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738 lines
23 KiB
738 lines
23 KiB
/*
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* INET An implementation of the TCP/IP protocol suite for the LINUX
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* operating system. INET is implemented using the BSD Socket
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* interface as the means of communication with the user level.
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*
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* Implementation of the Transmission Control Protocol(TCP).
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*
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* Authors: Ross Biro
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* Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
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* Mark Evans, <evansmp@uhura.aston.ac.uk>
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* Corey Minyard <wf-rch!minyard@relay.EU.net>
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* Florian La Roche, <flla@stud.uni-sb.de>
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* Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
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* Linus Torvalds, <torvalds@cs.helsinki.fi>
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* Alan Cox, <gw4pts@gw4pts.ampr.org>
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* Matthew Dillon, <dillon@apollo.west.oic.com>
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* Arnt Gulbrandsen, <agulbra@nvg.unit.no>
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* Jorge Cwik, <jorge@laser.satlink.net>
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*/
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#include <linux/mm.h>
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#include <linux/module.h>
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#include <linux/sysctl.h>
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#include <linux/workqueue.h>
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#include <net/tcp.h>
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#include <net/inet_common.h>
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#include <net/xfrm.h>
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#ifdef CONFIG_SYSCTL
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#define SYNC_INIT 0 /* let the user enable it */
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#else
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#define SYNC_INIT 1
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#endif
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int sysctl_tcp_syncookies __read_mostly = SYNC_INIT;
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EXPORT_SYMBOL(sysctl_tcp_syncookies);
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int sysctl_tcp_abort_on_overflow __read_mostly;
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struct inet_timewait_death_row tcp_death_row = {
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.sysctl_max_tw_buckets = NR_FILE * 2,
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.period = TCP_TIMEWAIT_LEN / INET_TWDR_TWKILL_SLOTS,
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.death_lock = __SPIN_LOCK_UNLOCKED(tcp_death_row.death_lock),
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.hashinfo = &tcp_hashinfo,
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.tw_timer = TIMER_INITIALIZER(inet_twdr_hangman, 0,
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(unsigned long)&tcp_death_row),
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.twkill_work = __WORK_INITIALIZER(tcp_death_row.twkill_work,
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inet_twdr_twkill_work),
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/* Short-time timewait calendar */
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.twcal_hand = -1,
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.twcal_timer = TIMER_INITIALIZER(inet_twdr_twcal_tick, 0,
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(unsigned long)&tcp_death_row),
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};
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EXPORT_SYMBOL_GPL(tcp_death_row);
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static __inline__ int tcp_in_window(u32 seq, u32 end_seq, u32 s_win, u32 e_win)
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{
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if (seq == s_win)
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return 1;
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if (after(end_seq, s_win) && before(seq, e_win))
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return 1;
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return (seq == e_win && seq == end_seq);
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}
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/*
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* * Main purpose of TIME-WAIT state is to close connection gracefully,
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* when one of ends sits in LAST-ACK or CLOSING retransmitting FIN
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* (and, probably, tail of data) and one or more our ACKs are lost.
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* * What is TIME-WAIT timeout? It is associated with maximal packet
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* lifetime in the internet, which results in wrong conclusion, that
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* it is set to catch "old duplicate segments" wandering out of their path.
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* It is not quite correct. This timeout is calculated so that it exceeds
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* maximal retransmission timeout enough to allow to lose one (or more)
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* segments sent by peer and our ACKs. This time may be calculated from RTO.
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* * When TIME-WAIT socket receives RST, it means that another end
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* finally closed and we are allowed to kill TIME-WAIT too.
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* * Second purpose of TIME-WAIT is catching old duplicate segments.
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* Well, certainly it is pure paranoia, but if we load TIME-WAIT
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* with this semantics, we MUST NOT kill TIME-WAIT state with RSTs.
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* * If we invented some more clever way to catch duplicates
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* (f.e. based on PAWS), we could truncate TIME-WAIT to several RTOs.
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*
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* The algorithm below is based on FORMAL INTERPRETATION of RFCs.
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* When you compare it to RFCs, please, read section SEGMENT ARRIVES
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* from the very beginning.
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*
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* NOTE. With recycling (and later with fin-wait-2) TW bucket
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* is _not_ stateless. It means, that strictly speaking we must
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* spinlock it. I do not want! Well, probability of misbehaviour
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* is ridiculously low and, seems, we could use some mb() tricks
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* to avoid misread sequence numbers, states etc. --ANK
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*/
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enum tcp_tw_status
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tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb,
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const struct tcphdr *th)
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{
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struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
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struct tcp_options_received tmp_opt;
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int paws_reject = 0;
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tmp_opt.saw_tstamp = 0;
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if (th->doff > (sizeof(*th) >> 2) && tcptw->tw_ts_recent_stamp) {
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tcp_parse_options(skb, &tmp_opt, 0);
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if (tmp_opt.saw_tstamp) {
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tmp_opt.ts_recent = tcptw->tw_ts_recent;
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tmp_opt.ts_recent_stamp = tcptw->tw_ts_recent_stamp;
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paws_reject = tcp_paws_reject(&tmp_opt, th->rst);
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}
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}
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if (tw->tw_substate == TCP_FIN_WAIT2) {
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/* Just repeat all the checks of tcp_rcv_state_process() */
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/* Out of window, send ACK */
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if (paws_reject ||
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!tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
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tcptw->tw_rcv_nxt,
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tcptw->tw_rcv_nxt + tcptw->tw_rcv_wnd))
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return TCP_TW_ACK;
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if (th->rst)
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goto kill;
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if (th->syn && !before(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt))
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goto kill_with_rst;
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/* Dup ACK? */
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if (!after(TCP_SKB_CB(skb)->end_seq, tcptw->tw_rcv_nxt) ||
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TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq) {
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inet_twsk_put(tw);
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return TCP_TW_SUCCESS;
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}
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/* New data or FIN. If new data arrive after half-duplex close,
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* reset.
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*/
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if (!th->fin ||
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TCP_SKB_CB(skb)->end_seq != tcptw->tw_rcv_nxt + 1) {
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kill_with_rst:
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inet_twsk_deschedule(tw, &tcp_death_row);
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inet_twsk_put(tw);
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return TCP_TW_RST;
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}
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/* FIN arrived, enter true time-wait state. */
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tw->tw_substate = TCP_TIME_WAIT;
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tcptw->tw_rcv_nxt = TCP_SKB_CB(skb)->end_seq;
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if (tmp_opt.saw_tstamp) {
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tcptw->tw_ts_recent_stamp = get_seconds();
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tcptw->tw_ts_recent = tmp_opt.rcv_tsval;
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}
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/* I am shamed, but failed to make it more elegant.
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* Yes, it is direct reference to IP, which is impossible
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* to generalize to IPv6. Taking into account that IPv6
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* do not understand recycling in any case, it not
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* a big problem in practice. --ANK */
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if (tw->tw_family == AF_INET &&
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tcp_death_row.sysctl_tw_recycle && tcptw->tw_ts_recent_stamp &&
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tcp_v4_tw_remember_stamp(tw))
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inet_twsk_schedule(tw, &tcp_death_row, tw->tw_timeout,
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TCP_TIMEWAIT_LEN);
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else
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inet_twsk_schedule(tw, &tcp_death_row, TCP_TIMEWAIT_LEN,
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TCP_TIMEWAIT_LEN);
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return TCP_TW_ACK;
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}
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/*
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* Now real TIME-WAIT state.
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*
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* RFC 1122:
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* "When a connection is [...] on TIME-WAIT state [...]
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* [a TCP] MAY accept a new SYN from the remote TCP to
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* reopen the connection directly, if it:
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*
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* (1) assigns its initial sequence number for the new
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* connection to be larger than the largest sequence
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* number it used on the previous connection incarnation,
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* and
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*
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* (2) returns to TIME-WAIT state if the SYN turns out
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* to be an old duplicate".
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*/
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if (!paws_reject &&
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(TCP_SKB_CB(skb)->seq == tcptw->tw_rcv_nxt &&
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(TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq || th->rst))) {
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/* In window segment, it may be only reset or bare ack. */
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if (th->rst) {
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/* This is TIME_WAIT assassination, in two flavors.
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* Oh well... nobody has a sufficient solution to this
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* protocol bug yet.
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*/
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if (sysctl_tcp_rfc1337 == 0) {
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kill:
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inet_twsk_deschedule(tw, &tcp_death_row);
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inet_twsk_put(tw);
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return TCP_TW_SUCCESS;
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}
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}
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inet_twsk_schedule(tw, &tcp_death_row, TCP_TIMEWAIT_LEN,
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TCP_TIMEWAIT_LEN);
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if (tmp_opt.saw_tstamp) {
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tcptw->tw_ts_recent = tmp_opt.rcv_tsval;
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tcptw->tw_ts_recent_stamp = get_seconds();
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}
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inet_twsk_put(tw);
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return TCP_TW_SUCCESS;
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}
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/* Out of window segment.
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All the segments are ACKed immediately.
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The only exception is new SYN. We accept it, if it is
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not old duplicate and we are not in danger to be killed
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by delayed old duplicates. RFC check is that it has
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newer sequence number works at rates <40Mbit/sec.
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However, if paws works, it is reliable AND even more,
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we even may relax silly seq space cutoff.
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RED-PEN: we violate main RFC requirement, if this SYN will appear
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old duplicate (i.e. we receive RST in reply to SYN-ACK),
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we must return socket to time-wait state. It is not good,
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but not fatal yet.
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*/
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if (th->syn && !th->rst && !th->ack && !paws_reject &&
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(after(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt) ||
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(tmp_opt.saw_tstamp &&
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(s32)(tcptw->tw_ts_recent - tmp_opt.rcv_tsval) < 0))) {
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u32 isn = tcptw->tw_snd_nxt + 65535 + 2;
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if (isn == 0)
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isn++;
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TCP_SKB_CB(skb)->when = isn;
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return TCP_TW_SYN;
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}
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if (paws_reject)
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NET_INC_STATS_BH(twsk_net(tw), LINUX_MIB_PAWSESTABREJECTED);
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if (!th->rst) {
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/* In this case we must reset the TIMEWAIT timer.
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*
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* If it is ACKless SYN it may be both old duplicate
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* and new good SYN with random sequence number <rcv_nxt.
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* Do not reschedule in the last case.
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*/
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if (paws_reject || th->ack)
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inet_twsk_schedule(tw, &tcp_death_row, TCP_TIMEWAIT_LEN,
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TCP_TIMEWAIT_LEN);
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/* Send ACK. Note, we do not put the bucket,
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* it will be released by caller.
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*/
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return TCP_TW_ACK;
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}
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inet_twsk_put(tw);
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return TCP_TW_SUCCESS;
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}
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/*
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* Move a socket to time-wait or dead fin-wait-2 state.
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*/
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void tcp_time_wait(struct sock *sk, int state, int timeo)
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{
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struct inet_timewait_sock *tw = NULL;
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const struct inet_connection_sock *icsk = inet_csk(sk);
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const struct tcp_sock *tp = tcp_sk(sk);
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int recycle_ok = 0;
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|
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if (tcp_death_row.sysctl_tw_recycle && tp->rx_opt.ts_recent_stamp)
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recycle_ok = icsk->icsk_af_ops->remember_stamp(sk);
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|
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if (tcp_death_row.tw_count < tcp_death_row.sysctl_max_tw_buckets)
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tw = inet_twsk_alloc(sk, state);
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if (tw != NULL) {
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struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
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const int rto = (icsk->icsk_rto << 2) - (icsk->icsk_rto >> 1);
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tw->tw_rcv_wscale = tp->rx_opt.rcv_wscale;
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tcptw->tw_rcv_nxt = tp->rcv_nxt;
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tcptw->tw_snd_nxt = tp->snd_nxt;
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tcptw->tw_rcv_wnd = tcp_receive_window(tp);
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tcptw->tw_ts_recent = tp->rx_opt.ts_recent;
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tcptw->tw_ts_recent_stamp = tp->rx_opt.ts_recent_stamp;
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|
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#if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
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if (tw->tw_family == PF_INET6) {
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struct ipv6_pinfo *np = inet6_sk(sk);
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struct inet6_timewait_sock *tw6;
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|
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tw->tw_ipv6_offset = inet6_tw_offset(sk->sk_prot);
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tw6 = inet6_twsk((struct sock *)tw);
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ipv6_addr_copy(&tw6->tw_v6_daddr, &np->daddr);
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ipv6_addr_copy(&tw6->tw_v6_rcv_saddr, &np->rcv_saddr);
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tw->tw_ipv6only = np->ipv6only;
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}
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#endif
|
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|
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#ifdef CONFIG_TCP_MD5SIG
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/*
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* The timewait bucket does not have the key DB from the
|
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* sock structure. We just make a quick copy of the
|
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* md5 key being used (if indeed we are using one)
|
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* so the timewait ack generating code has the key.
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*/
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do {
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struct tcp_md5sig_key *key;
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memset(tcptw->tw_md5_key, 0, sizeof(tcptw->tw_md5_key));
|
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tcptw->tw_md5_keylen = 0;
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key = tp->af_specific->md5_lookup(sk, sk);
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if (key != NULL) {
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memcpy(&tcptw->tw_md5_key, key->key, key->keylen);
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tcptw->tw_md5_keylen = key->keylen;
|
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if (tcp_alloc_md5sig_pool() == NULL)
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BUG();
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}
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} while (0);
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#endif
|
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|
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/* Linkage updates. */
|
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__inet_twsk_hashdance(tw, sk, &tcp_hashinfo);
|
|
|
|
/* Get the TIME_WAIT timeout firing. */
|
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if (timeo < rto)
|
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timeo = rto;
|
|
|
|
if (recycle_ok) {
|
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tw->tw_timeout = rto;
|
|
} else {
|
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tw->tw_timeout = TCP_TIMEWAIT_LEN;
|
|
if (state == TCP_TIME_WAIT)
|
|
timeo = TCP_TIMEWAIT_LEN;
|
|
}
|
|
|
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inet_twsk_schedule(tw, &tcp_death_row, timeo,
|
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TCP_TIMEWAIT_LEN);
|
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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.
|
|
*/
|
|
LIMIT_NETDEBUG(KERN_INFO "TCP: time wait bucket table overflow\n");
|
|
}
|
|
|
|
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_keylen)
|
|
tcp_put_md5sig_pool();
|
|
#endif
|
|
}
|
|
|
|
EXPORT_SYMBOL_GPL(tcp_twsk_destructor);
|
|
|
|
static inline void TCP_ECN_openreq_child(struct tcp_sock *tp,
|
|
struct request_sock *req)
|
|
{
|
|
tp->ecn_flags = inet_rsk(req)->ecn_ok ? TCP_ECN_OK : 0;
|
|
}
|
|
|
|
/* 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(sk, req, GFP_ATOMIC);
|
|
|
|
if (newsk != NULL) {
|
|
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;
|
|
|
|
/* Now setup tcp_sock */
|
|
newtp = tcp_sk(newsk);
|
|
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 = treq->snt_isn + 1;
|
|
newtp->snd_up = treq->snt_isn + 1;
|
|
|
|
tcp_prequeue_init(newtp);
|
|
|
|
tcp_init_wl(newtp, treq->rcv_isn);
|
|
|
|
newtp->srtt = 0;
|
|
newtp->mdev = 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 = 0x7fffffff;
|
|
|
|
/* 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 = 2;
|
|
newtp->snd_cwnd_cnt = 0;
|
|
newtp->bytes_acked = 0;
|
|
|
|
newtp->frto_counter = 0;
|
|
newtp->frto_highmark = 0;
|
|
|
|
newicsk->icsk_ca_ops = &tcp_init_congestion_ops;
|
|
|
|
tcp_set_ca_state(newsk, TCP_CA_Open);
|
|
tcp_init_xmit_timers(newsk);
|
|
skb_queue_head_init(&newtp->out_of_order_queue);
|
|
newtp->write_seq = treq->snt_isn + 1;
|
|
newtp->pushed_seq = newtp->write_seq;
|
|
|
|
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);
|
|
}
|
|
#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_MIN_RCVMSS+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);
|
|
|
|
TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_PASSIVEOPENS);
|
|
}
|
|
return newsk;
|
|
}
|
|
|
|
/*
|
|
* Process an incoming packet for SYN_RECV sockets represented
|
|
* as a request_sock.
|
|
*/
|
|
|
|
struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
|
|
struct request_sock *req,
|
|
struct request_sock **prev)
|
|
{
|
|
const struct tcphdr *th = tcp_hdr(skb);
|
|
__be32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK);
|
|
int paws_reject = 0;
|
|
struct tcp_options_received tmp_opt;
|
|
struct sock *child;
|
|
|
|
tmp_opt.saw_tstamp = 0;
|
|
if (th->doff > (sizeof(struct tcphdr)>>2)) {
|
|
tcp_parse_options(skb, &tmp_opt, 0);
|
|
|
|
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->retrans);
|
|
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.
|
|
*/
|
|
req->rsk_ops->rtx_syn_ack(sk, req);
|
|
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
|
|
*/
|
|
if ((flg & TCP_FLAG_ACK) &&
|
|
(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_isn + 1, tcp_rsk(req)->rcv_isn + 1 + 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_isn + 1))
|
|
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.
|
|
*/
|
|
if (!(flg & TCP_FLAG_ACK))
|
|
return NULL;
|
|
|
|
/* If TCP_DEFER_ACCEPT is set, drop bare ACK. */
|
|
if (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;
|
|
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 == NULL)
|
|
goto listen_overflow;
|
|
#ifdef CONFIG_TCP_MD5SIG
|
|
else {
|
|
/* Copy over the MD5 key from the original socket */
|
|
struct tcp_md5sig_key *key;
|
|
struct tcp_sock *tp = tcp_sk(sk);
|
|
key = tp->af_specific->md5_lookup(sk, child);
|
|
if (key != NULL) {
|
|
/*
|
|
* We're using one, so create a matching key on the
|
|
* newsk structure. If we fail to get memory then we
|
|
* end up not copying the key across. Shucks.
|
|
*/
|
|
char *newkey = kmemdup(key->key, key->keylen,
|
|
GFP_ATOMIC);
|
|
if (newkey) {
|
|
if (!tcp_alloc_md5sig_pool())
|
|
BUG();
|
|
tp->af_specific->md5_add(child, child, newkey,
|
|
key->keylen);
|
|
}
|
|
}
|
|
}
|
|
#endif
|
|
|
|
inet_csk_reqsk_queue_unlink(sk, req, prev);
|
|
inet_csk_reqsk_queue_removed(sk, req);
|
|
|
|
inet_csk_reqsk_queue_add(sk, req, child);
|
|
return child;
|
|
|
|
listen_overflow:
|
|
if (!sysctl_tcp_abort_on_overflow) {
|
|
inet_rsk(req)->acked = 1;
|
|
return NULL;
|
|
}
|
|
|
|
embryonic_reset:
|
|
NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_EMBRYONICRSTS);
|
|
if (!(flg & TCP_FLAG_RST))
|
|
req->rsk_ops->send_reset(sk, skb);
|
|
|
|
inet_csk_reqsk_queue_drop(sk, req, prev);
|
|
return NULL;
|
|
}
|
|
|
|
/*
|
|
* Queue segment on the new socket if the new socket is active,
|
|
* otherwise we just shortcircuit this and continue with
|
|
* the new socket.
|
|
*/
|
|
|
|
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, 0);
|
|
} 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_check_req);
|
|
EXPORT_SYMBOL(tcp_child_process);
|
|
EXPORT_SYMBOL(tcp_create_openreq_child);
|
|
EXPORT_SYMBOL(tcp_timewait_state_process);
|
|
|