1 files changed, 267 insertions, 0 deletions
diff --git a/net/ipv6/syncookies.c b/net/ipv6/syncookies.c
new file mode 100644
index 000000000..c10a68bb8
--- /dev/null
+++ b/net/ipv6/syncookies.c
@@ -0,0 +1,267 @@
+// 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>
+
+#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 full_space, mss;
+	struct dst_entry *dst;
+	__u8 rcv_wscale;
+	u32 tsoff = 0;
+
+	if (!READ_ONCE(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 = cookie_tcp_reqsk_alloc(&tcp6_request_sock_ops,
+				     &tcp_request_sock_ipv6_ops, sk, skb);
+	if (!req)
+		goto out;
+
+	ireq = inet_rsk(req);
+	treq = tcp_rsk(req);
+	treq->tfo_listener = false;
+
+	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 (security_inet_conn_request(sk, skb, req))
+		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;
+	}
+
+	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();
+	if (IS_ENABLED(CONFIG_SMC))
+		ireq->smc_ok = 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_common(&fl6));
+
+		dst = ip6_dst_lookup_flow(sock_net(sk), sk, &fl6, final_p);
+		if (IS_ERR(dst))
+			goto out_free;
+	}
+
+	req->rsk_window_clamp = 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));
+
+	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;
+}