NO_EXPENSIVE;
 
        }
+       if (INP_NO_CONSTRAINED(inp)) {
+#if INET6
+               if (isipv6)
+                       ip6oa.ip6oa_flags |=  IP6OAF_NO_CONSTRAINED;
+               else
+#endif /* INET6 */
+                       ipoa.ipoa_flags |=  IPOAF_NO_CONSTRAINED;
+       }
        if (INP_AWDL_UNRESTRICTED(inp)) {
 #if INET6
                if (isipv6)
@@ -2814,7 +2882,6 @@ tcp_ip_output(struct socket *so, struct tcpcb *tp, struct mbuf *pkt,
 #endif
                ; // I'm important, not extraneous
 
-
        while (pkt != NULL) {
                struct mbuf *npkt = pkt->m_nextpkt;
 
@@ -2823,7 +2890,7 @@ tcp_ip_output(struct socket *so, struct tcpcb *tp, struct mbuf *pkt,
                        /*
                         * If we are not chaining, make sure to set the packet
                         * list count to 0 so that IP takes the right path;
-                        * this is important for cases such as IPSec where a
+                        * this is important for cases such as IPsec where a
                         * single mbuf might result in multiple mbufs as part
                         * of the encapsulation.  If a non-zero count is passed
                         * down to IP, the head of the chain might change and
@@ -2893,22 +2960,33 @@ tcp_ip_output(struct socket *so, struct tcpcb *tp, struct mbuf *pkt,
                error = ENOBUFS;
 
        VERIFY(inp->inp_sndinprog_cnt > 0);
-       if ( --inp->inp_sndinprog_cnt == 0)
+       if ( --inp->inp_sndinprog_cnt == 0) {
                inp->inp_flags &= ~(INP_FC_FEEDBACK);
+               if (inp->inp_sndingprog_waiters > 0) {
+                       wakeup(&inp->inp_sndinprog_cnt);
+               }
+       }
 
 #if INET6
        if (isipv6) {
-               if (ro6.ro_rt != NULL)
+               /*
+                * When an NECP IP tunnel policy forces the outbound interface,
+                * ip6_output_list() informs the transport layer what is the actual
+                * outgoing interface
+                */
+               if (ip6oa.ip6oa_flags & IP6OAF_BOUND_IF) {
+                       outif = ifindex2ifnet[ip6oa.ip6oa_boundif];
+               } else if (ro6.ro_rt != NULL) {
                        outif = ro6.ro_rt->rt_ifp;
+               }
        } else
 #endif /* INET6 */
                if (ro.ro_rt != NULL)
                        outif = ro.ro_rt->rt_ifp;
 
-       if (outif != NULL && outif != inp->inp_last_outifp &&
-           so->so_snd.sb_cc > 0) {
+       if (outif != NULL && outif != inp->inp_last_outifp) {
                /* Update the send byte count */
-               if (so->so_snd.sb_flags & SB_SNDBYTE_CNT) {
+               if (so->so_snd.sb_cc > 0 && so->so_snd.sb_flags & SB_SNDBYTE_CNT) {
                        inp_decr_sndbytes_total(so, so->so_snd.sb_cc);
                        inp_decr_sndbytes_allunsent(so, tp->snd_una);
                        so->so_snd.sb_flags &= ~SB_SNDBYTE_CNT;
@@ -2918,7 +2996,7 @@ tcp_ip_output(struct socket *so, struct tcpcb *tp, struct mbuf *pkt,
        }
 
        if (error != 0 && ifdenied &&
-           (INP_NO_CELLULAR(inp) || INP_NO_EXPENSIVE(inp)))
+           (INP_NO_CELLULAR(inp) || INP_NO_EXPENSIVE(inp) || INP_NO_CONSTRAINED(inp)))
                soevent(so,
                    (SO_FILT_HINT_LOCKED|SO_FILT_HINT_IFDENIED));
 
@@ -2938,7 +3016,7 @@ tcp_ip_output(struct socket *so, struct tcpcb *tp, struct mbuf *pkt,
                tcp_getrt_rtt(tp, tp->t_inpcb->in6p_route.ro_rt);
                tp->t_timer[TCPT_REXMT] = OFFSET_FROM_START(tp, tp->t_rxtcur);
        }
-       return (error);
+       return error;
 }
 
 int tcptv_persmin_val = TCPTV_PERSMIN;
@@ -2954,9 +3032,9 @@ tcp_setpersist(struct tcpcb *tp)
         * see rdar://5805356
         */
 
-       if ((tp->t_persist_timeout != 0) &&
-                   (tp->t_timer[TCPT_PERSIST] == 0) &&
-                   (tp->t_persist_stop == 0)) {
+       if (tp->t_persist_timeout != 0 &&
+           tp->t_timer[TCPT_PERSIST] == 0 &&
+           tp->t_persist_stop == 0) {
                tp->t_persist_stop = tcp_now + tp->t_persist_timeout;
        }
 
@@ -3089,7 +3167,7 @@ tcp_recv_throttle (struct tcpcb *tp)
                 * in that state until rtt comes closer to base rtt
                 */
                if (tp->t_flagsext & TF_RECV_THROTTLE)
-                       return (1);
+                       return 1;
 
                base_rtt = get_base_rtt(tp);
 
@@ -3115,9 +3193,9 @@ tcp_recv_throttle (struct tcpcb *tp)
                                            tcp_recv_throttle_minwin);
                                        sbrcv->sb_idealsize = newsize;
                                }
-                               return (1);
+                               return 1;
                        } else {
-                               return (0);
+                               return 0;
                        }
                }
        }
@@ -3127,7 +3205,7 @@ tcp_recv_throttle (struct tcpcb *tp)
         * measurement. Use IPDV in this case.
         */
        if (tp->acc_iaj > tcp_acc_iaj_react_limit)
-               return (1);
+               return 1;
 
-       return (0);
+       return 0;
 }