// SPDX-License-Identifier: GPL-2.0-or-later/* *  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 */ #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>#include <net/tcp_ecn.h> #define COOKIEBITS 24	/* Upper bits store count */#define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1) static siphash_aligned_key_t syncookie6_secret[2]; /* 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 = ntohl(th->ack_seq) - 1;	__u32 seq = ntohl(th->seq) - 1;	__u32 mssind; 	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); static struct request_sock *cookie_tcp_check(struct net *net, struct sock *sk,					     struct sk_buff *skb){	struct tcp_options_received tcp_opt;	u32 tsoff = 0;	int mss; 	if (tcp_synq_no_recent_overflow(sk))		goto out; 	mss = __cookie_v6_check(ipv6_hdr(skb), tcp_hdr(skb));	if (!mss) {		__NET_INC_STATS(net, LINUX_MIB_SYNCOOKIESFAILED);		goto out;	} 	__NET_INC_STATS(net, LINUX_MIB_SYNCOOKIESRECV); 	/* check for timestamp cookie support */	memset(&tcp_opt, 0, sizeof(tcp_opt));	tcp_parse_options(net, skb, &tcp_opt, 0, NULL); 	if (tcp_opt.saw_tstamp && tcp_opt.rcv_tsecr) {		union tcp_seq_and_ts_off st; 		st = secure_tcpv6_seq_and_ts_off(net,						 ipv6_hdr(skb)->daddr.s6_addr32,						 ipv6_hdr(skb)->saddr.s6_addr32,						 tcp_hdr(skb)->dest,						 tcp_hdr(skb)->source);		tsoff = st.ts_off;		tcp_opt.rcv_tsecr -= tsoff;	} 	if (!cookie_timestamp_decode(net, &tcp_opt))		goto out; 	return cookie_tcp_reqsk_alloc(&tcp6_request_sock_ops, sk, skb,				      &tcp_opt, mss, tsoff);out:	return ERR_PTR(-EINVAL);} struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb){	const struct tcphdr *th = tcp_hdr(skb);	struct ipv6_pinfo *np = inet6_sk(sk);	struct tcp_sock *tp = tcp_sk(sk);	struct inet_request_sock *ireq;	struct net *net = sock_net(sk);	struct request_sock *req;	struct dst_entry *dst;	struct sock *ret = sk;	__u8 rcv_wscale;	int full_space;	SKB_DR(reason); 	if (!READ_ONCE(net->ipv4.sysctl_tcp_syncookies) ||	    !th->ack || th->rst)		goto out; 	if (cookie_bpf_ok(skb)) {		req = cookie_bpf_check(sk, skb);	} else {		req = cookie_tcp_check(net, sk, skb);		if (IS_ERR(req))			goto out;	}	if (!req) {		SKB_DR_SET(reason, NO_SOCKET);		goto out_drop;	} 	ireq = inet_rsk(req); 	ireq->ir_v6_rmt_addr = ipv6_hdr(skb)->saddr;	ireq->ir_v6_loc_addr = ipv6_hdr(skb)->daddr; 	if (security_inet_conn_request(sk, skb, req)) {		SKB_DR_SET(reason, SECURITY_HOOK);		goto out_free;	} 	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;	} 	/* 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); 	tcp_ao_syncookie(sk, skb, req, AF_INET6); 	/*	 * 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_uid(sk);		security_req_classify_flow(req, flowi6_to_flowi_common(&fl6)); 		ip6_ecmp_set_mp_hash(net, &fl6, tcp_rsk(req)->txhash); 		dst = ip6_dst_lookup_flow(net, sk, &fl6, final_p);		if (IS_ERR(dst)) {			SKB_DR_SET(reason, IP_OUTNOROUTES);			goto out_free;		}	} 	req->rsk_window_clamp = READ_ONCE(tp->window_clamp) ? :dst_metric(dst, RTAX_WINDOW);	/* limit the window selection if the user enforce a smaller rx buffer */	full_space = tcp_full_space(sk);	if (sk->sk_userlocks & SOCK_RCVBUF_LOCK &&	    (req->rsk_window_clamp > full_space || req->rsk_window_clamp == 0))		req->rsk_window_clamp = full_space; 	tcp_select_initial_window(sk, full_space, req->mss,				  &req->rsk_rcv_wnd, &req->rsk_window_clamp,				  ireq->wscale_ok, &rcv_wscale,				  dst_metric(dst, RTAX_INITRWND)); 	/* req->syncookie is set true only if ACK is validated	 * by BPF kfunc, then, rcv_wscale is already configured.	 */	if (!req->syncookie)		ireq->rcv_wscale = rcv_wscale;	ireq->ecn_ok &= cookie_ecn_ok(net, dst);	tcp_rsk(req)->accecn_ok = ireq->ecn_ok && cookie_accecn_ok(th); 	ret = tcp_get_cookie_sock(sk, skb, req, dst);	if (!ret) {		SKB_DR_SET(reason, NO_SOCKET);		goto out_drop;	}out:	return ret;out_free:	reqsk_free(req);out_drop:	sk_skb_reason_drop(sk, skb, reason);	return NULL;}