268 lines
7.2 KiB
C
268 lines
7.2 KiB
C
/*
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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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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version
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* 2 of the License, or (at your option) any later version.
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*
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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/cryptohash.h>
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#include <linux/kernel.h>
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#include <net/ipv6.h>
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#include <net/tcp.h>
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extern int sysctl_tcp_syncookies;
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extern __u32 syncookie_secret[2][16-4+SHA_DIGEST_WORDS];
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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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/* Table must be sorted. */
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static __u16 const msstab[] = {
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64,
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512,
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536,
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1280 - 60,
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1480 - 60,
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1500 - 60,
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4460 - 60,
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9000 - 60,
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};
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/*
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* This (misnamed) value is the age of syncookie which is permitted.
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* Its ideal value should be dependent on TCP_TIMEOUT_INIT and
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* sysctl_tcp_retries1. It's a rather complicated formula (exponential
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* backoff) to compute at runtime so it's currently hardcoded here.
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*/
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#define COUNTER_TRIES 4
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static inline struct sock *get_cookie_sock(struct sock *sk, struct sk_buff *skb,
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struct request_sock *req,
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struct dst_entry *dst)
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{
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struct inet_connection_sock *icsk = inet_csk(sk);
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struct sock *child;
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child = icsk->icsk_af_ops->syn_recv_sock(sk, skb, req, dst);
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if (child)
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inet_csk_reqsk_queue_add(sk, req, child);
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else
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reqsk_free(req);
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return child;
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}
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static DEFINE_PER_CPU(__u32 [16 + 5 + SHA_WORKSPACE_WORDS],
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ipv6_cookie_scratch);
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static u32 cookie_hash(struct in6_addr *saddr, struct in6_addr *daddr,
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__be16 sport, __be16 dport, u32 count, int c)
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{
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__u32 *tmp = __get_cpu_var(ipv6_cookie_scratch);
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/*
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* we have 320 bits of information to hash, copy in the remaining
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* 192 bits required for sha_transform, from the syncookie_secret
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* and overwrite the digest with the secret
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*/
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memcpy(tmp + 10, syncookie_secret[c], 44);
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memcpy(tmp, saddr, 16);
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memcpy(tmp + 4, daddr, 16);
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tmp[8] = ((__force u32)sport << 16) + (__force u32)dport;
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tmp[9] = count;
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sha_transform(tmp + 16, (__u8 *)tmp, tmp + 16 + 5);
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return tmp[17];
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}
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static __u32 secure_tcp_syn_cookie(struct in6_addr *saddr, struct in6_addr *daddr,
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__be16 sport, __be16 dport, __u32 sseq,
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__u32 count, __u32 data)
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{
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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, struct in6_addr *saddr,
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struct in6_addr *daddr, __be16 sport,
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__be16 dport, __u32 sseq, __u32 count,
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__u32 maxdiff)
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{
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__u32 diff;
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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 >= maxdiff)
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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(struct sock *sk, struct sk_buff *skb, __u16 *mssp)
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{
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struct ipv6hdr *iph = ipv6_hdr(skb);
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const struct tcphdr *th = tcp_hdr(skb);
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int mssind;
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const __u16 mss = *mssp;
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tcp_synq_overflow(sk);
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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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NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESSENT);
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return secure_tcp_syn_cookie(&iph->saddr, &iph->daddr, th->source,
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th->dest, ntohl(th->seq),
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jiffies / (HZ * 60), mssind);
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}
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static inline int cookie_check(struct sk_buff *skb, __u32 cookie)
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{
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struct ipv6hdr *iph = ipv6_hdr(skb);
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const struct tcphdr *th = tcp_hdr(skb);
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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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jiffies / (HZ * 60), COUNTER_TRIES);
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return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0;
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}
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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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u8 *hash_location;
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struct inet_request_sock *ireq;
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struct inet6_request_sock *ireq6;
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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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bool ecn_ok;
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if (!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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(mss = cookie_check(skb, cookie)) == 0) {
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NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED);
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goto out;
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}
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NET_INC_STATS_BH(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(skb, &tcp_opt, &hash_location, 0);
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if (!cookie_check_timestamp(&tcp_opt, &ecn_ok))
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goto out;
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ret = NULL;
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req = inet6_reqsk_alloc(&tcp6_request_sock_ops);
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if (!req)
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goto out;
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ireq = inet_rsk(req);
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ireq6 = inet6_rsk(req);
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treq = tcp_rsk(req);
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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->rmt_port = th->source;
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ireq->loc_port = th->dest;
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ipv6_addr_copy(&ireq6->rmt_addr, &ipv6_hdr(skb)->saddr);
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ipv6_addr_copy(&ireq6->loc_addr, &ipv6_hdr(skb)->daddr);
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if (ipv6_opt_accepted(sk, skb) ||
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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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atomic_inc(&skb->users);
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ireq6->pktopts = skb;
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}
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ireq6->iif = sk->sk_bound_dev_if;
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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(&ireq6->rmt_addr) & IPV6_ADDR_LINKLOCAL)
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ireq6->iif = inet6_iif(skb);
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req->expires = 0UL;
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req->retrans = 0;
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ireq->ecn_ok = ecn_ok;
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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->rcv_isn = ntohl(th->seq) - 1;
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treq->snt_isn = cookie;
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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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ipv6_addr_copy(&fl6.daddr, &ireq6->rmt_addr);
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final_p = fl6_update_dst(&fl6, np->opt, &final);
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ipv6_addr_copy(&fl6.saddr, &ireq6->loc_addr);
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fl6.flowi6_oif = sk->sk_bound_dev_if;
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fl6.flowi6_mark = sk->sk_mark;
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fl6.fl6_dport = inet_rsk(req)->rmt_port;
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fl6.fl6_sport = inet_sk(sk)->inet_sport;
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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, false);
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if (IS_ERR(dst))
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goto out_free;
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}
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req->window_clamp = tp->window_clamp ? :dst_metric(dst, RTAX_WINDOW);
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tcp_select_initial_window(tcp_full_space(sk), req->mss,
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&req->rcv_wnd, &req->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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ret = get_cookie_sock(sk, skb, req, dst);
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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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