diff options
Diffstat (limited to 'net/ipv4/tcp_timer.c')
-rw-r--r-- | net/ipv4/tcp_timer.c | 599 |
1 files changed, 599 insertions, 0 deletions
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c new file mode 100644 index 00000000..34d4a02c --- /dev/null +++ b/net/ipv4/tcp_timer.c @@ -0,0 +1,599 @@ +/* + * 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, <waltje@uWalt.NL.Mugnet.ORG> + * Mark Evans, <evansmp@uhura.aston.ac.uk> + * Corey Minyard <wf-rch!minyard@relay.EU.net> + * Florian La Roche, <flla@stud.uni-sb.de> + * Charles Hedrick, <hedrick@klinzhai.rutgers.edu> + * Linus Torvalds, <torvalds@cs.helsinki.fi> + * Alan Cox, <gw4pts@gw4pts.ampr.org> + * Matthew Dillon, <dillon@apollo.west.oic.com> + * Arnt Gulbrandsen, <agulbra@nvg.unit.no> + * Jorge Cwik, <jorge@laser.satlink.net> + */ + +#include <linux/module.h> +#include <linux/gfp.h> +#include <net/tcp.h> + +int sysctl_tcp_syn_retries __read_mostly = TCP_SYN_RETRIES; +int sysctl_tcp_synack_retries __read_mostly = TCP_SYNACK_RETRIES; +int sysctl_tcp_keepalive_time __read_mostly = TCP_KEEPALIVE_TIME; +int sysctl_tcp_keepalive_probes __read_mostly = TCP_KEEPALIVE_PROBES; +int sysctl_tcp_keepalive_intvl __read_mostly = TCP_KEEPALIVE_INTVL; +int sysctl_tcp_retries1 __read_mostly = TCP_RETR1; +int sysctl_tcp_retries2 __read_mostly = TCP_RETR2; +int sysctl_tcp_orphan_retries __read_mostly; +int sysctl_tcp_thin_linear_timeouts __read_mostly; + +static void tcp_write_timer(unsigned long); +static void tcp_delack_timer(unsigned long); +static void tcp_keepalive_timer (unsigned long data); + +void tcp_init_xmit_timers(struct sock *sk) +{ + inet_csk_init_xmit_timers(sk, &tcp_write_timer, &tcp_delack_timer, + &tcp_keepalive_timer); +} +EXPORT_SYMBOL(tcp_init_xmit_timers); + +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_BH(sock_net(sk), LINUX_MIB_TCPABORTONTIMEOUT); +} + +/* 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, int 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 = 1; + if (do_reset) + tcp_send_active_reset(sk, GFP_ATOMIC); + tcp_done(sk); + NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONMEMORY); + return 1; + } + return 0; +} + +/* Calculate maximal number or retries on an orphaned socket. */ +static int tcp_orphan_retries(struct sock *sk, int alive) +{ + int retries = 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) +{ + /* Black hole detection */ + if (sysctl_tcp_mtu_probing) { + if (!icsk->icsk_mtup.enabled) { + icsk->icsk_mtup.enabled = 1; + tcp_sync_mss(sk, icsk->icsk_pmtu_cookie); + } else { + struct tcp_sock *tp = tcp_sk(sk); + int mss; + + mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1; + mss = min(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); + } + } +} + +/* This function calculates a "timeout" which 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; + + if (unlikely(!tcp_sk(sk)->retrans_stamp)) + start_ts = TCP_SKB_CB(tcp_write_queue_head(sk))->when; + else + start_ts = tcp_sk(sk)->retrans_stamp; + + 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); + 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); + retry_until = icsk->icsk_syn_retries ? : sysctl_tcp_syn_retries; + syn_set = true; + } else { + if (retransmits_timed_out(sk, sysctl_tcp_retries1, 0, 0)) { + /* Black hole detection */ + tcp_mtu_probing(icsk, sk); + + dst_negative_advice(sk); + } + + retry_until = sysctl_tcp_retries2; + if (sock_flag(sk, SOCK_DEAD)) { + const int 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; +} + +static void tcp_delack_timer(unsigned long data) +{ + struct sock *sk = (struct sock *)data; + struct tcp_sock *tp = tcp_sk(sk); + struct inet_connection_sock *icsk = inet_csk(sk); + + bh_lock_sock(sk); + if (sock_owned_by_user(sk)) { + /* Try again later. */ + icsk->icsk_ack.blocked = 1; + NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED); + sk_reset_timer(sk, &icsk->icsk_delack_timer, jiffies + TCP_DELACK_MIN); + goto out_unlock; + } + + 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_BH(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_BH(sock_net(sk), LINUX_MIB_DELAYEDACKS); + } + +out: + if (sk_under_memory_pressure(sk)) + sk_mem_reclaim(sk); +out_unlock: + 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; + + if (tp->packets_out || !tcp_send_head(sk)) { + icsk->icsk_probes_out = 0; + return; + } + + /* *WARNING* RFC 1122 forbids this + * + * It doesn't AFAIK, because we kill the retransmit timer -AK + * + * FIXME: We ought not to do it, Solaris 2.5 actually has fixing + * this behaviour in Solaris down as a bug fix. [AC] + * + * Let me to explain. icsk_probes_out is zeroed by incoming ACKs + * even if they advertise zero window. Hence, connection is killed only + * if we received no ACKs for normal connection timeout. It is not killed + * only because window stays zero for some time, window may be zero + * until armageddon and even later. We are in full accordance + * with RFCs, only probe timer combines both retransmission timeout + * and probe timeout in one bottle. --ANK + */ + max_probes = sysctl_tcp_retries2; + + if (sock_flag(sk, SOCK_DEAD)) { + const int alive = ((icsk->icsk_rto << icsk->icsk_backoff) < TCP_RTO_MAX); + + max_probes = tcp_orphan_retries(sk, alive); + + if (tcp_out_of_resources(sk, alive || icsk->icsk_probes_out <= max_probes)) + return; + } + + if (icsk->icsk_probes_out > max_probes) { + tcp_write_err(sk); + } else { + /* Only send another probe if we didn't close things up. */ + tcp_send_probe0(sk); + } +} + +/* + * The TCP retransmit timer. + */ + +void tcp_retransmit_timer(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + struct inet_connection_sock *icsk = inet_csk(sk); + + if (!tp->packets_out) + goto out; + + WARN_ON(tcp_write_queue_empty(sk)); + + 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) { + LIMIT_NETDEBUG(KERN_DEBUG pr_fmt("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) { + struct ipv6_pinfo *np = inet6_sk(sk); + LIMIT_NETDEBUG(KERN_DEBUG pr_fmt("Peer %pI6:%u/%u unexpectedly shrunk window %u:%u (repaired)\n"), + &np->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, 0); + tcp_retransmit_skb(sk, tcp_write_queue_head(sk)); + __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_BH(sock_net(sk), mib_idx); + } + + if (tcp_use_frto(sk)) { + tcp_enter_frto(sk); + } else { + tcp_enter_loss(sk, 0); + } + + if (tcp_retransmit_skb(sk, tcp_write_queue_head(sk)) > 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, sysctl_tcp_retries1 + 1, 0, 0)) + __sk_dst_reset(sk); + +out:; +} + +static void tcp_write_timer(unsigned long data) +{ + struct sock *sk = (struct sock *)data; + struct inet_connection_sock *icsk = inet_csk(sk); + int event; + + bh_lock_sock(sk); + if (sock_owned_by_user(sk)) { + /* Try again later */ + sk_reset_timer(sk, &icsk->icsk_retransmit_timer, jiffies + (HZ / 20)); + goto out_unlock; + } + + 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; + icsk->icsk_pending = 0; + + switch (event) { + case ICSK_TIME_RETRANS: + tcp_retransmit_timer(sk); + break; + case ICSK_TIME_PROBE0: + tcp_probe_timer(sk); + break; + } + +out: + sk_mem_reclaim(sk); +out_unlock: + bh_unlock_sock(sk); + sock_put(sk); +} + +/* + * Timer for listening sockets + */ + +static void tcp_synack_timer(struct sock *sk) +{ + inet_csk_reqsk_queue_prune(sk, TCP_SYNQ_INTERVAL, + TCP_TIMEOUT_INIT, TCP_RTO_MAX); +} + +void tcp_syn_ack_timeout(struct sock *sk, struct request_sock *req) +{ + NET_INC_STATS_BH(sock_net(sk), 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) { + tcp_synack_timer(sk); + 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) <= 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); +} |