net/ipv6/syncookies.c - kernel/msm-4.19 - Gitiles

 /*
  *  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]);
 }

 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));
 }

 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;
 }

 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);
 }
 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);
 }

 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;
 }
 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(skb, &tcp_opt, 0, NULL);

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

 	if (!cookie_timestamp_decode(&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) {
 		atomic_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.v64	= 0;
 	treq->rcv_isn = ntohl(th->seq) - 1;
 	treq->snt_isn = cookie;
 	treq->ts_off = 0;

 	/*
 	 * 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;
 }
	/*
	* 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]);
	}

	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));
	}

	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;
	}

	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);
	}
	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);
	}

	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;
	}
	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(skb, &tcp_opt, 0, NULL);

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

	if (!cookie_timestamp_decode(&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) {
	atomic_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.v64 = 0;
	treq->rcv_isn = ntohl(th->seq) - 1;
	treq->snt_isn = cookie;
	treq->ts_off = 0;

	/*
	* 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;
	}