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860 lines
27 KiB
860 lines
27 KiB
// SPDX-License-Identifier: GPL-2.0-only |
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/* |
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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, <[email protected]> |
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* Mark Evans, <[email protected]> |
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* Corey Minyard <[email protected]> |
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* Florian La Roche, <[email protected]> |
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* Charles Hedrick, <[email protected]> |
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* Linus Torvalds, <[email protected]> |
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* Alan Cox, <[email protected]> |
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* Matthew Dillon, <[email protected]> |
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* Arnt Gulbrandsen, <[email protected]> |
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* Jorge Cwik, <[email protected]> |
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*/ |
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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/slab.h> |
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#include <linux/sysctl.h> |
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#include <linux/workqueue.h> |
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#include <linux/static_key.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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#include <net/busy_poll.h> |
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|
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static bool 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 true; |
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if (after(end_seq, s_win) && before(seq, e_win)) |
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return true; |
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return seq == e_win && seq == end_seq; |
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} |
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static enum tcp_tw_status |
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tcp_timewait_check_oow_rate_limit(struct inet_timewait_sock *tw, |
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const struct sk_buff *skb, int mib_idx) |
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{ |
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struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); |
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|
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if (!tcp_oow_rate_limited(twsk_net(tw), skb, mib_idx, |
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&tcptw->tw_last_oow_ack_time)) { |
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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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|
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/* We are rate-limiting, so just release the tw sock and drop skb. */ |
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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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/* |
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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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* We don't need to initialize tmp_out.sack_ok as we don't use the results |
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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_options_received tmp_opt; |
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struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); |
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bool paws_reject = false; |
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|
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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(twsk_net(tw), skb, &tmp_opt, 0, NULL); |
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|
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if (tmp_opt.saw_tstamp) { |
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if (tmp_opt.rcv_tsecr) |
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tmp_opt.rcv_tsecr -= tcptw->tw_ts_offset; |
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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_timewait_check_oow_rate_limit( |
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tw, skb, LINUX_MIB_TCPACKSKIPPEDFINWAIT2); |
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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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return TCP_TW_RST; |
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|
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/* Dup ACK? */ |
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if (!th->ack || |
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!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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return TCP_TW_RST; |
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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 = ktime_get_seconds(); |
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tcptw->tw_ts_recent = tmp_opt.rcv_tsval; |
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} |
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inet_twsk_reschedule(tw, 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 (twsk_net(tw)->ipv4.sysctl_tcp_rfc1337 == 0) { |
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kill: |
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inet_twsk_deschedule_put(tw); |
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return TCP_TW_SUCCESS; |
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} |
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} else { |
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inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN); |
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} |
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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 = ktime_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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|
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All the segments are ACKed immediately. |
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|
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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)->tcp_tw_isn = 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(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_reschedule(tw, TCP_TIMEWAIT_LEN); |
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return tcp_timewait_check_oow_rate_limit( |
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tw, skb, LINUX_MIB_TCPACKSKIPPEDTIMEWAIT); |
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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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EXPORT_SYMBOL(tcp_timewait_state_process); |
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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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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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struct inet_timewait_sock *tw; |
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struct inet_timewait_death_row *tcp_death_row = &sock_net(sk)->ipv4.tcp_death_row; |
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tw = inet_twsk_alloc(sk, tcp_death_row, state); |
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if (tw) { |
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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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struct inet_sock *inet = inet_sk(sk); |
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tw->tw_transparent = inet->transparent; |
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tw->tw_mark = sk->sk_mark; |
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tw->tw_priority = sk->sk_priority; |
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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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tcptw->tw_ts_offset = tp->tsoffset; |
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tcptw->tw_last_oow_ack_time = 0; |
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tcptw->tw_tx_delay = tp->tcp_tx_delay; |
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#if IS_ENABLED(CONFIG_IPV6) |
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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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tw->tw_v6_daddr = sk->sk_v6_daddr; |
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tw->tw_v6_rcv_saddr = sk->sk_v6_rcv_saddr; |
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tw->tw_tclass = np->tclass; |
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tw->tw_flowlabel = be32_to_cpu(np->flow_label & IPV6_FLOWLABEL_MASK); |
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tw->tw_txhash = sk->sk_txhash; |
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tw->tw_ipv6only = sk->sk_ipv6only; |
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} |
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#endif |
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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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tcptw->tw_md5_key = NULL; |
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if (static_branch_unlikely(&tcp_md5_needed)) { |
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struct tcp_md5sig_key *key; |
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key = tp->af_specific->md5_lookup(sk, sk); |
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if (key) { |
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tcptw->tw_md5_key = kmemdup(key, sizeof(*key), GFP_ATOMIC); |
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BUG_ON(tcptw->tw_md5_key && !tcp_alloc_md5sig_pool()); |
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} |
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} |
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} while (0); |
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#endif |
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/* Get the TIME_WAIT timeout firing. */ |
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if (timeo < rto) |
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timeo = rto; |
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if (state == TCP_TIME_WAIT) |
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timeo = TCP_TIMEWAIT_LEN; |
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|
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/* tw_timer is pinned, so we need to make sure BH are disabled |
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* in following section, otherwise timer handler could run before |
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* we complete the initialization. |
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*/ |
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local_bh_disable(); |
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inet_twsk_schedule(tw, timeo); |
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/* Linkage updates. |
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* Note that access to tw after this point is illegal. |
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*/ |
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inet_twsk_hashdance(tw, sk, &tcp_hashinfo); |
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local_bh_enable(); |
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} else { |
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/* Sorry, if we're out of memory, just CLOSE this |
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* socket up. We've got bigger problems than |
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* non-graceful socket closings. |
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*/ |
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NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPTIMEWAITOVERFLOW); |
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} |
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tcp_update_metrics(sk); |
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tcp_done(sk); |
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} |
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EXPORT_SYMBOL(tcp_time_wait); |
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|
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void tcp_twsk_destructor(struct sock *sk) |
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{ |
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#ifdef CONFIG_TCP_MD5SIG |
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if (static_branch_unlikely(&tcp_md5_needed)) { |
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struct tcp_timewait_sock *twsk = tcp_twsk(sk); |
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if (twsk->tw_md5_key) |
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kfree_rcu(twsk->tw_md5_key, rcu); |
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} |
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#endif |
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} |
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EXPORT_SYMBOL_GPL(tcp_twsk_destructor); |
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|
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/* Warning : This function is called without sk_listener being locked. |
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* Be sure to read socket fields once, as their value could change under us. |
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*/ |
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void tcp_openreq_init_rwin(struct request_sock *req, |
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const struct sock *sk_listener, |
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const struct dst_entry *dst) |
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{ |
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struct inet_request_sock *ireq = inet_rsk(req); |
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const struct tcp_sock *tp = tcp_sk(sk_listener); |
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int full_space = tcp_full_space(sk_listener); |
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u32 window_clamp; |
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__u8 rcv_wscale; |
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u32 rcv_wnd; |
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int mss; |
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mss = tcp_mss_clamp(tp, dst_metric_advmss(dst)); |
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window_clamp = READ_ONCE(tp->window_clamp); |
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/* Set this up on the first call only */ |
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req->rsk_window_clamp = window_clamp ? : dst_metric(dst, RTAX_WINDOW); |
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|
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/* limit the window selection if the user enforce a smaller rx buffer */ |
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if (sk_listener->sk_userlocks & SOCK_RCVBUF_LOCK && |
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(req->rsk_window_clamp > full_space || req->rsk_window_clamp == 0)) |
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req->rsk_window_clamp = full_space; |
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rcv_wnd = tcp_rwnd_init_bpf((struct sock *)req); |
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if (rcv_wnd == 0) |
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rcv_wnd = dst_metric(dst, RTAX_INITRWND); |
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else if (full_space < rcv_wnd * mss) |
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full_space = rcv_wnd * mss; |
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|
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/* tcp_full_space because it is guaranteed to be the first packet */ |
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tcp_select_initial_window(sk_listener, full_space, |
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mss - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0), |
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&req->rsk_rcv_wnd, |
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&req->rsk_window_clamp, |
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ireq->wscale_ok, |
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&rcv_wscale, |
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rcv_wnd); |
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ireq->rcv_wscale = rcv_wscale; |
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} |
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EXPORT_SYMBOL(tcp_openreq_init_rwin); |
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|
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static void tcp_ecn_openreq_child(struct tcp_sock *tp, |
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const struct request_sock *req) |
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{ |
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tp->ecn_flags = inet_rsk(req)->ecn_ok ? TCP_ECN_OK : 0; |
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} |
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|
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void tcp_ca_openreq_child(struct sock *sk, const struct dst_entry *dst) |
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{ |
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struct inet_connection_sock *icsk = inet_csk(sk); |
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u32 ca_key = dst_metric(dst, RTAX_CC_ALGO); |
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bool ca_got_dst = false; |
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|
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if (ca_key != TCP_CA_UNSPEC) { |
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const struct tcp_congestion_ops *ca; |
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|
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rcu_read_lock(); |
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ca = tcp_ca_find_key(ca_key); |
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if (likely(ca && bpf_try_module_get(ca, ca->owner))) { |
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icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst); |
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icsk->icsk_ca_ops = ca; |
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ca_got_dst = true; |
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} |
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rcu_read_unlock(); |
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} |
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|
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/* If no valid choice made yet, assign current system default ca. */ |
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if (!ca_got_dst && |
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(!icsk->icsk_ca_setsockopt || |
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!bpf_try_module_get(icsk->icsk_ca_ops, icsk->icsk_ca_ops->owner))) |
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tcp_assign_congestion_control(sk); |
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|
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tcp_set_ca_state(sk, TCP_CA_Open); |
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} |
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EXPORT_SYMBOL_GPL(tcp_ca_openreq_child); |
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|
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static void smc_check_reset_syn_req(struct tcp_sock *oldtp, |
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struct request_sock *req, |
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struct tcp_sock *newtp) |
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{ |
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#if IS_ENABLED(CONFIG_SMC) |
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struct inet_request_sock *ireq; |
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|
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if (static_branch_unlikely(&tcp_have_smc)) { |
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ireq = inet_rsk(req); |
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if (oldtp->syn_smc && !ireq->smc_ok) |
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newtp->syn_smc = 0; |
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} |
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#endif |
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} |
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|
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/* This is not only more efficient than what we used to do, it eliminates |
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* a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM |
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* |
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* Actually, we could lots of memory writes here. tp of listening |
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* socket contains all necessary default parameters. |
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*/ |
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struct sock *tcp_create_openreq_child(const struct sock *sk, |
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struct request_sock *req, |
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struct sk_buff *skb) |
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{ |
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struct sock *newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC); |
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const struct inet_request_sock *ireq = inet_rsk(req); |
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struct tcp_request_sock *treq = tcp_rsk(req); |
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struct inet_connection_sock *newicsk; |
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struct tcp_sock *oldtp, *newtp; |
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u32 seq; |
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|
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if (!newsk) |
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return NULL; |
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newicsk = inet_csk(newsk); |
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newtp = tcp_sk(newsk); |
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oldtp = tcp_sk(sk); |
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|
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smc_check_reset_syn_req(oldtp, req, newtp); |
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|
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/* Now setup tcp_sock */ |
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newtp->pred_flags = 0; |
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|
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seq = treq->rcv_isn + 1; |
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newtp->rcv_wup = seq; |
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WRITE_ONCE(newtp->copied_seq, seq); |
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WRITE_ONCE(newtp->rcv_nxt, seq); |
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newtp->segs_in = 1; |
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|
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seq = treq->snt_isn + 1; |
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newtp->snd_sml = newtp->snd_una = seq; |
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WRITE_ONCE(newtp->snd_nxt, seq); |
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newtp->snd_up = seq; |
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|
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INIT_LIST_HEAD(&newtp->tsq_node); |
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INIT_LIST_HEAD(&newtp->tsorted_sent_queue); |
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|
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tcp_init_wl(newtp, treq->rcv_isn); |
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|
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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); |
|
WRITE_ONCE(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; |
|
RCU_INIT_POINTER(newtp->fastopen_rsk, NULL); |
|
|
|
tcp_bpf_clone(sk, newsk); |
|
|
|
__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; |
|
|
|
if (own_req && rsk_drop_req(req)) { |
|
reqsk_queue_removed(&inet_csk(req->rsk_listener)->icsk_accept_queue, req); |
|
inet_csk_reqsk_queue_drop_and_put(req->rsk_listener, req); |
|
return child; |
|
} |
|
|
|
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 (sk != req->rsk_listener) |
|
__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMIGRATEREQFAILURE); |
|
|
|
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, skb); |
|
} |
|
if (!fastopen) { |
|
bool unlinked = inet_csk_reqsk_queue_drop(sk, req); |
|
|
|
if (unlinked) |
|
__NET_INC_STATS(sock_net(sk), LINUX_MIB_EMBRYONICRSTS); |
|
*req_stolen = !unlinked; |
|
} |
|
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) |
|
__releases(&((child)->sk_lock.slock)) |
|
{ |
|
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);
|
|
|