--- /dev/null
+/*
+ * 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 <net/tcp.h>
+#include <net/inet_common.h>
+#include <net/xfrm.h>
+
+int sysctl_tcp_syncookies __read_mostly = 1;
+EXPORT_SYMBOL(sysctl_tcp_syncookies);
+
+int sysctl_tcp_abort_on_overflow __read_mostly;
+
+struct inet_timewait_death_row tcp_death_row = {
+ .sysctl_max_tw_buckets = NR_FILE * 2,
+ .hashinfo = &tcp_hashinfo,
+};
+EXPORT_SYMBOL_GPL(tcp_death_row);
+
+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(skb, &tmp_opt, 0, NULL);
+
+ if (tmp_opt.saw_tstamp) {
+ 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))
+ goto kill_with_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) {
+kill_with_rst:
+ inet_twsk_deschedule(tw);
+ inet_twsk_put(tw);
+ 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 = get_seconds();
+ tcptw->tw_ts_recent = tmp_opt.rcv_tsval;
+ }
+
+ if (tcp_death_row.sysctl_tw_recycle &&
+ tcptw->tw_ts_recent_stamp &&
+ tcp_tw_remember_stamp(tw))
+ inet_twsk_schedule(tw, tw->tw_timeout);
+ else
+ inet_twsk_schedule(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 (sysctl_tcp_rfc1337 == 0) {
+kill:
+ inet_twsk_deschedule(tw);
+ inet_twsk_put(tw);
+ return TCP_TW_SUCCESS;
+ }
+ }
+ inet_twsk_schedule(tw, TCP_TIMEWAIT_LEN);
+
+ if (tmp_opt.saw_tstamp) {
+ tcptw->tw_ts_recent = tmp_opt.rcv_tsval;
+ tcptw->tw_ts_recent_stamp = 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_BH(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_schedule(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;
+ bool recycle_ok = false;
+
+ if (tcp_death_row.sysctl_tw_recycle && tp->rx_opt.ts_recent_stamp)
+ recycle_ok = tcp_remember_stamp(sk);
+
+ 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_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 {
+ struct tcp_md5sig_key *key;
+ tcptw->tw_md5_key = NULL;
+ key = tp->af_specific->md5_lookup(sk, sk);
+ if (key) {
+ tcptw->tw_md5_key = kmemdup(key, sizeof(*key), GFP_ATOMIC);
+ if (tcptw->tw_md5_key && !tcp_alloc_md5sig_pool())
+ BUG();
+ }
+ } while (0);
+#endif
+
+ /* Linkage updates. */
+ __inet_twsk_hashdance(tw, sk, &tcp_hashinfo);
+
+ /* Get the TIME_WAIT timeout firing. */
+ if (timeo < rto)
+ timeo = rto;
+
+ if (recycle_ok) {
+ tw->tw_timeout = rto;
+ } else {
+ tw->tw_timeout = TCP_TIMEWAIT_LEN;
+ if (state == TCP_TIME_WAIT)
+ timeo = TCP_TIMEWAIT_LEN;
+ }
+
+ inet_twsk_schedule(tw, timeo);
+ inet_twsk_put(tw);
+ } 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_BH(sock_net(sk), LINUX_MIB_TCPTIMEWAITOVERFLOW);
+ }
+
+ tcp_update_metrics(sk);
+ tcp_done(sk);
+}
+
+void tcp_twsk_destructor(struct sock *sk)
+{
+#ifdef CONFIG_TCP_MD5SIG
+ 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);
+
+void tcp_openreq_init_rwin(struct request_sock *req,
+ struct sock *sk, struct dst_entry *dst)
+{
+ struct inet_request_sock *ireq = inet_rsk(req);
+ struct tcp_sock *tp = tcp_sk(sk);
+ __u8 rcv_wscale;
+ int mss = dst_metric_advmss(dst);
+
+ if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < mss)
+ mss = tp->rx_opt.user_mss;
+
+ /* Set this up on the first call only */
+ req->window_clamp = tp->window_clamp ? : dst_metric(dst, RTAX_WINDOW);
+
+ /* limit the window selection if the user enforce a smaller rx buffer */
+ if (sk->sk_userlocks & SOCK_RCVBUF_LOCK &&
+ (req->window_clamp > tcp_full_space(sk) || req->window_clamp == 0))
+ req->window_clamp = tcp_full_space(sk);
+
+ /* tcp_full_space because it is guaranteed to be the first packet */
+ tcp_select_initial_window(tcp_full_space(sk),
+ mss - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0),
+ &req->rcv_wnd,
+ &req->window_clamp,
+ ireq->wscale_ok,
+ &rcv_wscale,
+ dst_metric(dst, RTAX_INITRWND));
+ 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);
+
+/* 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(struct sock *sk, struct request_sock *req, struct sk_buff *skb)
+{
+ struct sock *newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC);
+
+ if (newsk) {
+ const struct inet_request_sock *ireq = inet_rsk(req);
+ struct tcp_request_sock *treq = tcp_rsk(req);
+ struct inet_connection_sock *newicsk = inet_csk(newsk);
+ struct tcp_sock *newtp = tcp_sk(newsk);
+
+ /* Now setup tcp_sock */
+ newtp->pred_flags = 0;
+
+ newtp->rcv_wup = newtp->copied_seq =
+ newtp->rcv_nxt = treq->rcv_isn + 1;
+
+ newtp->snd_sml = newtp->snd_una =
+ newtp->snd_nxt = newtp->snd_up = treq->snt_isn + 1;
+
+ tcp_prequeue_init(newtp);
+ INIT_LIST_HEAD(&newtp->tsq_node);
+
+ tcp_init_wl(newtp, treq->rcv_isn);
+
+ newtp->srtt_us = 0;
+ newtp->mdev_us = jiffies_to_usecs(TCP_TIMEOUT_INIT);
+ newicsk->icsk_rto = TCP_TIMEOUT_INIT;
+
+ newtp->packets_out = 0;
+ newtp->retrans_out = 0;
+ newtp->sacked_out = 0;
+ newtp->fackets_out = 0;
+ newtp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
+ tcp_enable_early_retrans(newtp);
+ newtp->tlp_high_seq = 0;
+ newtp->lsndtime = treq->snt_synack;
+ newtp->last_oow_ack_time = 0;
+ newtp->total_retrans = req->num_retrans;
+
+ /* So many TCP implementations out there (incorrectly) count the
+ * initial SYN frame in their delayed-ACK and congestion control
+ * algorithms that we must have the following bandaid to talk
+ * efficiently to them. -DaveM
+ */
+ newtp->snd_cwnd = TCP_INIT_CWND;
+ newtp->snd_cwnd_cnt = 0;
+
+ tcp_init_xmit_timers(newsk);
+ __skb_queue_head_init(&newtp->out_of_order_queue);
+ newtp->write_seq = newtp->pushed_seq = treq->snt_isn + 1;
+
+ newtp->rx_opt.saw_tstamp = 0;
+
+ newtp->rx_opt.dsack = 0;
+ newtp->rx_opt.num_sacks = 0;
+
+ newtp->urg_data = 0;
+
+ if (sock_flag(newsk, SOCK_KEEPOPEN))
+ inet_csk_reset_keepalive_timer(newsk,
+ keepalive_time_when(newtp));
+
+ newtp->rx_opt.tstamp_ok = ireq->tstamp_ok;
+ if ((newtp->rx_opt.sack_ok = ireq->sack_ok) != 0) {
+ if (sysctl_tcp_fack)
+ tcp_enable_fack(newtp);
+ }
+ newtp->window_clamp = req->window_clamp;
+ newtp->rcv_ssthresh = req->rcv_wnd;
+ newtp->rcv_wnd = req->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 = 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);
+ }
+ newtp->tsoffset = 0;
+#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_rsk = NULL;
+ newtp->syn_data_acked = 0;
+
+ TCP_INC_STATS_BH(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)
+{
+ 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;
+
+ BUG_ON(fastopen == (sk->sk_state == TCP_LISTEN));
+
+ tmp_opt.saw_tstamp = 0;
+ if (th->doff > (sizeof(struct tcphdr)>>2)) {
+ tcp_parse_options(skb, &tmp_opt, 0, NULL);
+
+ if (tmp_opt.saw_tstamp) {
+ tmp_opt.ts_recent = req->ts_recent;
+ /* We do not store true stamp, but it is not required,
+ * it can be estimated (approximately)
+ * from another data.
+ */
+ tmp_opt.ts_recent_stamp = 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->rcv_wnd)) {
+ /* Out of window: send ACK and drop. */
+ if (!(flg & TCP_FLAG_RST))
+ req->rsk_ops->send_ack(sk, skb, req);
+ if (paws_reject)
+ NET_INC_STATS_BH(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_BH(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_BH(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);
+ if (!child)
+ goto listen_overflow;
+
+ inet_csk_reqsk_queue_drop(sk, req);
+ inet_csk_reqsk_queue_add(sk, req, child);
+ /* Warning: caller must not call reqsk_put(req);
+ * child stole last reference on it.
+ */
+ return child;
+
+listen_overflow:
+ if (!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_BH(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;
+
+ if (!sock_owned_by_user(child)) {
+ ret = tcp_rcv_state_process(child, skb, tcp_hdr(skb),
+ skb->len);
+ /* 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);
Code Review / kvmfornfv.git / blobdiff