| /* |
| * 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/mm.h> |
| #include <linux/module.h> |
| #include <linux/slab.h> |
| #include <linux/sysctl.h> |
| #include <linux/workqueue.h> |
| #include <linux/static_key.h> |
| #include <net/tcp.h> |
| #include <net/inet_common.h> |
| #include <net/xfrm.h> |
| #include <net/busy_poll.h> |
| |
| static bool tcp_in_window(u32 seq, u32 end_seq, u32 s_win, u32 e_win) |
| { |
| if (seq == s_win) |
| return true; |
| if (after(end_seq, s_win) && before(seq, e_win)) |
| return true; |
| return seq == e_win && seq == end_seq; |
| } |
| |
| static enum tcp_tw_status |
| tcp_timewait_check_oow_rate_limit(struct inet_timewait_sock *tw, |
| const struct sk_buff *skb, int mib_idx) |
| { |
| struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); |
| |
| if (!tcp_oow_rate_limited(twsk_net(tw), skb, mib_idx, |
| &tcptw->tw_last_oow_ack_time)) { |
| /* Send ACK. Note, we do not put the bucket, |
| * it will be released by caller. |
| */ |
| return TCP_TW_ACK; |
| } |
| |
| /* We are rate-limiting, so just release the tw sock and drop skb. */ |
| inet_twsk_put(tw); |
| return TCP_TW_SUCCESS; |
| } |
| |
| /* |
| * * Main purpose of TIME-WAIT state is to close connection gracefully, |
| * when one of ends sits in LAST-ACK or CLOSING retransmitting FIN |
| * (and, probably, tail of data) and one or more our ACKs are lost. |
| * * What is TIME-WAIT timeout? It is associated with maximal packet |
| * lifetime in the internet, which results in wrong conclusion, that |
| * it is set to catch "old duplicate segments" wandering out of their path. |
| * It is not quite correct. This timeout is calculated so that it exceeds |
| * maximal retransmission timeout enough to allow to lose one (or more) |
| * segments sent by peer and our ACKs. This time may be calculated from RTO. |
| * * When TIME-WAIT socket receives RST, it means that another end |
| * finally closed and we are allowed to kill TIME-WAIT too. |
| * * Second purpose of TIME-WAIT is catching old duplicate segments. |
| * Well, certainly it is pure paranoia, but if we load TIME-WAIT |
| * with this semantics, we MUST NOT kill TIME-WAIT state with RSTs. |
| * * If we invented some more clever way to catch duplicates |
| * (f.e. based on PAWS), we could truncate TIME-WAIT to several RTOs. |
| * |
| * The algorithm below is based on FORMAL INTERPRETATION of RFCs. |
| * When you compare it to RFCs, please, read section SEGMENT ARRIVES |
| * from the very beginning. |
| * |
| * NOTE. With recycling (and later with fin-wait-2) TW bucket |
| * is _not_ stateless. It means, that strictly speaking we must |
| * spinlock it. I do not want! Well, probability of misbehaviour |
| * is ridiculously low and, seems, we could use some mb() tricks |
| * to avoid misread sequence numbers, states etc. --ANK |
| * |
| * We don't need to initialize tmp_out.sack_ok as we don't use the results |
| */ |
| enum tcp_tw_status |
| tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb, |
| const struct tcphdr *th) |
| { |
| struct tcp_options_received tmp_opt; |
| struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); |
| bool paws_reject = false; |
| |
| tmp_opt.saw_tstamp = 0; |
| if (th->doff > (sizeof(*th) >> 2) && tcptw->tw_ts_recent_stamp) { |
| tcp_parse_options(twsk_net(tw), skb, &tmp_opt, 0, NULL); |
| |
| if (tmp_opt.saw_tstamp) { |
| if (tmp_opt.rcv_tsecr) |
| tmp_opt.rcv_tsecr -= tcptw->tw_ts_offset; |
| tmp_opt.ts_recent = tcptw->tw_ts_recent; |
| tmp_opt.ts_recent_stamp = tcptw->tw_ts_recent_stamp; |
| paws_reject = tcp_paws_reject(&tmp_opt, th->rst); |
| } |
| } |
| |
| if (tw->tw_substate == TCP_FIN_WAIT2) { |
| /* Just repeat all the checks of tcp_rcv_state_process() */ |
| |
| /* Out of window, send ACK */ |
| if (paws_reject || |
| !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq, |
| tcptw->tw_rcv_nxt, |
| tcptw->tw_rcv_nxt + tcptw->tw_rcv_wnd)) |
| return tcp_timewait_check_oow_rate_limit( |
| tw, skb, LINUX_MIB_TCPACKSKIPPEDFINWAIT2); |
| |
| if (th->rst) |
| goto kill; |
| |
| if (th->syn && !before(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt)) |
| return TCP_TW_RST; |
| |
| /* Dup ACK? */ |
| if (!th->ack || |
| !after(TCP_SKB_CB(skb)->end_seq, tcptw->tw_rcv_nxt) || |
| TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq) { |
| inet_twsk_put(tw); |
| return TCP_TW_SUCCESS; |
| } |
| |
| /* New data or FIN. If new data arrive after half-duplex close, |
| * reset. |
| */ |
| if (!th->fin || |
| TCP_SKB_CB(skb)->end_seq != tcptw->tw_rcv_nxt + 1) |
| return TCP_TW_RST; |
| |
| /* FIN arrived, enter true time-wait state. */ |
| tw->tw_substate = TCP_TIME_WAIT; |
| tcptw->tw_rcv_nxt = TCP_SKB_CB(skb)->end_seq; |
| if (tmp_opt.saw_tstamp) { |
| tcptw->tw_ts_recent_stamp = ktime_get_seconds(); |
| tcptw->tw_ts_recent = tmp_opt.rcv_tsval; |
| } |
| |
| inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN); |
| return TCP_TW_ACK; |
| } |
| |
| /* |
| * Now real TIME-WAIT state. |
| * |
| * RFC 1122: |
| * "When a connection is [...] on TIME-WAIT state [...] |
| * [a TCP] MAY accept a new SYN from the remote TCP to |
| * reopen the connection directly, if it: |
| * |
| * (1) assigns its initial sequence number for the new |
| * connection to be larger than the largest sequence |
| * number it used on the previous connection incarnation, |
| * and |
| * |
| * (2) returns to TIME-WAIT state if the SYN turns out |
| * to be an old duplicate". |
| */ |
| |
| if (!paws_reject && |
| (TCP_SKB_CB(skb)->seq == tcptw->tw_rcv_nxt && |
| (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq || th->rst))) { |
| /* In window segment, it may be only reset or bare ack. */ |
| |
| if (th->rst) { |
| /* This is TIME_WAIT assassination, in two flavors. |
| * Oh well... nobody has a sufficient solution to this |
| * protocol bug yet. |
| */ |
| if (twsk_net(tw)->ipv4.sysctl_tcp_rfc1337 == 0) { |
| kill: |
| inet_twsk_deschedule_put(tw); |
| return TCP_TW_SUCCESS; |
| } |
| } else { |
| inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN); |
| } |
| |
| if (tmp_opt.saw_tstamp) { |
| tcptw->tw_ts_recent = tmp_opt.rcv_tsval; |
| tcptw->tw_ts_recent_stamp = ktime_get_seconds(); |
| } |
| |
| inet_twsk_put(tw); |
| return TCP_TW_SUCCESS; |
| } |
| |
| /* Out of window segment. |
| |
| All the segments are ACKed immediately. |
| |
| The only exception is new SYN. We accept it, if it is |
| not old duplicate and we are not in danger to be killed |
| by delayed old duplicates. RFC check is that it has |
| newer sequence number works at rates <40Mbit/sec. |
| However, if paws works, it is reliable AND even more, |
| we even may relax silly seq space cutoff. |
| |
| RED-PEN: we violate main RFC requirement, if this SYN will appear |
| old duplicate (i.e. we receive RST in reply to SYN-ACK), |
| we must return socket to time-wait state. It is not good, |
| but not fatal yet. |
| */ |
| |
| if (th->syn && !th->rst && !th->ack && !paws_reject && |
| (after(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt) || |
| (tmp_opt.saw_tstamp && |
| (s32)(tcptw->tw_ts_recent - tmp_opt.rcv_tsval) < 0))) { |
| u32 isn = tcptw->tw_snd_nxt + 65535 + 2; |
| if (isn == 0) |
| isn++; |
| TCP_SKB_CB(skb)->tcp_tw_isn = isn; |
| return TCP_TW_SYN; |
| } |
| |
| if (paws_reject) |
| __NET_INC_STATS(twsk_net(tw), LINUX_MIB_PAWSESTABREJECTED); |
| |
| if (!th->rst) { |
| /* In this case we must reset the TIMEWAIT timer. |
| * |
| * If it is ACKless SYN it may be both old duplicate |
| * and new good SYN with random sequence number <rcv_nxt. |
| * Do not reschedule in the last case. |
| */ |
| if (paws_reject || th->ack) |
| inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN); |
| |
| return tcp_timewait_check_oow_rate_limit( |
| tw, skb, LINUX_MIB_TCPACKSKIPPEDTIMEWAIT); |
| } |
| inet_twsk_put(tw); |
| return TCP_TW_SUCCESS; |
| } |
| EXPORT_SYMBOL(tcp_timewait_state_process); |
| |
| /* |
| * Move a socket to time-wait or dead fin-wait-2 state. |
| */ |
| void tcp_time_wait(struct sock *sk, int state, int timeo) |
| { |
| const struct inet_connection_sock *icsk = inet_csk(sk); |
| const struct tcp_sock *tp = tcp_sk(sk); |
| struct inet_timewait_sock *tw; |
| struct inet_timewait_death_row *tcp_death_row = &sock_net(sk)->ipv4.tcp_death_row; |
| |
| tw = inet_twsk_alloc(sk, tcp_death_row, state); |
| |
| if (tw) { |
| struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); |
| const int rto = (icsk->icsk_rto << 2) - (icsk->icsk_rto >> 1); |
| struct inet_sock *inet = inet_sk(sk); |
| |
| tw->tw_transparent = inet->transparent; |
| tw->tw_mark = sk->sk_mark; |
| tw->tw_rcv_wscale = tp->rx_opt.rcv_wscale; |
| tcptw->tw_rcv_nxt = tp->rcv_nxt; |
| tcptw->tw_snd_nxt = tp->snd_nxt; |
| tcptw->tw_rcv_wnd = tcp_receive_window(tp); |
| tcptw->tw_ts_recent = tp->rx_opt.ts_recent; |
| tcptw->tw_ts_recent_stamp = tp->rx_opt.ts_recent_stamp; |
| tcptw->tw_ts_offset = tp->tsoffset; |
| tcptw->tw_last_oow_ack_time = 0; |
| |
| #if IS_ENABLED(CONFIG_IPV6) |
| if (tw->tw_family == PF_INET6) { |
| struct ipv6_pinfo *np = inet6_sk(sk); |
| |
| tw->tw_v6_daddr = sk->sk_v6_daddr; |
| tw->tw_v6_rcv_saddr = sk->sk_v6_rcv_saddr; |
| tw->tw_tclass = np->tclass; |
| tw->tw_flowlabel = be32_to_cpu(np->flow_label & IPV6_FLOWLABEL_MASK); |
| tw->tw_ipv6only = sk->sk_ipv6only; |
| } |
| #endif |
| |
| #ifdef CONFIG_TCP_MD5SIG |
| /* |
| * The timewait bucket does not have the key DB from the |
| * sock structure. We just make a quick copy of the |
| * md5 key being used (if indeed we are using one) |
| * so the timewait ack generating code has the key. |
| */ |
| do { |
| tcptw->tw_md5_key = NULL; |
| if (static_branch_unlikely(&tcp_md5_needed)) { |
| struct tcp_md5sig_key *key; |
| |
| key = tp->af_specific->md5_lookup(sk, sk); |
| if (key) { |
| tcptw->tw_md5_key = kmemdup(key, sizeof(*key), GFP_ATOMIC); |
| BUG_ON(tcptw->tw_md5_key && !tcp_alloc_md5sig_pool()); |
| } |
| } |
| } while (0); |
| #endif |
| |
| /* Get the TIME_WAIT timeout firing. */ |
| if (timeo < rto) |
| timeo = rto; |
| |
| if (state == TCP_TIME_WAIT) |
| timeo = TCP_TIMEWAIT_LEN; |
| |
| /* tw_timer is pinned, so we need to make sure BH are disabled |
| * in following section, otherwise timer handler could run before |
| * we complete the initialization. |
| */ |
| local_bh_disable(); |
| inet_twsk_schedule(tw, timeo); |
| /* Linkage updates. |
| * Note that access to tw after this point is illegal. |
| */ |
| inet_twsk_hashdance(tw, sk, &tcp_hashinfo); |
| local_bh_enable(); |
| } else { |
| /* Sorry, if we're out of memory, just CLOSE this |
| * socket up. We've got bigger problems than |
| * non-graceful socket closings. |
| */ |
| NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPTIMEWAITOVERFLOW); |
| } |
| |
| tcp_update_metrics(sk); |
| tcp_done(sk); |
| } |
| EXPORT_SYMBOL(tcp_time_wait); |
| |
| void tcp_twsk_destructor(struct sock *sk) |
| { |
| #ifdef CONFIG_TCP_MD5SIG |
| if (static_branch_unlikely(&tcp_md5_needed)) { |
| struct tcp_timewait_sock *twsk = tcp_twsk(sk); |
| |
| if (twsk->tw_md5_key) |
| kfree_rcu(twsk->tw_md5_key, rcu); |
| } |
| #endif |
| } |
| EXPORT_SYMBOL_GPL(tcp_twsk_destructor); |
| |
| /* Warning : This function is called without sk_listener being locked. |
| * Be sure to read socket fields once, as their value could change under us. |
| */ |
| void tcp_openreq_init_rwin(struct request_sock *req, |
| const struct sock *sk_listener, |
| const struct dst_entry *dst) |
| { |
| struct inet_request_sock *ireq = inet_rsk(req); |
| const struct tcp_sock *tp = tcp_sk(sk_listener); |
| int full_space = tcp_full_space(sk_listener); |
| u32 window_clamp; |
| __u8 rcv_wscale; |
| u32 rcv_wnd; |
| int mss; |
| |
| mss = tcp_mss_clamp(tp, dst_metric_advmss(dst)); |
| window_clamp = READ_ONCE(tp->window_clamp); |
| /* Set this up on the first call only */ |
| req->rsk_window_clamp = window_clamp ? : dst_metric(dst, RTAX_WINDOW); |
| |
| /* limit the window selection if the user enforce a smaller rx buffer */ |
| if (sk_listener->sk_userlocks & SOCK_RCVBUF_LOCK && |
| (req->rsk_window_clamp > full_space || req->rsk_window_clamp == 0)) |
| req->rsk_window_clamp = full_space; |
| |
| rcv_wnd = tcp_rwnd_init_bpf((struct sock *)req); |
| if (rcv_wnd == 0) |
| rcv_wnd = dst_metric(dst, RTAX_INITRWND); |
| else if (full_space < rcv_wnd * mss) |
| full_space = rcv_wnd * mss; |
| |
| /* tcp_full_space because it is guaranteed to be the first packet */ |
| tcp_select_initial_window(sk_listener, full_space, |
| mss - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0), |
| &req->rsk_rcv_wnd, |
| &req->rsk_window_clamp, |
| ireq->wscale_ok, |
| &rcv_wscale, |
| rcv_wnd); |
| ireq->rcv_wscale = rcv_wscale; |
| } |
| EXPORT_SYMBOL(tcp_openreq_init_rwin); |
| |
| static void tcp_ecn_openreq_child(struct tcp_sock *tp, |
| const struct request_sock *req) |
| { |
| tp->ecn_flags = inet_rsk(req)->ecn_ok ? TCP_ECN_OK : 0; |
| } |
| |
| void tcp_ca_openreq_child(struct sock *sk, const struct dst_entry *dst) |
| { |
| struct inet_connection_sock *icsk = inet_csk(sk); |
| u32 ca_key = dst_metric(dst, RTAX_CC_ALGO); |
| bool ca_got_dst = false; |
| |
| if (ca_key != TCP_CA_UNSPEC) { |
| const struct tcp_congestion_ops *ca; |
| |
| rcu_read_lock(); |
| ca = tcp_ca_find_key(ca_key); |
| if (likely(ca && try_module_get(ca->owner))) { |
| icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst); |
| icsk->icsk_ca_ops = ca; |
| ca_got_dst = true; |
| } |
| rcu_read_unlock(); |
| } |
| |
| /* If no valid choice made yet, assign current system default ca. */ |
| if (!ca_got_dst && |
| (!icsk->icsk_ca_setsockopt || |
| !try_module_get(icsk->icsk_ca_ops->owner))) |
| tcp_assign_congestion_control(sk); |
| |
| tcp_set_ca_state(sk, TCP_CA_Open); |
| } |
| EXPORT_SYMBOL_GPL(tcp_ca_openreq_child); |
| |
| static void smc_check_reset_syn_req(struct tcp_sock *oldtp, |
| struct request_sock *req, |
| struct tcp_sock *newtp) |
| { |
| #if IS_ENABLED(CONFIG_SMC) |
| struct inet_request_sock *ireq; |
| |
| if (static_branch_unlikely(&tcp_have_smc)) { |
| ireq = inet_rsk(req); |
| if (oldtp->syn_smc && !ireq->smc_ok) |
| newtp->syn_smc = 0; |
| } |
| #endif |
| } |
| |
| /* This is not only more efficient than what we used to do, it eliminates |
| * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM |
| * |
| * Actually, we could lots of memory writes here. tp of listening |
| * socket contains all necessary default parameters. |
| */ |
| struct sock *tcp_create_openreq_child(const struct sock *sk, |
| struct request_sock *req, |
| struct sk_buff *skb) |
| { |
| struct sock *newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC); |
| const struct inet_request_sock *ireq = inet_rsk(req); |
| struct tcp_request_sock *treq = tcp_rsk(req); |
| struct inet_connection_sock *newicsk; |
| struct tcp_sock *oldtp, *newtp; |
| |
| if (!newsk) |
| return NULL; |
| |
| newicsk = inet_csk(newsk); |
| newtp = tcp_sk(newsk); |
| oldtp = tcp_sk(sk); |
| |
| smc_check_reset_syn_req(oldtp, req, newtp); |
| |
| /* Now setup tcp_sock */ |
| newtp->pred_flags = 0; |
| |
| newtp->rcv_wup = newtp->copied_seq = |
| newtp->rcv_nxt = treq->rcv_isn + 1; |
| newtp->segs_in = 1; |
| |
| newtp->snd_sml = newtp->snd_una = |
| newtp->snd_nxt = newtp->snd_up = treq->snt_isn + 1; |
| |
| INIT_LIST_HEAD(&newtp->tsq_node); |
| INIT_LIST_HEAD(&newtp->tsorted_sent_queue); |
| |
| tcp_init_wl(newtp, treq->rcv_isn); |
| |
| minmax_reset(&newtp->rtt_min, tcp_jiffies32, ~0U); |
| newicsk->icsk_ack.lrcvtime = tcp_jiffies32; |
| |
| newtp->lsndtime = tcp_jiffies32; |
| newsk->sk_txhash = treq->txhash; |
| newtp->total_retrans = req->num_retrans; |
| |
| tcp_init_xmit_timers(newsk); |
| newtp->write_seq = newtp->pushed_seq = treq->snt_isn + 1; |
| |
| if (sock_flag(newsk, SOCK_KEEPOPEN)) |
| inet_csk_reset_keepalive_timer(newsk, |
| keepalive_time_when(newtp)); |
| |
| newtp->rx_opt.tstamp_ok = ireq->tstamp_ok; |
| newtp->rx_opt.sack_ok = ireq->sack_ok; |
| newtp->window_clamp = req->rsk_window_clamp; |
| newtp->rcv_ssthresh = req->rsk_rcv_wnd; |
| newtp->rcv_wnd = req->rsk_rcv_wnd; |
| newtp->rx_opt.wscale_ok = ireq->wscale_ok; |
| if (newtp->rx_opt.wscale_ok) { |
| newtp->rx_opt.snd_wscale = ireq->snd_wscale; |
| newtp->rx_opt.rcv_wscale = ireq->rcv_wscale; |
| } else { |
| newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0; |
| newtp->window_clamp = min(newtp->window_clamp, 65535U); |
| } |
| newtp->snd_wnd = ntohs(tcp_hdr(skb)->window) << newtp->rx_opt.snd_wscale; |
| newtp->max_window = newtp->snd_wnd; |
| |
| if (newtp->rx_opt.tstamp_ok) { |
| newtp->rx_opt.ts_recent = req->ts_recent; |
| newtp->rx_opt.ts_recent_stamp = ktime_get_seconds(); |
| newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED; |
| } else { |
| newtp->rx_opt.ts_recent_stamp = 0; |
| newtp->tcp_header_len = sizeof(struct tcphdr); |
| } |
| if (req->num_timeout) { |
| newtp->undo_marker = treq->snt_isn; |
| newtp->retrans_stamp = div_u64(treq->snt_synack, |
| USEC_PER_SEC / TCP_TS_HZ); |
| } |
| newtp->tsoffset = treq->ts_off; |
| #ifdef CONFIG_TCP_MD5SIG |
| newtp->md5sig_info = NULL; /*XXX*/ |
| if (newtp->af_specific->md5_lookup(sk, newsk)) |
| newtp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED; |
| #endif |
| if (skb->len >= TCP_MSS_DEFAULT + newtp->tcp_header_len) |
| newicsk->icsk_ack.last_seg_size = skb->len - newtp->tcp_header_len; |
| newtp->rx_opt.mss_clamp = req->mss; |
| tcp_ecn_openreq_child(newtp, req); |
| newtp->fastopen_req = NULL; |
| newtp->fastopen_rsk = NULL; |
| |
| __TCP_INC_STATS(sock_net(sk), TCP_MIB_PASSIVEOPENS); |
| |
| return newsk; |
| } |
| EXPORT_SYMBOL(tcp_create_openreq_child); |
| |
| /* |
| * Process an incoming packet for SYN_RECV sockets represented as a |
| * request_sock. Normally sk is the listener socket but for TFO it |
| * points to the child socket. |
| * |
| * XXX (TFO) - The current impl contains a special check for ack |
| * validation and inside tcp_v4_reqsk_send_ack(). Can we do better? |
| * |
| * We don't need to initialize tmp_opt.sack_ok as we don't use the results |
| */ |
| |
| struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb, |
| struct request_sock *req, |
| bool fastopen, bool *req_stolen) |
| { |
| struct tcp_options_received tmp_opt; |
| struct sock *child; |
| const struct tcphdr *th = tcp_hdr(skb); |
| __be32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK); |
| bool paws_reject = false; |
| bool own_req; |
| |
| tmp_opt.saw_tstamp = 0; |
| if (th->doff > (sizeof(struct tcphdr)>>2)) { |
| tcp_parse_options(sock_net(sk), skb, &tmp_opt, 0, NULL); |
| |
| if (tmp_opt.saw_tstamp) { |
| tmp_opt.ts_recent = req->ts_recent; |
| if (tmp_opt.rcv_tsecr) |
| tmp_opt.rcv_tsecr -= tcp_rsk(req)->ts_off; |
| /* We do not store true stamp, but it is not required, |
| * it can be estimated (approximately) |
| * from another data. |
| */ |
| tmp_opt.ts_recent_stamp = ktime_get_seconds() - ((TCP_TIMEOUT_INIT/HZ)<<req->num_timeout); |
| paws_reject = tcp_paws_reject(&tmp_opt, th->rst); |
| } |
| } |
| |
| /* Check for pure retransmitted SYN. */ |
| if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn && |
| flg == TCP_FLAG_SYN && |
| !paws_reject) { |
| /* |
| * RFC793 draws (Incorrectly! It was fixed in RFC1122) |
| * this case on figure 6 and figure 8, but formal |
| * protocol description says NOTHING. |
| * To be more exact, it says that we should send ACK, |
| * because this segment (at least, if it has no data) |
| * is out of window. |
| * |
| * CONCLUSION: RFC793 (even with RFC1122) DOES NOT |
| * describe SYN-RECV state. All the description |
| * is wrong, we cannot believe to it and should |
| * rely only on common sense and implementation |
| * experience. |
| * |
| * Enforce "SYN-ACK" according to figure 8, figure 6 |
| * of RFC793, fixed by RFC1122. |
| * |
| * Note that even if there is new data in the SYN packet |
| * they will be thrown away too. |
| * |
| * Reset timer after retransmitting SYNACK, similar to |
| * the idea of fast retransmit in recovery. |
| */ |
| if (!tcp_oow_rate_limited(sock_net(sk), skb, |
| LINUX_MIB_TCPACKSKIPPEDSYNRECV, |
| &tcp_rsk(req)->last_oow_ack_time) && |
| |
| !inet_rtx_syn_ack(sk, req)) { |
| unsigned long expires = jiffies; |
| |
| expires += min(TCP_TIMEOUT_INIT << req->num_timeout, |
| TCP_RTO_MAX); |
| if (!fastopen) |
| mod_timer_pending(&req->rsk_timer, expires); |
| else |
| req->rsk_timer.expires = expires; |
| } |
| return NULL; |
| } |
| |
| /* Further reproduces section "SEGMENT ARRIVES" |
| for state SYN-RECEIVED of RFC793. |
| It is broken, however, it does not work only |
| when SYNs are crossed. |
| |
| You would think that SYN crossing is impossible here, since |
| we should have a SYN_SENT socket (from connect()) on our end, |
| but this is not true if the crossed SYNs were sent to both |
| ends by a malicious third party. We must defend against this, |
| and to do that we first verify the ACK (as per RFC793, page |
| 36) and reset if it is invalid. Is this a true full defense? |
| To convince ourselves, let us consider a way in which the ACK |
| test can still pass in this 'malicious crossed SYNs' case. |
| Malicious sender sends identical SYNs (and thus identical sequence |
| numbers) to both A and B: |
| |
| A: gets SYN, seq=7 |
| B: gets SYN, seq=7 |
| |
| By our good fortune, both A and B select the same initial |
| send sequence number of seven :-) |
| |
| A: sends SYN|ACK, seq=7, ack_seq=8 |
| B: sends SYN|ACK, seq=7, ack_seq=8 |
| |
| So we are now A eating this SYN|ACK, ACK test passes. So |
| does sequence test, SYN is truncated, and thus we consider |
| it a bare ACK. |
| |
| If icsk->icsk_accept_queue.rskq_defer_accept, we silently drop this |
| bare ACK. Otherwise, we create an established connection. Both |
| ends (listening sockets) accept the new incoming connection and try |
| to talk to each other. 8-) |
| |
| Note: This case is both harmless, and rare. Possibility is about the |
| same as us discovering intelligent life on another plant tomorrow. |
| |
| But generally, we should (RFC lies!) to accept ACK |
| from SYNACK both here and in tcp_rcv_state_process(). |
| tcp_rcv_state_process() does not, hence, we do not too. |
| |
| Note that the case is absolutely generic: |
| we cannot optimize anything here without |
| violating protocol. All the checks must be made |
| before attempt to create socket. |
| */ |
| |
| /* RFC793 page 36: "If the connection is in any non-synchronized state ... |
| * and the incoming segment acknowledges something not yet |
| * sent (the segment carries an unacceptable ACK) ... |
| * a reset is sent." |
| * |
| * Invalid ACK: reset will be sent by listening socket. |
| * Note that the ACK validity check for a Fast Open socket is done |
| * elsewhere and is checked directly against the child socket rather |
| * than req because user data may have been sent out. |
| */ |
| if ((flg & TCP_FLAG_ACK) && !fastopen && |
| (TCP_SKB_CB(skb)->ack_seq != |
| tcp_rsk(req)->snt_isn + 1)) |
| return sk; |
| |
| /* Also, it would be not so bad idea to check rcv_tsecr, which |
| * is essentially ACK extension and too early or too late values |
| * should cause reset in unsynchronized states. |
| */ |
| |
| /* RFC793: "first check sequence number". */ |
| |
| if (paws_reject || !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq, |
| tcp_rsk(req)->rcv_nxt, tcp_rsk(req)->rcv_nxt + req->rsk_rcv_wnd)) { |
| /* Out of window: send ACK and drop. */ |
| if (!(flg & TCP_FLAG_RST) && |
| !tcp_oow_rate_limited(sock_net(sk), skb, |
| LINUX_MIB_TCPACKSKIPPEDSYNRECV, |
| &tcp_rsk(req)->last_oow_ack_time)) |
| req->rsk_ops->send_ack(sk, skb, req); |
| if (paws_reject) |
| __NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED); |
| return NULL; |
| } |
| |
| /* In sequence, PAWS is OK. */ |
| |
| if (tmp_opt.saw_tstamp && !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_nxt)) |
| req->ts_recent = tmp_opt.rcv_tsval; |
| |
| if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) { |
| /* Truncate SYN, it is out of window starting |
| at tcp_rsk(req)->rcv_isn + 1. */ |
| flg &= ~TCP_FLAG_SYN; |
| } |
| |
| /* RFC793: "second check the RST bit" and |
| * "fourth, check the SYN bit" |
| */ |
| if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) { |
| __TCP_INC_STATS(sock_net(sk), TCP_MIB_ATTEMPTFAILS); |
| goto embryonic_reset; |
| } |
| |
| /* ACK sequence verified above, just make sure ACK is |
| * set. If ACK not set, just silently drop the packet. |
| * |
| * XXX (TFO) - if we ever allow "data after SYN", the |
| * following check needs to be removed. |
| */ |
| if (!(flg & TCP_FLAG_ACK)) |
| return NULL; |
| |
| /* For Fast Open no more processing is needed (sk is the |
| * child socket). |
| */ |
| if (fastopen) |
| return sk; |
| |
| /* While TCP_DEFER_ACCEPT is active, drop bare ACK. */ |
| if (req->num_timeout < inet_csk(sk)->icsk_accept_queue.rskq_defer_accept && |
| TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) { |
| inet_rsk(req)->acked = 1; |
| __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP); |
| return NULL; |
| } |
| |
| /* OK, ACK is valid, create big socket and |
| * feed this segment to it. It will repeat all |
| * the tests. THIS SEGMENT MUST MOVE SOCKET TO |
| * ESTABLISHED STATE. If it will be dropped after |
| * socket is created, wait for troubles. |
| */ |
| child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL, |
| req, &own_req); |
| if (!child) |
| goto listen_overflow; |
| |
| sock_rps_save_rxhash(child, skb); |
| tcp_synack_rtt_meas(child, req); |
| *req_stolen = !own_req; |
| return inet_csk_complete_hashdance(sk, child, req, own_req); |
| |
| listen_overflow: |
| if (!sock_net(sk)->ipv4.sysctl_tcp_abort_on_overflow) { |
| inet_rsk(req)->acked = 1; |
| return NULL; |
| } |
| |
| embryonic_reset: |
| if (!(flg & TCP_FLAG_RST)) { |
| /* Received a bad SYN pkt - for TFO We try not to reset |
| * the local connection unless it's really necessary to |
| * avoid becoming vulnerable to outside attack aiming at |
| * resetting legit local connections. |
| */ |
| req->rsk_ops->send_reset(sk, skb); |
| } else if (fastopen) { /* received a valid RST pkt */ |
| reqsk_fastopen_remove(sk, req, true); |
| tcp_reset(sk); |
| } |
| if (!fastopen) { |
| inet_csk_reqsk_queue_drop(sk, req); |
| __NET_INC_STATS(sock_net(sk), LINUX_MIB_EMBRYONICRSTS); |
| } |
| return NULL; |
| } |
| EXPORT_SYMBOL(tcp_check_req); |
| |
| /* |
| * Queue segment on the new socket if the new socket is active, |
| * otherwise we just shortcircuit this and continue with |
| * the new socket. |
| * |
| * For the vast majority of cases child->sk_state will be TCP_SYN_RECV |
| * when entering. But other states are possible due to a race condition |
| * where after __inet_lookup_established() fails but before the listener |
| * locked is obtained, other packets cause the same connection to |
| * be created. |
| */ |
| |
| int tcp_child_process(struct sock *parent, struct sock *child, |
| struct sk_buff *skb) |
| { |
| int ret = 0; |
| int state = child->sk_state; |
| |
| /* record NAPI ID of child */ |
| sk_mark_napi_id(child, skb); |
| |
| tcp_segs_in(tcp_sk(child), skb); |
| if (!sock_owned_by_user(child)) { |
| ret = tcp_rcv_state_process(child, skb); |
| /* Wakeup parent, send SIGIO */ |
| if (state == TCP_SYN_RECV && child->sk_state != state) |
| parent->sk_data_ready(parent); |
| } else { |
| /* Alas, it is possible again, because we do lookup |
| * in main socket hash table and lock on listening |
| * socket does not protect us more. |
| */ |
| __sk_add_backlog(child, skb); |
| } |
| |
| bh_unlock_sock(child); |
| sock_put(child); |
| return ret; |
| } |
| EXPORT_SYMBOL(tcp_child_process); |