1 files changed, 595 insertions, 0 deletions

diff --git a/net/ipv4/tcp_fastopen.c b/net/ipv4/tcp_fastopen.c
new file mode 100644
index 000000000..8ed54e733
--- /dev/null
+++ b/net/ipv4/tcp_fastopen.c
@@ -0,0 +1,595 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/kernel.h>
+#include <linux/tcp.h>
+#include <linux/rcupdate.h>
+#include <net/tcp.h>
+
+void tcp_fastopen_init_key_once(struct net *net)
+{
+	u8 key[TCP_FASTOPEN_KEY_LENGTH];
+	struct tcp_fastopen_context *ctxt;
+
+	rcu_read_lock();
+	ctxt = rcu_dereference(net->ipv4.tcp_fastopen_ctx);
+	if (ctxt) {
+		rcu_read_unlock();
+		return;
+	}
+	rcu_read_unlock();
+
+	/* tcp_fastopen_reset_cipher publishes the new context
+	 * atomically, so we allow this race happening here.
+	 *
+	 * All call sites of tcp_fastopen_cookie_gen also check
+	 * for a valid cookie, so this is an acceptable risk.
+	 */
+	get_random_bytes(key, sizeof(key));
+	tcp_fastopen_reset_cipher(net, NULL, key, NULL);
+}
+
+static void tcp_fastopen_ctx_free(struct rcu_head *head)
+{
+	struct tcp_fastopen_context *ctx =
+	    container_of(head, struct tcp_fastopen_context, rcu);
+
+	kfree_sensitive(ctx);
+}
+
+void tcp_fastopen_destroy_cipher(struct sock *sk)
+{
+	struct tcp_fastopen_context *ctx;
+
+	ctx = rcu_dereference_protected(
+			inet_csk(sk)->icsk_accept_queue.fastopenq.ctx, 1);
+	if (ctx)
+		call_rcu(&ctx->rcu, tcp_fastopen_ctx_free);
+}
+
+void tcp_fastopen_ctx_destroy(struct net *net)
+{
+	struct tcp_fastopen_context *ctxt;
+
+	ctxt = xchg((__force struct tcp_fastopen_context **)&net->ipv4.tcp_fastopen_ctx, NULL);
+
+	if (ctxt)
+		call_rcu(&ctxt->rcu, tcp_fastopen_ctx_free);
+}
+
+int tcp_fastopen_reset_cipher(struct net *net, struct sock *sk,
+			      void *primary_key, void *backup_key)
+{
+	struct tcp_fastopen_context *ctx, *octx;
+	struct fastopen_queue *q;
+	int err = 0;
+
+	ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
+	if (!ctx) {
+		err = -ENOMEM;
+		goto out;
+	}
+
+	ctx->key[0].key[0] = get_unaligned_le64(primary_key);
+	ctx->key[0].key[1] = get_unaligned_le64(primary_key + 8);
+	if (backup_key) {
+		ctx->key[1].key[0] = get_unaligned_le64(backup_key);
+		ctx->key[1].key[1] = get_unaligned_le64(backup_key + 8);
+		ctx->num = 2;
+	} else {
+		ctx->num = 1;
+	}
+
+	if (sk) {
+		q = &inet_csk(sk)->icsk_accept_queue.fastopenq;
+		octx = xchg((__force struct tcp_fastopen_context **)&q->ctx, ctx);
+	} else {
+		octx = xchg((__force struct tcp_fastopen_context **)&net->ipv4.tcp_fastopen_ctx, ctx);
+	}
+
+	if (octx)
+		call_rcu(&octx->rcu, tcp_fastopen_ctx_free);
+out:
+	return err;
+}
+
+int tcp_fastopen_get_cipher(struct net *net, struct inet_connection_sock *icsk,
+			    u64 *key)
+{
+	struct tcp_fastopen_context *ctx;
+	int n_keys = 0, i;
+
+	rcu_read_lock();
+	if (icsk)
+		ctx = rcu_dereference(icsk->icsk_accept_queue.fastopenq.ctx);
+	else
+		ctx = rcu_dereference(net->ipv4.tcp_fastopen_ctx);
+	if (ctx) {
+		n_keys = tcp_fastopen_context_len(ctx);
+		for (i = 0; i < n_keys; i++) {
+			put_unaligned_le64(ctx->key[i].key[0], key + (i * 2));
+			put_unaligned_le64(ctx->key[i].key[1], key + (i * 2) + 1);
+		}
+	}
+	rcu_read_unlock();
+
+	return n_keys;
+}
+
+static bool __tcp_fastopen_cookie_gen_cipher(struct request_sock *req,
+					     struct sk_buff *syn,
+					     const siphash_key_t *key,
+					     struct tcp_fastopen_cookie *foc)
+{
+	BUILD_BUG_ON(TCP_FASTOPEN_COOKIE_SIZE != sizeof(u64));
+
+	if (req->rsk_ops->family == AF_INET) {
+		const struct iphdr *iph = ip_hdr(syn);
+
+		foc->val[0] = cpu_to_le64(siphash(&iph->saddr,
+					  sizeof(iph->saddr) +
+					  sizeof(iph->daddr),
+					  key));
+		foc->len = TCP_FASTOPEN_COOKIE_SIZE;
+		return true;
+	}
+#if IS_ENABLED(CONFIG_IPV6)
+	if (req->rsk_ops->family == AF_INET6) {
+		const struct ipv6hdr *ip6h = ipv6_hdr(syn);
+
+		foc->val[0] = cpu_to_le64(siphash(&ip6h->saddr,
+					  sizeof(ip6h->saddr) +
+					  sizeof(ip6h->daddr),
+					  key));
+		foc->len = TCP_FASTOPEN_COOKIE_SIZE;
+		return true;
+	}
+#endif
+	return false;
+}
+
+/* Generate the fastopen cookie by applying SipHash to both the source and
+ * destination addresses.
+ */
+static void tcp_fastopen_cookie_gen(struct sock *sk,
+				    struct request_sock *req,
+				    struct sk_buff *syn,
+				    struct tcp_fastopen_cookie *foc)
+{
+	struct tcp_fastopen_context *ctx;
+
+	rcu_read_lock();
+	ctx = tcp_fastopen_get_ctx(sk);
+	if (ctx)
+		__tcp_fastopen_cookie_gen_cipher(req, syn, &ctx->key[0], foc);
+	rcu_read_unlock();
+}
+
+/* If an incoming SYN or SYNACK frame contains a payload and/or FIN,
+ * queue this additional data / FIN.
+ */
+void tcp_fastopen_add_skb(struct sock *sk, struct sk_buff *skb)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+
+	if (TCP_SKB_CB(skb)->end_seq == tp->rcv_nxt)
+		return;
+
+	skb = skb_clone(skb, GFP_ATOMIC);
+	if (!skb)
+		return;
+
+	skb_dst_drop(skb);
+	/* segs_in has been initialized to 1 in tcp_create_openreq_child().
+	 * Hence, reset segs_in to 0 before calling tcp_segs_in()
+	 * to avoid double counting.  Also, tcp_segs_in() expects
+	 * skb->len to include the tcp_hdrlen.  Hence, it should
+	 * be called before __skb_pull().
+	 */
+	tp->segs_in = 0;
+	tcp_segs_in(tp, skb);
+	__skb_pull(skb, tcp_hdrlen(skb));
+	sk_forced_mem_schedule(sk, skb->truesize);
+	skb_set_owner_r(skb, sk);
+
+	TCP_SKB_CB(skb)->seq++;
+	TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_SYN;
+
+	tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
+	__skb_queue_tail(&sk->sk_receive_queue, skb);
+	tp->syn_data_acked = 1;
+
+	/* u64_stats_update_begin(&tp->syncp) not needed here,
+	 * as we certainly are not changing upper 32bit value (0)
+	 */
+	tp->bytes_received = skb->len;
+
+	if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
+		tcp_fin(sk);
+}
+
+/* returns 0 - no key match, 1 for primary, 2 for backup */
+static int tcp_fastopen_cookie_gen_check(struct sock *sk,
+					 struct request_sock *req,
+					 struct sk_buff *syn,
+					 struct tcp_fastopen_cookie *orig,
+					 struct tcp_fastopen_cookie *valid_foc)
+{
+	struct tcp_fastopen_cookie search_foc = { .len = -1 };
+	struct tcp_fastopen_cookie *foc = valid_foc;
+	struct tcp_fastopen_context *ctx;
+	int i, ret = 0;
+
+	rcu_read_lock();
+	ctx = tcp_fastopen_get_ctx(sk);
+	if (!ctx)
+		goto out;
+	for (i = 0; i < tcp_fastopen_context_len(ctx); i++) {
+		__tcp_fastopen_cookie_gen_cipher(req, syn, &ctx->key[i], foc);
+		if (tcp_fastopen_cookie_match(foc, orig)) {
+			ret = i + 1;
+			goto out;
+		}
+		foc = &search_foc;
+	}
+out:
+	rcu_read_unlock();
+	return ret;
+}
+
+static struct sock *tcp_fastopen_create_child(struct sock *sk,
+					      struct sk_buff *skb,
+					      struct request_sock *req)
+{
+	struct tcp_sock *tp;
+	struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue;
+	struct sock *child;
+	bool own_req;
+
+	child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL,
+							 NULL, &own_req);
+	if (!child)
+		return NULL;
+
+	spin_lock(&queue->fastopenq.lock);
+	queue->fastopenq.qlen++;
+	spin_unlock(&queue->fastopenq.lock);
+
+	/* Initialize the child socket. Have to fix some values to take
+	 * into account the child is a Fast Open socket and is created
+	 * only out of the bits carried in the SYN packet.
+	 */
+	tp = tcp_sk(child);
+
+	rcu_assign_pointer(tp->fastopen_rsk, req);
+	tcp_rsk(req)->tfo_listener = true;
+
+	/* RFC1323: The window in SYN & SYN/ACK segments is never
+	 * scaled. So correct it appropriately.
+	 */
+	tp->snd_wnd = ntohs(tcp_hdr(skb)->window);
+	tp->max_window = tp->snd_wnd;
+
+	/* Activate the retrans timer so that SYNACK can be retransmitted.
+	 * The request socket is not added to the ehash
+	 * because it's been added to the accept queue directly.
+	 */
+	req->timeout = tcp_timeout_init(child);
+	inet_csk_reset_xmit_timer(child, ICSK_TIME_RETRANS,
+				  req->timeout, TCP_RTO_MAX);
+
+	refcount_set(&req->rsk_refcnt, 2);
+
+	/* Now finish processing the fastopen child socket. */
+	tcp_init_transfer(child, BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB, skb);
+
+	tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
+
+	tcp_fastopen_add_skb(child, skb);
+
+	tcp_rsk(req)->rcv_nxt = tp->rcv_nxt;
+	tp->rcv_wup = tp->rcv_nxt;
+	/* tcp_conn_request() is sending the SYNACK,
+	 * and queues the child into listener accept queue.
+	 */
+	return child;
+}
+
+static bool tcp_fastopen_queue_check(struct sock *sk)
+{
+	struct fastopen_queue *fastopenq;
+	int max_qlen;
+
+	/* Make sure the listener has enabled fastopen, and we don't
+	 * exceed the max # of pending TFO requests allowed before trying
+	 * to validating the cookie in order to avoid burning CPU cycles
+	 * unnecessarily.
+	 *
+	 * XXX (TFO) - The implication of checking the max_qlen before
+	 * processing a cookie request is that clients can't differentiate
+	 * between qlen overflow causing Fast Open to be disabled
+	 * temporarily vs a server not supporting Fast Open at all.
+	 */
+	fastopenq = &inet_csk(sk)->icsk_accept_queue.fastopenq;
+	max_qlen = READ_ONCE(fastopenq->max_qlen);
+	if (max_qlen == 0)
+		return false;
+
+	if (fastopenq->qlen >= max_qlen) {
+		struct request_sock *req1;
+		spin_lock(&fastopenq->lock);
+		req1 = fastopenq->rskq_rst_head;
+		if (!req1 || time_after(req1->rsk_timer.expires, jiffies)) {
+			__NET_INC_STATS(sock_net(sk),
+					LINUX_MIB_TCPFASTOPENLISTENOVERFLOW);
+			spin_unlock(&fastopenq->lock);
+			return false;
+		}
+		fastopenq->rskq_rst_head = req1->dl_next;
+		fastopenq->qlen--;
+		spin_unlock(&fastopenq->lock);
+		reqsk_put(req1);
+	}
+	return true;
+}
+
+static bool tcp_fastopen_no_cookie(const struct sock *sk,
+				   const struct dst_entry *dst,
+				   int flag)
+{
+	return (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_fastopen) & flag) ||
+	       tcp_sk(sk)->fastopen_no_cookie ||
+	       (dst && dst_metric(dst, RTAX_FASTOPEN_NO_COOKIE));
+}
+
+/* Returns true if we should perform Fast Open on the SYN. The cookie (foc)
+ * may be updated and return the client in the SYN-ACK later. E.g., Fast Open
+ * cookie request (foc->len == 0).
+ */
+struct sock *tcp_try_fastopen(struct sock *sk, struct sk_buff *skb,
+			      struct request_sock *req,
+			      struct tcp_fastopen_cookie *foc,
+			      const struct dst_entry *dst)
+{
+	bool syn_data = TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq + 1;
+	int tcp_fastopen = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_fastopen);
+	struct tcp_fastopen_cookie valid_foc = { .len = -1 };
+	struct sock *child;
+	int ret = 0;
+
+	if (foc->len == 0) /* Client requests a cookie */
+		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENCOOKIEREQD);
+
+	if (!((tcp_fastopen & TFO_SERVER_ENABLE) &&
+	      (syn_data || foc->len >= 0) &&
+	      tcp_fastopen_queue_check(sk))) {
+		foc->len = -1;
+		return NULL;
+	}
+
+	if (tcp_fastopen_no_cookie(sk, dst, TFO_SERVER_COOKIE_NOT_REQD))
+		goto fastopen;
+
+	if (foc->len == 0) {
+		/* Client requests a cookie. */
+		tcp_fastopen_cookie_gen(sk, req, skb, &valid_foc);
+	} else if (foc->len > 0) {
+		ret = tcp_fastopen_cookie_gen_check(sk, req, skb, foc,
+						    &valid_foc);
+		if (!ret) {
+			NET_INC_STATS(sock_net(sk),
+				      LINUX_MIB_TCPFASTOPENPASSIVEFAIL);
+		} else {
+			/* Cookie is valid. Create a (full) child socket to
+			 * accept the data in SYN before returning a SYN-ACK to
+			 * ack the data. If we fail to create the socket, fall
+			 * back and ack the ISN only but includes the same
+			 * cookie.
+			 *
+			 * Note: Data-less SYN with valid cookie is allowed to
+			 * send data in SYN_RECV state.
+			 */
+fastopen:
+			child = tcp_fastopen_create_child(sk, skb, req);
+			if (child) {
+				if (ret == 2) {
+					valid_foc.exp = foc->exp;
+					*foc = valid_foc;
+					NET_INC_STATS(sock_net(sk),
+						      LINUX_MIB_TCPFASTOPENPASSIVEALTKEY);
+				} else {
+					foc->len = -1;
+				}
+				NET_INC_STATS(sock_net(sk),
+					      LINUX_MIB_TCPFASTOPENPASSIVE);
+				return child;
+			}
+			NET_INC_STATS(sock_net(sk),
+				      LINUX_MIB_TCPFASTOPENPASSIVEFAIL);
+		}
+	}
+	valid_foc.exp = foc->exp;
+	*foc = valid_foc;
+	return NULL;
+}
+
+bool tcp_fastopen_cookie_check(struct sock *sk, u16 *mss,
+			       struct tcp_fastopen_cookie *cookie)
+{
+	const struct dst_entry *dst;
+
+	tcp_fastopen_cache_get(sk, mss, cookie);
+
+	/* Firewall blackhole issue check */
+	if (tcp_fastopen_active_should_disable(sk)) {
+		cookie->len = -1;
+		return false;
+	}
+
+	dst = __sk_dst_get(sk);
+
+	if (tcp_fastopen_no_cookie(sk, dst, TFO_CLIENT_NO_COOKIE)) {
+		cookie->len = -1;
+		return true;
+	}
+	if (cookie->len > 0)
+		return true;
+	tcp_sk(sk)->fastopen_client_fail = TFO_COOKIE_UNAVAILABLE;
+	return false;
+}
+
+/* This function checks if we want to defer sending SYN until the first
+ * write().  We defer under the following conditions:
+ * 1. fastopen_connect sockopt is set
+ * 2. we have a valid cookie
+ * Return value: return true if we want to defer until application writes data
+ *               return false if we want to send out SYN immediately
+ */
+bool tcp_fastopen_defer_connect(struct sock *sk, int *err)
+{
+	struct tcp_fastopen_cookie cookie = { .len = 0 };
+	struct tcp_sock *tp = tcp_sk(sk);
+	u16 mss;
+
+	if (tp->fastopen_connect && !tp->fastopen_req) {
+		if (tcp_fastopen_cookie_check(sk, &mss, &cookie)) {
+			inet_set_bit(DEFER_CONNECT, sk);
+			return true;
+		}
+
+		/* Alloc fastopen_req in order for FO option to be included
+		 * in SYN
+		 */
+		tp->fastopen_req = kzalloc(sizeof(*tp->fastopen_req),
+					   sk->sk_allocation);
+		if (tp->fastopen_req)
+			tp->fastopen_req->cookie = cookie;
+		else
+			*err = -ENOBUFS;
+	}
+	return false;
+}
+EXPORT_SYMBOL(tcp_fastopen_defer_connect);
+
+/*
+ * The following code block is to deal with middle box issues with TFO:
+ * Middlebox firewall issues can potentially cause server's data being
+ * blackholed after a successful 3WHS using TFO.
+ * The proposed solution is to disable active TFO globally under the
+ * following circumstances:
+ *   1. client side TFO socket receives out of order FIN
+ *   2. client side TFO socket receives out of order RST
+ *   3. client side TFO socket has timed out three times consecutively during
+ *      or after handshake
+ * We disable active side TFO globally for 1hr at first. Then if it
+ * happens again, we disable it for 2h, then 4h, 8h, ...
+ * And we reset the timeout back to 1hr when we see a successful active
+ * TFO connection with data exchanges.
+ */
+
+/* Disable active TFO and record current jiffies and
+ * tfo_active_disable_times
+ */
+void tcp_fastopen_active_disable(struct sock *sk)
+{
+	struct net *net = sock_net(sk);
+
+	if (!READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_fastopen_blackhole_timeout))
+		return;
+
+	/* Paired with READ_ONCE() in tcp_fastopen_active_should_disable() */
+	WRITE_ONCE(net->ipv4.tfo_active_disable_stamp, jiffies);
+
+	/* Paired with smp_rmb() in tcp_fastopen_active_should_disable().
+	 * We want net->ipv4.tfo_active_disable_stamp to be updated first.
+	 */
+	smp_mb__before_atomic();
+	atomic_inc(&net->ipv4.tfo_active_disable_times);
+
+	NET_INC_STATS(net, LINUX_MIB_TCPFASTOPENBLACKHOLE);
+}
+
+/* Calculate timeout for tfo active disable
+ * Return true if we are still in the active TFO disable period
+ * Return false if timeout already expired and we should use active TFO
+ */
+bool tcp_fastopen_active_should_disable(struct sock *sk)
+{
+	unsigned int tfo_bh_timeout =
+		READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_fastopen_blackhole_timeout);
+	unsigned long timeout;
+	int tfo_da_times;
+	int multiplier;
+
+	if (!tfo_bh_timeout)
+		return false;
+
+	tfo_da_times = atomic_read(&sock_net(sk)->ipv4.tfo_active_disable_times);
+	if (!tfo_da_times)
+		return false;
+
+	/* Paired with smp_mb__before_atomic() in tcp_fastopen_active_disable() */
+	smp_rmb();
+
+	/* Limit timeout to max: 2^6 * initial timeout */
+	multiplier = 1 << min(tfo_da_times - 1, 6);
+
+	/* Paired with the WRITE_ONCE() in tcp_fastopen_active_disable(). */
+	timeout = READ_ONCE(sock_net(sk)->ipv4.tfo_active_disable_stamp) +
+		  multiplier * tfo_bh_timeout * HZ;
+	if (time_before(jiffies, timeout))
+		return true;
+
+	/* Mark check bit so we can check for successful active TFO
+	 * condition and reset tfo_active_disable_times
+	 */
+	tcp_sk(sk)->syn_fastopen_ch = 1;
+	return false;
+}
+
+/* Disable active TFO if FIN is the only packet in the ofo queue
+ * and no data is received.
+ * Also check if we can reset tfo_active_disable_times if data is
+ * received successfully on a marked active TFO sockets opened on
+ * a non-loopback interface
+ */
+void tcp_fastopen_active_disable_ofo_check(struct sock *sk)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	struct dst_entry *dst;
+	struct sk_buff *skb;
+
+	if (!tp->syn_fastopen)
+		return;
+
+	if (!tp->data_segs_in) {
+		skb = skb_rb_first(&tp->out_of_order_queue);
+		if (skb && !skb_rb_next(skb)) {
+			if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) {
+				tcp_fastopen_active_disable(sk);
+				return;
+			}
+		}
+	} else if (tp->syn_fastopen_ch &&
+		   atomic_read(&sock_net(sk)->ipv4.tfo_active_disable_times)) {
+		dst = sk_dst_get(sk);
+		if (!(dst && dst->dev && (dst->dev->flags & IFF_LOOPBACK)))
+			atomic_set(&sock_net(sk)->ipv4.tfo_active_disable_times, 0);
+		dst_release(dst);
+	}
+}
+
+void tcp_fastopen_active_detect_blackhole(struct sock *sk, bool expired)
+{
+	u32 timeouts = inet_csk(sk)->icsk_retransmits;
+	struct tcp_sock *tp = tcp_sk(sk);
+
+	/* Broken middle-boxes may black-hole Fast Open connection during or
+	 * even after the handshake. Be extremely conservative and pause
+	 * Fast Open globally after hitting the third consecutive timeout or
+	 * exceeding the configured timeout limit.
+	 */
+	if ((tp->syn_fastopen || tp->syn_data || tp->syn_data_acked) &&
+	    (timeouts == 2 || (timeouts < 2 && expired))) {
+		tcp_fastopen_active_disable(sk);
+		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENACTIVEFAIL);
+	}
+}