Release 4.14 net/ipv6/syncookies.c

/*
 *  IPv6 Syncookies implementation for the Linux kernel
 *
 *  Authors:
 *  Glenn Griffin       <ggriffin.kernel@gmail.com>
 *
 *  Based on IPv4 implementation by Andi Kleen
 *  linux/net/ipv4/syncookies.c
 *
 *      This program is free software; you can redistribute it and/or
 *      modify it under the terms of the GNU General Public License
 *      as published by the Free Software Foundation; either version
 *      2 of the License, or (at your option) any later version.
 *
 */

#include <linux/tcp.h>
#include <linux/random.h>
#include <linux/siphash.h>
#include <linux/kernel.h>
#include <net/secure_seq.h>
#include <net/ipv6.h>
#include <net/tcp.h>


#define COOKIEBITS 24	
/* Upper bits store count */

#define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1)


static siphash_key_t syncookie6_secret[2] __read_mostly;

/* RFC 2460, Section 8.3:
 * [ipv6 tcp] MSS must be computed as the maximum packet size minus 60 [..]
 *
 * Due to IPV6_MIN_MTU=1280 the lowest possible MSS is 1220, which allows
 * using higher values than ipv4 tcp syncookies.
 * The other values are chosen based on ethernet (1500 and 9k MTU), plus
 * one that accounts for common encap (PPPoe) overhead. Table must be sorted.
 */

static __u16 const msstab[] = {
	1280 - 60, /* IPV6_MIN_MTU - 60 */
	1480 - 60,
	1500 - 60,
	9000 - 60,
};



static u32 cookie_hash(const struct in6_addr *saddr,
		       const struct in6_addr *daddr,
		       __be16 sport, __be16 dport, u32 count, int c)
{
	const struct {
		struct in6_addr saddr;
		struct in6_addr daddr;
		u32 count;
		__be16 sport;
		__be16 dport;
	} __aligned(SIPHASH_ALIGNMENT) combined = {
		.saddr = *saddr,
		.daddr = *daddr,
		.count = count,
		.sport = sport,
		.dport = dport
	};

	net_get_random_once(syncookie6_secret, sizeof(syncookie6_secret));
	return siphash(&combined, offsetofend(typeof(combined), dport),
		       &syncookie6_secret[c]);
}

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CommitProp
Jason A. Donenfeld
68
57.14%
1
25.00%
Glenn Griffin
38
31.93%
1
25.00%
Hannes Frederic Sowa
11
9.24%
1
25.00%
Eric Dumazet
2
1.68%
1
25.00%
Total
119
100.00%
4
100.00%



static __u32 secure_tcp_syn_cookie(const struct in6_addr *saddr,
				   const struct in6_addr *daddr,
				   __be16 sport, __be16 dport, __u32 sseq,
				   __u32 data)
{
	u32 count = tcp_cookie_time();
	return (cookie_hash(saddr, daddr, sport, dport, 0, 0) +
		sseq + (count << COOKIEBITS) +
		((cookie_hash(saddr, daddr, sport, dport, count, 1) + data)
		& COOKIEMASK));
}

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Glenn Griffin
77
90.59%
1
33.33%
Florian Westphal
6
7.06%
1
33.33%
Eric Dumazet
2
2.35%
1
33.33%
Total
85
100.00%
3
100.00%



static __u32 check_tcp_syn_cookie(__u32 cookie, const struct in6_addr *saddr,
				  const struct in6_addr *daddr, __be16 sport,
				  __be16 dport, __u32 sseq)
{
	__u32 diff, count = tcp_cookie_time();

	cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq;

	diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS);
	if (diff >= MAX_SYNCOOKIE_AGE)
		return (__u32)-1;

	return (cookie -
		cookie_hash(saddr, daddr, sport, dport, count - diff, 1))
		& COOKIEMASK;
}

Contributors
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Glenn Griffin
108
93.10%
1
33.33%
Florian Westphal
6
5.17%
1
33.33%
Eric Dumazet
2
1.72%
1
33.33%
Total
116
100.00%
3
100.00%



u32 __cookie_v6_init_sequence(const struct ipv6hdr *iph,
			      const struct tcphdr *th, __u16 *mssp)
{
	int mssind;
	const __u16 mss = *mssp;

	for (mssind = ARRAY_SIZE(msstab) - 1; mssind ; mssind--)
		if (mss >= msstab[mssind])
			break;

	*mssp = msstab[mssind];

	return secure_tcp_syn_cookie(&iph->saddr, &iph->daddr, th->source,
				     th->dest, ntohl(th->seq), mssind);
}
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Glenn Griffin
72
75.00%
1
25.00%
Florian Westphal
16
16.67%
1
25.00%
Patrick McHardy
7
7.29%
1
25.00%
Eric Dumazet
1
1.04%
1
25.00%
Total
96
100.00%
4
100.00%


EXPORT_SYMBOL_GPL(__cookie_v6_init_sequence);



__u32 cookie_v6_init_sequence(const struct sk_buff *skb, __u16 *mssp)
{
	const struct ipv6hdr *iph = ipv6_hdr(skb);
	const struct tcphdr *th = tcp_hdr(skb);

	return __cookie_v6_init_sequence(iph, th, mssp);
}

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Glenn Griffin
29
61.70%
1
25.00%
Patrick McHardy
16
34.04%
1
25.00%
Eric Dumazet
2
4.26%
2
50.00%
Total
47
100.00%
4
100.00%



int __cookie_v6_check(const struct ipv6hdr *iph, const struct tcphdr *th,
		      __u32 cookie)
{
	__u32 seq = ntohl(th->seq) - 1;
	__u32 mssind = check_tcp_syn_cookie(cookie, &iph->saddr, &iph->daddr,
					    th->source, th->dest, seq);

	return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0;
}
Contributors
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Glenn Griffin
52
69.33%
1
33.33%
Patrick McHardy
19
25.33%
1
33.33%
Florian Westphal
4
5.33%
1
33.33%
Total
75
100.00%
3
100.00%


EXPORT_SYMBOL_GPL(__cookie_v6_check);



struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
{
	struct tcp_options_received tcp_opt;
	struct inet_request_sock *ireq;
	struct tcp_request_sock *treq;
	struct ipv6_pinfo *np = inet6_sk(sk);
	struct tcp_sock *tp = tcp_sk(sk);
	const struct tcphdr *th = tcp_hdr(skb);
	__u32 cookie = ntohl(th->ack_seq) - 1;
	struct sock *ret = sk;
	struct request_sock *req;
	int mss;
	struct dst_entry *dst;
	__u8 rcv_wscale;
	u32 tsoff = 0;

	if (!sock_net(sk)->ipv4.sysctl_tcp_syncookies || !th->ack || th->rst)
		goto out;

	if (tcp_synq_no_recent_overflow(sk))
		goto out;

	mss = __cookie_v6_check(ipv6_hdr(skb), th, cookie);
	if (mss == 0) {
		__NET_INC_STATS(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED);
		goto out;
	}

	__NET_INC_STATS(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV);

	/* check for timestamp cookie support */
	memset(&tcp_opt, 0, sizeof(tcp_opt));
	tcp_parse_options(sock_net(sk), skb, &tcp_opt, 0, NULL);

	if (tcp_opt.saw_tstamp && tcp_opt.rcv_tsecr) {
		tsoff = secure_tcpv6_ts_off(sock_net(sk),
					    ipv6_hdr(skb)->daddr.s6_addr32,
					    ipv6_hdr(skb)->saddr.s6_addr32);
		tcp_opt.rcv_tsecr -= tsoff;
	}

	if (!cookie_timestamp_decode(sock_net(sk), &tcp_opt))
		goto out;

	ret = NULL;
	req = inet_reqsk_alloc(&tcp6_request_sock_ops, sk, false);
	if (!req)
		goto out;

	ireq = inet_rsk(req);
	treq = tcp_rsk(req);
	treq->tfo_listener = false;

	if (security_inet_conn_request(sk, skb, req))
		goto out_free;

	req->mss = mss;
	ireq->ir_rmt_port = th->source;
	ireq->ir_num = ntohs(th->dest);
	ireq->ir_v6_rmt_addr = ipv6_hdr(skb)->saddr;
	ireq->ir_v6_loc_addr = ipv6_hdr(skb)->daddr;
	if (ipv6_opt_accepted(sk, skb, &TCP_SKB_CB(skb)->header.h6) ||
	    np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo ||
	    np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) {
		refcount_inc(&skb->users);
		ireq->pktopts = skb;
	}

	ireq->ir_iif = inet_request_bound_dev_if(sk, skb);
	/* So that link locals have meaning */
	if (!sk->sk_bound_dev_if &&
	    ipv6_addr_type(&ireq->ir_v6_rmt_addr) & IPV6_ADDR_LINKLOCAL)
		ireq->ir_iif = tcp_v6_iif(skb);

	ireq->ir_mark = inet_request_mark(sk, skb);

	req->num_retrans = 0;
	ireq->snd_wscale	= tcp_opt.snd_wscale;
	ireq->sack_ok		= tcp_opt.sack_ok;
	ireq->wscale_ok		= tcp_opt.wscale_ok;
	ireq->tstamp_ok		= tcp_opt.saw_tstamp;
	req->ts_recent		= tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0;
	treq->snt_synack	= 0;
	treq->rcv_isn = ntohl(th->seq) - 1;
	treq->snt_isn = cookie;
	treq->ts_off = 0;
	treq->txhash = net_tx_rndhash();

	/*
         * We need to lookup the dst_entry to get the correct window size.
         * This is taken from tcp_v6_syn_recv_sock.  Somebody please enlighten
         * me if there is a preferred way.
         */
	{
		struct in6_addr *final_p, final;
		struct flowi6 fl6;
		memset(&fl6, 0, sizeof(fl6));
		fl6.flowi6_proto = IPPROTO_TCP;
		fl6.daddr = ireq->ir_v6_rmt_addr;
		final_p = fl6_update_dst(&fl6, rcu_dereference(np->opt), &final);
		fl6.saddr = ireq->ir_v6_loc_addr;
		fl6.flowi6_oif = ireq->ir_iif;
		fl6.flowi6_mark = ireq->ir_mark;
		fl6.fl6_dport = ireq->ir_rmt_port;
		fl6.fl6_sport = inet_sk(sk)->inet_sport;
		fl6.flowi6_uid = sk->sk_uid;
		security_req_classify_flow(req, flowi6_to_flowi(&fl6));

		dst = ip6_dst_lookup_flow(sk, &fl6, final_p);
		if (IS_ERR(dst))
			goto out_free;
	}

	req->rsk_window_clamp = tp->window_clamp ? :dst_metric(dst, RTAX_WINDOW);
	tcp_select_initial_window(tcp_full_space(sk), req->mss,
				  &req->rsk_rcv_wnd, &req->rsk_window_clamp,
				  ireq->wscale_ok, &rcv_wscale,
				  dst_metric(dst, RTAX_INITRWND));

	ireq->rcv_wscale = rcv_wscale;
	ireq->ecn_ok = cookie_ecn_ok(&tcp_opt, sock_net(sk), dst);

	ret = tcp_get_cookie_sock(sk, skb, req, dst, tsoff);
out:
	return ret;
out_free:
	reqsk_free(req);
	return NULL;
}
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Glenn Griffin
450
53.96%
1
1.96%
Eric Dumazet
113
13.55%
17
33.33%
David S. Miller
103
12.35%
4
7.84%
Florian Westphal
63
7.55%
9
17.65%
Lorenzo Colitti
21
2.52%
2
3.92%
Pavel Emelyanov
10
1.20%
1
1.96%
Jerry Chu
9
1.08%
2
3.92%
Arnaud Ebalard
7
0.84%
1
1.96%
Laurent Chavey
7
0.84%
1
1.96%
Alexander Potapenko
7
0.84%
1
1.96%
David Ahern
7
0.84%
1
1.96%
KOVACS Krisztian
7
0.84%
1
1.96%
Nikolay Borisov
7
0.84%
1
1.96%
Patrick McHardy
6
0.72%
1
1.96%
Alexey Dobriyan
5
0.60%
2
3.92%
William Allen Simpson
4
0.48%
1
1.96%
Yuchung Cheng
3
0.36%
2
3.92%
Brian Haley
3
0.36%
1
1.96%
Octavian Purdila
1
0.12%
1
1.96%
Elena Reshetova
1
0.12%
1
1.96%
Total
834
100.00%
51
100.00%

Overall Contributors
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Glenn Griffin
868
59.99%
1
1.69%
Eric Dumazet
125
8.64%
19
32.20%
Florian Westphal
107
7.39%
13
22.03%
David S. Miller
103
7.12%
4
6.78%
Jason A. Donenfeld
70
4.84%
1
1.69%
Patrick McHardy
58
4.01%
1
1.69%
Lorenzo Colitti
21
1.45%
2
3.39%
Hannes Frederic Sowa
17
1.17%
1
1.69%
Pavel Emelyanov
10
0.69%
1
1.69%
Jerry Chu
9
0.62%
2
3.39%
Arnaud Ebalard
7
0.48%
1
1.69%
Laurent Chavey
7
0.48%
1
1.69%
Alexander Potapenko
7
0.48%
1
1.69%
Nikolay Borisov
7
0.48%
1
1.69%
KOVACS Krisztian
7
0.48%
1
1.69%
David Ahern
7
0.48%
1
1.69%
Alexey Dobriyan
5
0.35%
2
3.39%
William Allen Simpson
4
0.28%
1
1.69%
Yuchung Cheng
3
0.21%
2
3.39%
Brian Haley
3
0.21%
1
1.69%
Octavian Purdila
1
0.07%
1
1.69%
Elena Reshetova
1
0.07%
1
1.69%
Total
1447
100.00%
59
100.00%
Directory: net/ipv6

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