259 lines
7.1 KiB
C
259 lines
7.1 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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* IPv6 Syncookies implementation for the Linux kernel
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*
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* Authors:
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* Glenn Griffin <ggriffin.kernel@gmail.com>
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*
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* Based on IPv4 implementation by Andi Kleen
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* linux/net/ipv4/syncookies.c
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*/
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#include <linux/tcp.h>
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#include <linux/random.h>
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#include <linux/siphash.h>
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#include <linux/kernel.h>
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#include <net/secure_seq.h>
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#include <net/ipv6.h>
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#include <net/tcp.h>
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#define COOKIEBITS 24 /* Upper bits store count */
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#define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1)
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static siphash_key_t syncookie6_secret[2] __read_mostly;
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/* RFC 2460, Section 8.3:
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* [ipv6 tcp] MSS must be computed as the maximum packet size minus 60 [..]
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*
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* Due to IPV6_MIN_MTU=1280 the lowest possible MSS is 1220, which allows
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* using higher values than ipv4 tcp syncookies.
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* The other values are chosen based on ethernet (1500 and 9k MTU), plus
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* one that accounts for common encap (PPPoe) overhead. Table must be sorted.
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*/
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static __u16 const msstab[] = {
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1280 - 60, /* IPV6_MIN_MTU - 60 */
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1480 - 60,
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1500 - 60,
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9000 - 60,
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};
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static u32 cookie_hash(const struct in6_addr *saddr,
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const struct in6_addr *daddr,
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__be16 sport, __be16 dport, u32 count, int c)
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{
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const struct {
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struct in6_addr saddr;
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struct in6_addr daddr;
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u32 count;
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__be16 sport;
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__be16 dport;
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} __aligned(SIPHASH_ALIGNMENT) combined = {
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.saddr = *saddr,
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.daddr = *daddr,
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.count = count,
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.sport = sport,
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.dport = dport
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};
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net_get_random_once(syncookie6_secret, sizeof(syncookie6_secret));
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return siphash(&combined, offsetofend(typeof(combined), dport),
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&syncookie6_secret[c]);
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}
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static __u32 secure_tcp_syn_cookie(const struct in6_addr *saddr,
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const struct in6_addr *daddr,
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__be16 sport, __be16 dport, __u32 sseq,
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__u32 data)
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{
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u32 count = tcp_cookie_time();
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return (cookie_hash(saddr, daddr, sport, dport, 0, 0) +
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sseq + (count << COOKIEBITS) +
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((cookie_hash(saddr, daddr, sport, dport, count, 1) + data)
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& COOKIEMASK));
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}
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static __u32 check_tcp_syn_cookie(__u32 cookie, const struct in6_addr *saddr,
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const struct in6_addr *daddr, __be16 sport,
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__be16 dport, __u32 sseq)
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{
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__u32 diff, count = tcp_cookie_time();
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cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq;
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diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS);
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if (diff >= MAX_SYNCOOKIE_AGE)
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return (__u32)-1;
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return (cookie -
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cookie_hash(saddr, daddr, sport, dport, count - diff, 1))
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& COOKIEMASK;
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}
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u32 __cookie_v6_init_sequence(const struct ipv6hdr *iph,
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const struct tcphdr *th, __u16 *mssp)
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{
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int mssind;
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const __u16 mss = *mssp;
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for (mssind = ARRAY_SIZE(msstab) - 1; mssind ; mssind--)
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if (mss >= msstab[mssind])
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break;
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*mssp = msstab[mssind];
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return secure_tcp_syn_cookie(&iph->saddr, &iph->daddr, th->source,
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th->dest, ntohl(th->seq), mssind);
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}
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EXPORT_SYMBOL_GPL(__cookie_v6_init_sequence);
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__u32 cookie_v6_init_sequence(const struct sk_buff *skb, __u16 *mssp)
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{
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const struct ipv6hdr *iph = ipv6_hdr(skb);
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const struct tcphdr *th = tcp_hdr(skb);
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return __cookie_v6_init_sequence(iph, th, mssp);
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}
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int __cookie_v6_check(const struct ipv6hdr *iph, const struct tcphdr *th,
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__u32 cookie)
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{
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__u32 seq = ntohl(th->seq) - 1;
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__u32 mssind = check_tcp_syn_cookie(cookie, &iph->saddr, &iph->daddr,
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th->source, th->dest, seq);
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return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0;
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}
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EXPORT_SYMBOL_GPL(__cookie_v6_check);
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struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
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{
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struct tcp_options_received tcp_opt;
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struct inet_request_sock *ireq;
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struct tcp_request_sock *treq;
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struct ipv6_pinfo *np = inet6_sk(sk);
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struct tcp_sock *tp = tcp_sk(sk);
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const struct tcphdr *th = tcp_hdr(skb);
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__u32 cookie = ntohl(th->ack_seq) - 1;
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struct sock *ret = sk;
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struct request_sock *req;
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int mss;
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struct dst_entry *dst;
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__u8 rcv_wscale;
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u32 tsoff = 0;
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if (!sock_net(sk)->ipv4.sysctl_tcp_syncookies || !th->ack || th->rst)
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goto out;
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if (tcp_synq_no_recent_overflow(sk))
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goto out;
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mss = __cookie_v6_check(ipv6_hdr(skb), th, cookie);
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if (mss == 0) {
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__NET_INC_STATS(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED);
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goto out;
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}
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__NET_INC_STATS(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV);
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/* check for timestamp cookie support */
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memset(&tcp_opt, 0, sizeof(tcp_opt));
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tcp_parse_options(sock_net(sk), skb, &tcp_opt, 0, NULL);
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if (tcp_opt.saw_tstamp && tcp_opt.rcv_tsecr) {
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tsoff = secure_tcpv6_ts_off(sock_net(sk),
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ipv6_hdr(skb)->daddr.s6_addr32,
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ipv6_hdr(skb)->saddr.s6_addr32);
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tcp_opt.rcv_tsecr -= tsoff;
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}
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if (!cookie_timestamp_decode(sock_net(sk), &tcp_opt))
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goto out;
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ret = NULL;
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req = inet_reqsk_alloc(&tcp6_request_sock_ops, sk, false);
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if (!req)
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goto out;
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ireq = inet_rsk(req);
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treq = tcp_rsk(req);
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treq->tfo_listener = false;
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if (security_inet_conn_request(sk, skb, req))
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goto out_free;
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req->mss = mss;
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ireq->ir_rmt_port = th->source;
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ireq->ir_num = ntohs(th->dest);
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ireq->ir_v6_rmt_addr = ipv6_hdr(skb)->saddr;
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ireq->ir_v6_loc_addr = ipv6_hdr(skb)->daddr;
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if (ipv6_opt_accepted(sk, skb, &TCP_SKB_CB(skb)->header.h6) ||
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np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo ||
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np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) {
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refcount_inc(&skb->users);
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ireq->pktopts = skb;
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}
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ireq->ir_iif = inet_request_bound_dev_if(sk, skb);
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/* So that link locals have meaning */
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if (!sk->sk_bound_dev_if &&
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ipv6_addr_type(&ireq->ir_v6_rmt_addr) & IPV6_ADDR_LINKLOCAL)
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ireq->ir_iif = tcp_v6_iif(skb);
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ireq->ir_mark = inet_request_mark(sk, skb);
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req->num_retrans = 0;
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ireq->snd_wscale = tcp_opt.snd_wscale;
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ireq->sack_ok = tcp_opt.sack_ok;
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ireq->wscale_ok = tcp_opt.wscale_ok;
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ireq->tstamp_ok = tcp_opt.saw_tstamp;
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req->ts_recent = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0;
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treq->snt_synack = 0;
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treq->rcv_isn = ntohl(th->seq) - 1;
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treq->snt_isn = cookie;
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treq->ts_off = 0;
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treq->txhash = net_tx_rndhash();
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if (IS_ENABLED(CONFIG_SMC))
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ireq->smc_ok = 0;
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/*
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* We need to lookup the dst_entry to get the correct window size.
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* This is taken from tcp_v6_syn_recv_sock. Somebody please enlighten
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* me if there is a preferred way.
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*/
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{
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struct in6_addr *final_p, final;
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struct flowi6 fl6;
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memset(&fl6, 0, sizeof(fl6));
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fl6.flowi6_proto = IPPROTO_TCP;
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fl6.daddr = ireq->ir_v6_rmt_addr;
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final_p = fl6_update_dst(&fl6, rcu_dereference(np->opt), &final);
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fl6.saddr = ireq->ir_v6_loc_addr;
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fl6.flowi6_oif = ireq->ir_iif;
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fl6.flowi6_mark = ireq->ir_mark;
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fl6.fl6_dport = ireq->ir_rmt_port;
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fl6.fl6_sport = inet_sk(sk)->inet_sport;
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fl6.flowi6_uid = sk->sk_uid;
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security_req_classify_flow(req, flowi6_to_flowi(&fl6));
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dst = ip6_dst_lookup_flow(sk, &fl6, final_p);
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if (IS_ERR(dst))
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goto out_free;
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}
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req->rsk_window_clamp = tp->window_clamp ? :dst_metric(dst, RTAX_WINDOW);
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tcp_select_initial_window(sk, tcp_full_space(sk), req->mss,
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&req->rsk_rcv_wnd, &req->rsk_window_clamp,
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ireq->wscale_ok, &rcv_wscale,
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dst_metric(dst, RTAX_INITRWND));
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ireq->rcv_wscale = rcv_wscale;
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ireq->ecn_ok = cookie_ecn_ok(&tcp_opt, sock_net(sk), dst);
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ret = tcp_get_cookie_sock(sk, skb, req, dst, tsoff);
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out:
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return ret;
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out_free:
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reqsk_free(req);
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return NULL;
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}
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