/* * INET An implementation of the TCP/IP protocol suite for the LINUX * operating system. INET is implemented using the BSD Socket * interface as the means of communication with the user level. * * Implementation of the Transmission Control Protocol(TCP). * * Authors: Ross Biro * Fred N. van Kempen, * Mark Evans, * Corey Minyard * Florian La Roche, * Charles Hedrick, * Linus Torvalds, * Alan Cox, * Matthew Dillon, * Arnt Gulbrandsen, * Jorge Cwik, */ #include #include #include int sysctl_tcp_thin_linear_timeouts __read_mostly; /** * tcp_write_err() - close socket and save error info * @sk: The socket the error has appeared on. * * Returns: Nothing (void) */ static void tcp_write_err(struct sock *sk) { sk->sk_err = sk->sk_err_soft ? : ETIMEDOUT; sk->sk_error_report(sk); tcp_done(sk); __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONTIMEOUT); } /** * tcp_out_of_resources() - Close socket if out of resources * @sk: pointer to current socket * @do_reset: send a last packet with reset flag * * Do not allow orphaned sockets to eat all our resources. * This is direct violation of TCP specs, but it is required * to prevent DoS attacks. It is called when a retransmission timeout * or zero probe timeout occurs on orphaned socket. * * Criteria is still not confirmed experimentally and may change. * We kill the socket, if: * 1. If number of orphaned sockets exceeds an administratively configured * limit. * 2. If we have strong memory pressure. */ static int tcp_out_of_resources(struct sock *sk, bool do_reset) { struct tcp_sock *tp = tcp_sk(sk); int shift = 0; /* If peer does not open window for long time, or did not transmit * anything for long time, penalize it. */ if ((s32)(tcp_time_stamp - tp->lsndtime) > 2*TCP_RTO_MAX || !do_reset) shift++; /* If some dubious ICMP arrived, penalize even more. */ if (sk->sk_err_soft) shift++; if (tcp_check_oom(sk, shift)) { /* Catch exceptional cases, when connection requires reset. * 1. Last segment was sent recently. */ if ((s32)(tcp_time_stamp - tp->lsndtime) <= TCP_TIMEWAIT_LEN || /* 2. Window is closed. */ (!tp->snd_wnd && !tp->packets_out)) do_reset = true; if (do_reset) tcp_send_active_reset(sk, GFP_ATOMIC); tcp_done(sk); __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONMEMORY); return 1; } return 0; } /** * tcp_orphan_retries() - Returns maximal number of retries on an orphaned socket * @sk: Pointer to the current socket. * @alive: bool, socket alive state */ static int tcp_orphan_retries(struct sock *sk, bool alive) { int retries = sock_net(sk)->ipv4.sysctl_tcp_orphan_retries; /* May be zero. */ /* We know from an ICMP that something is wrong. */ if (sk->sk_err_soft && !alive) retries = 0; /* However, if socket sent something recently, select some safe * number of retries. 8 corresponds to >100 seconds with minimal * RTO of 200msec. */ if (retries == 0 && alive) retries = 8; return retries; } static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk) { struct net *net = sock_net(sk); /* Black hole detection */ if (net->ipv4.sysctl_tcp_mtu_probing) { if (!icsk->icsk_mtup.enabled) { icsk->icsk_mtup.enabled = 1; icsk->icsk_mtup.probe_timestamp = tcp_time_stamp; tcp_sync_mss(sk, icsk->icsk_pmtu_cookie); } else { struct net *net = sock_net(sk); struct tcp_sock *tp = tcp_sk(sk); int mss; mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1; mss = min(net->ipv4.sysctl_tcp_base_mss, mss); mss = max(mss, 68 - tp->tcp_header_len); icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss); tcp_sync_mss(sk, icsk->icsk_pmtu_cookie); } } } /** * retransmits_timed_out() - returns true if this connection has timed out * @sk: The current socket * @boundary: max number of retransmissions * @timeout: A custom timeout value. * If set to 0 the default timeout is calculated and used. * Using TCP_RTO_MIN and the number of unsuccessful retransmits. * @syn_set: true if the SYN Bit was set. * * The default "timeout" value this function can calculate and use * is equivalent to the timeout of a TCP Connection * after "boundary" unsuccessful, exponentially backed-off * retransmissions with an initial RTO of TCP_RTO_MIN or TCP_TIMEOUT_INIT if * syn_set flag is set. * */ static bool retransmits_timed_out(struct sock *sk, unsigned int boundary, unsigned int timeout, bool syn_set) { unsigned int linear_backoff_thresh, start_ts; unsigned int rto_base = syn_set ? TCP_TIMEOUT_INIT : TCP_RTO_MIN; if (!inet_csk(sk)->icsk_retransmits) return false; start_ts = tcp_sk(sk)->retrans_stamp; if (unlikely(!start_ts)) start_ts = tcp_skb_timestamp(tcp_write_queue_head(sk)); if (likely(timeout == 0)) { linear_backoff_thresh = ilog2(TCP_RTO_MAX/rto_base); if (boundary <= linear_backoff_thresh) timeout = ((2 << boundary) - 1) * rto_base; else timeout = ((2 << linear_backoff_thresh) - 1) * rto_base + (boundary - linear_backoff_thresh) * TCP_RTO_MAX; } return (tcp_time_stamp - start_ts) >= timeout; } /* A write timeout has occurred. Process the after effects. */ static int tcp_write_timeout(struct sock *sk) { struct inet_connection_sock *icsk = inet_csk(sk); struct tcp_sock *tp = tcp_sk(sk); struct net *net = sock_net(sk); int retry_until; bool do_reset, syn_set = false; if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) { if (icsk->icsk_retransmits) { dst_negative_advice(sk); if (tp->syn_fastopen || tp->syn_data) tcp_fastopen_cache_set(sk, 0, NULL, true, 0); if (tp->syn_data && icsk->icsk_retransmits == 1) NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENACTIVEFAIL); } retry_until = icsk->icsk_syn_retries ? : net->ipv4.sysctl_tcp_syn_retries; syn_set = true; } else { if (retransmits_timed_out(sk, net->ipv4.sysctl_tcp_retries1, 0, 0)) { /* Some middle-boxes may black-hole Fast Open _after_ * the handshake. Therefore we conservatively disable * Fast Open on this path on recurring timeouts with * few or zero bytes acked after Fast Open. */ if (tp->syn_data_acked && tp->bytes_acked <= tp->rx_opt.mss_clamp) { tcp_fastopen_cache_set(sk, 0, NULL, true, 0); if (icsk->icsk_retransmits == net->ipv4.sysctl_tcp_retries1) NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENACTIVEFAIL); } /* Black hole detection */ tcp_mtu_probing(icsk, sk); dst_negative_advice(sk); } retry_until = net->ipv4.sysctl_tcp_retries2; if (sock_flag(sk, SOCK_DEAD)) { const bool alive = icsk->icsk_rto < TCP_RTO_MAX; retry_until = tcp_orphan_retries(sk, alive); do_reset = alive || !retransmits_timed_out(sk, retry_until, 0, 0); if (tcp_out_of_resources(sk, do_reset)) return 1; } } if (retransmits_timed_out(sk, retry_until, syn_set ? 0 : icsk->icsk_user_timeout, syn_set)) { /* Has it gone just too far? */ tcp_write_err(sk); return 1; } return 0; } /* Called with BH disabled */ void tcp_delack_timer_handler(struct sock *sk) { struct tcp_sock *tp = tcp_sk(sk); struct inet_connection_sock *icsk = inet_csk(sk); sk_mem_reclaim_partial(sk); if (sk->sk_state == TCP_CLOSE || !(icsk->icsk_ack.pending & ICSK_ACK_TIMER)) goto out; if (time_after(icsk->icsk_ack.timeout, jiffies)) { sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout); goto out; } icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER; if (!skb_queue_empty(&tp->ucopy.prequeue)) { struct sk_buff *skb; __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSCHEDULERFAILED); while ((skb = __skb_dequeue(&tp->ucopy.prequeue)) != NULL) sk_backlog_rcv(sk, skb); tp->ucopy.memory = 0; } if (inet_csk_ack_scheduled(sk)) { if (!icsk->icsk_ack.pingpong) { /* Delayed ACK missed: inflate ATO. */ icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1, icsk->icsk_rto); } else { /* Delayed ACK missed: leave pingpong mode and * deflate ATO. */ icsk->icsk_ack.pingpong = 0; icsk->icsk_ack.ato = TCP_ATO_MIN; } tcp_send_ack(sk); __NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKS); } out: if (tcp_under_memory_pressure(sk)) sk_mem_reclaim(sk); } /** * tcp_delack_timer() - The TCP delayed ACK timeout handler * @data: Pointer to the current socket. (gets casted to struct sock *) * * This function gets (indirectly) called when the kernel timer for a TCP packet * of this socket expires. Calls tcp_delack_timer_handler() to do the actual work. * * Returns: Nothing (void) */ static void tcp_delack_timer(unsigned long data) { struct sock *sk = (struct sock *)data; bh_lock_sock(sk); if (!sock_owned_by_user(sk)) { tcp_delack_timer_handler(sk); } else { inet_csk(sk)->icsk_ack.blocked = 1; __NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED); /* deleguate our work to tcp_release_cb() */ if (!test_and_set_bit(TCP_DELACK_TIMER_DEFERRED, &tcp_sk(sk)->tsq_flags)) sock_hold(sk); } bh_unlock_sock(sk); sock_put(sk); } static void tcp_probe_timer(struct sock *sk) { struct inet_connection_sock *icsk = inet_csk(sk); struct tcp_sock *tp = tcp_sk(sk); int max_probes; u32 start_ts; if (tp->packets_out || !tcp_send_head(sk)) { icsk->icsk_probes_out = 0; return; } /* RFC 1122 4.2.2.17 requires the sender to stay open indefinitely as * long as the receiver continues to respond probes. We support this by * default and reset icsk_probes_out with incoming ACKs. But if the * socket is orphaned or the user specifies TCP_USER_TIMEOUT, we * kill the socket when the retry count and the time exceeds the * corresponding system limit. We also implement similar policy when * we use RTO to probe window in tcp_retransmit_timer(). */ start_ts = tcp_skb_timestamp(tcp_send_head(sk)); if (!start_ts) skb_mstamp_get(&tcp_send_head(sk)->skb_mstamp); else if (icsk->icsk_user_timeout && (s32)(tcp_time_stamp - start_ts) > icsk->icsk_user_timeout) goto abort; max_probes = sock_net(sk)->ipv4.sysctl_tcp_retries2; if (sock_flag(sk, SOCK_DEAD)) { const bool alive = inet_csk_rto_backoff(icsk, TCP_RTO_MAX) < TCP_RTO_MAX; max_probes = tcp_orphan_retries(sk, alive); if (!alive && icsk->icsk_backoff >= max_probes) goto abort; if (tcp_out_of_resources(sk, true)) return; } if (icsk->icsk_probes_out > max_probes) { abort: tcp_write_err(sk); } else { /* Only send another probe if we didn't close things up. */ tcp_send_probe0(sk); } } /* * Timer for Fast Open socket to retransmit SYNACK. Note that the * sk here is the child socket, not the parent (listener) socket. */ static void tcp_fastopen_synack_timer(struct sock *sk) { struct inet_connection_sock *icsk = inet_csk(sk); int max_retries = icsk->icsk_syn_retries ? : sock_net(sk)->ipv4.sysctl_tcp_synack_retries + 1; /* add one more retry for fastopen */ struct request_sock *req; req = tcp_sk(sk)->fastopen_rsk; req->rsk_ops->syn_ack_timeout(req); if (req->num_timeout >= max_retries) { tcp_write_err(sk); return; } /* XXX (TFO) - Unlike regular SYN-ACK retransmit, we ignore error * returned from rtx_syn_ack() to make it more persistent like * regular retransmit because if the child socket has been accepted * it's not good to give up too easily. */ inet_rtx_syn_ack(sk, req); req->num_timeout++; icsk->icsk_retransmits++; inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, TCP_TIMEOUT_INIT << req->num_timeout, TCP_RTO_MAX); } /** * tcp_retransmit_timer() - The TCP retransmit timeout handler * @sk: Pointer to the current socket. * * This function gets called when the kernel timer for a TCP packet * of this socket expires. * * It handles retransmission, timer adjustment and other necesarry measures. * * Returns: Nothing (void) */ void tcp_retransmit_timer(struct sock *sk) { struct tcp_sock *tp = tcp_sk(sk); struct net *net = sock_net(sk); struct inet_connection_sock *icsk = inet_csk(sk); if (tp->fastopen_rsk) { WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV && sk->sk_state != TCP_FIN_WAIT1); tcp_fastopen_synack_timer(sk); /* Before we receive ACK to our SYN-ACK don't retransmit * anything else (e.g., data or FIN segments). */ return; } if (!tp->packets_out) goto out; WARN_ON(tcp_write_queue_empty(sk)); tp->tlp_high_seq = 0; if (!tp->snd_wnd && !sock_flag(sk, SOCK_DEAD) && !((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))) { /* Receiver dastardly shrinks window. Our retransmits * become zero probes, but we should not timeout this * connection. If the socket is an orphan, time it out, * we cannot allow such beasts to hang infinitely. */ struct inet_sock *inet = inet_sk(sk); if (sk->sk_family == AF_INET) { net_dbg_ratelimited("Peer %pI4:%u/%u unexpectedly shrunk window %u:%u (repaired)\n", &inet->inet_daddr, ntohs(inet->inet_dport), inet->inet_num, tp->snd_una, tp->snd_nxt); } #if IS_ENABLED(CONFIG_IPV6) else if (sk->sk_family == AF_INET6) { net_dbg_ratelimited("Peer %pI6:%u/%u unexpectedly shrunk window %u:%u (repaired)\n", &sk->sk_v6_daddr, ntohs(inet->inet_dport), inet->inet_num, tp->snd_una, tp->snd_nxt); } #endif if (tcp_time_stamp - tp->rcv_tstamp > TCP_RTO_MAX) { tcp_write_err(sk); goto out; } tcp_enter_loss(sk); tcp_retransmit_skb(sk, tcp_write_queue_head(sk), 1); __sk_dst_reset(sk); goto out_reset_timer; } if (tcp_write_timeout(sk)) goto out; if (icsk->icsk_retransmits == 0) { int mib_idx; if (icsk->icsk_ca_state == TCP_CA_Recovery) { if (tcp_is_sack(tp)) mib_idx = LINUX_MIB_TCPSACKRECOVERYFAIL; else mib_idx = LINUX_MIB_TCPRENORECOVERYFAIL; } else if (icsk->icsk_ca_state == TCP_CA_Loss) { mib_idx = LINUX_MIB_TCPLOSSFAILURES; } else if ((icsk->icsk_ca_state == TCP_CA_Disorder) || tp->sacked_out) { if (tcp_is_sack(tp)) mib_idx = LINUX_MIB_TCPSACKFAILURES; else mib_idx = LINUX_MIB_TCPRENOFAILURES; } else { mib_idx = LINUX_MIB_TCPTIMEOUTS; } __NET_INC_STATS(sock_net(sk), mib_idx); } tcp_enter_loss(sk); if (tcp_retransmit_skb(sk, tcp_write_queue_head(sk), 1) > 0) { /* Retransmission failed because of local congestion, * do not backoff. */ if (!icsk->icsk_retransmits) icsk->icsk_retransmits = 1; inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, min(icsk->icsk_rto, TCP_RESOURCE_PROBE_INTERVAL), TCP_RTO_MAX); goto out; } /* Increase the timeout each time we retransmit. Note that * we do not increase the rtt estimate. rto is initialized * from rtt, but increases here. Jacobson (SIGCOMM 88) suggests * that doubling rto each time is the least we can get away with. * In KA9Q, Karn uses this for the first few times, and then * goes to quadratic. netBSD doubles, but only goes up to *64, * and clamps at 1 to 64 sec afterwards. Note that 120 sec is * defined in the protocol as the maximum possible RTT. I guess * we'll have to use something other than TCP to talk to the * University of Mars. * * PAWS allows us longer timeouts and large windows, so once * implemented ftp to mars will work nicely. We will have to fix * the 120 second clamps though! */ icsk->icsk_backoff++; icsk->icsk_retransmits++; out_reset_timer: /* If stream is thin, use linear timeouts. Since 'icsk_backoff' is * used to reset timer, set to 0. Recalculate 'icsk_rto' as this * might be increased if the stream oscillates between thin and thick, * thus the old value might already be too high compared to the value * set by 'tcp_set_rto' in tcp_input.c which resets the rto without * backoff. Limit to TCP_THIN_LINEAR_RETRIES before initiating * exponential backoff behaviour to avoid continue hammering * linear-timeout retransmissions into a black hole */ if (sk->sk_state == TCP_ESTABLISHED && (tp->thin_lto || sysctl_tcp_thin_linear_timeouts) && tcp_stream_is_thin(tp) && icsk->icsk_retransmits <= TCP_THIN_LINEAR_RETRIES) { icsk->icsk_backoff = 0; icsk->icsk_rto = min(__tcp_set_rto(tp), TCP_RTO_MAX); } else { /* Use normal (exponential) backoff */ icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX); } inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto, TCP_RTO_MAX); if (retransmits_timed_out(sk, net->ipv4.sysctl_tcp_retries1 + 1, 0, 0)) __sk_dst_reset(sk); out:; } /* Called with bottom-half processing disabled. Called by tcp_write_timer() */ void tcp_write_timer_handler(struct sock *sk) { struct inet_connection_sock *icsk = inet_csk(sk); int event; if (sk->sk_state == TCP_CLOSE || !icsk->icsk_pending) goto out; if (time_after(icsk->icsk_timeout, jiffies)) { sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout); goto out; } event = icsk->icsk_pending; switch (event) { case ICSK_TIME_EARLY_RETRANS: tcp_resume_early_retransmit(sk); break; case ICSK_TIME_LOSS_PROBE: tcp_send_loss_probe(sk); break; case ICSK_TIME_RETRANS: icsk->icsk_pending = 0; tcp_retransmit_timer(sk); break; case ICSK_TIME_PROBE0: icsk->icsk_pending = 0; tcp_probe_timer(sk); break; } out: sk_mem_reclaim(sk); } static void tcp_write_timer(unsigned long data) { struct sock *sk = (struct sock *)data; bh_lock_sock(sk); if (!sock_owned_by_user(sk)) { tcp_write_timer_handler(sk); } else { /* delegate our work to tcp_release_cb() */ if (!test_and_set_bit(TCP_WRITE_TIMER_DEFERRED, &tcp_sk(sk)->tsq_flags)) sock_hold(sk); } bh_unlock_sock(sk); sock_put(sk); } void tcp_syn_ack_timeout(const struct request_sock *req) { struct net *net = read_pnet(&inet_rsk(req)->ireq_net); __NET_INC_STATS(net, LINUX_MIB_TCPTIMEOUTS); } EXPORT_SYMBOL(tcp_syn_ack_timeout); void tcp_set_keepalive(struct sock *sk, int val) { if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)) return; if (val && !sock_flag(sk, SOCK_KEEPOPEN)) inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tcp_sk(sk))); else if (!val) inet_csk_delete_keepalive_timer(sk); } static void tcp_keepalive_timer (unsigned long data) { struct sock *sk = (struct sock *) data; struct inet_connection_sock *icsk = inet_csk(sk); struct tcp_sock *tp = tcp_sk(sk); u32 elapsed; /* Only process if socket is not in use. */ bh_lock_sock(sk); if (sock_owned_by_user(sk)) { /* Try again later. */ inet_csk_reset_keepalive_timer (sk, HZ/20); goto out; } if (sk->sk_state == TCP_LISTEN) { pr_err("Hmm... keepalive on a LISTEN ???\n"); goto out; } if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) { if (tp->linger2 >= 0) { const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN; if (tmo > 0) { tcp_time_wait(sk, TCP_FIN_WAIT2, tmo); goto out; } } tcp_send_active_reset(sk, GFP_ATOMIC); goto death; } if (!sock_flag(sk, SOCK_KEEPOPEN) || sk->sk_state == TCP_CLOSE) goto out; elapsed = keepalive_time_when(tp); /* It is alive without keepalive 8) */ if (tp->packets_out || tcp_send_head(sk)) goto resched; elapsed = keepalive_time_elapsed(tp); if (elapsed >= keepalive_time_when(tp)) { /* If the TCP_USER_TIMEOUT option is enabled, use that * to determine when to timeout instead. */ if ((icsk->icsk_user_timeout != 0 && elapsed >= icsk->icsk_user_timeout && icsk->icsk_probes_out > 0) || (icsk->icsk_user_timeout == 0 && icsk->icsk_probes_out >= keepalive_probes(tp))) { tcp_send_active_reset(sk, GFP_ATOMIC); tcp_write_err(sk); goto out; } if (tcp_write_wakeup(sk, LINUX_MIB_TCPKEEPALIVE) <= 0) { icsk->icsk_probes_out++; elapsed = keepalive_intvl_when(tp); } else { /* If keepalive was lost due to local congestion, * try harder. */ elapsed = TCP_RESOURCE_PROBE_INTERVAL; } } else { /* It is tp->rcv_tstamp + keepalive_time_when(tp) */ elapsed = keepalive_time_when(tp) - elapsed; } sk_mem_reclaim(sk); resched: inet_csk_reset_keepalive_timer (sk, elapsed); goto out; death: tcp_done(sk); out: bh_unlock_sock(sk); sock_put(sk); } void tcp_init_xmit_timers(struct sock *sk) { inet_csk_init_xmit_timers(sk, &tcp_write_timer, &tcp_delack_timer, &tcp_keepalive_timer); }