tcp: TCP Fast Open Server - main code path
This patch adds the main processing path to complete the TFO server
patches.
A TFO request (i.e., SYN+data packet with a TFO cookie option) first
gets processed in tcp_v4_conn_request(). If it passes the various TFO
checks by tcp_fastopen_check(), a child socket will be created right
away to be accepted by applications, rather than waiting for the 3WHS
to finish.
In additon to the use of TFO cookie, a simple max_qlen based scheme
is put in place to fend off spoofed TFO attack.
When a valid ACK comes back to tcp_rcv_state_process(), it will cause
the state of the child socket to switch from either TCP_SYN_RECV to
TCP_ESTABLISHED, or TCP_FIN_WAIT1 to TCP_FIN_WAIT2. At this time
retransmission will resume for any unack'ed (data, FIN,...) segments.
Signed-off-by: H.K. Jerry Chu <hkchu@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index d47d5fe..8c304a4 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3127,6 +3127,12 @@
{
struct tcp_sock *tp = tcp_sk(sk);
+ /* If the retrans timer is currently being used by Fast Open
+ * for SYN-ACK retrans purpose, stay put.
+ */
+ if (tp->fastopen_rsk)
+ return;
+
if (!tp->packets_out) {
inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
} else {
@@ -5895,7 +5901,9 @@
tcp_send_synack(sk);
#if 0
/* Note, we could accept data and URG from this segment.
- * There are no obstacles to make this.
+ * There are no obstacles to make this (except that we must
+ * either change tcp_recvmsg() to prevent it from returning data
+ * before 3WHS completes per RFC793, or employ TCP Fast Open).
*
* However, if we ignore data in ACKless segments sometimes,
* we have no reasons to accept it sometimes.
@@ -5935,6 +5943,7 @@
{
struct tcp_sock *tp = tcp_sk(sk);
struct inet_connection_sock *icsk = inet_csk(sk);
+ struct request_sock *req;
int queued = 0;
tp->rx_opt.saw_tstamp = 0;
@@ -5990,7 +5999,14 @@
return 0;
}
- if (!tcp_validate_incoming(sk, skb, th, 0))
+ req = tp->fastopen_rsk;
+ if (req != NULL) {
+ BUG_ON(sk->sk_state != TCP_SYN_RECV &&
+ sk->sk_state != TCP_FIN_WAIT1);
+
+ if (tcp_check_req(sk, skb, req, NULL, true) == NULL)
+ goto discard;
+ } else if (!tcp_validate_incoming(sk, skb, th, 0))
return 0;
/* step 5: check the ACK field */
@@ -6000,7 +6016,22 @@
switch (sk->sk_state) {
case TCP_SYN_RECV:
if (acceptable) {
- tp->copied_seq = tp->rcv_nxt;
+ /* Once we leave TCP_SYN_RECV, we no longer
+ * need req so release it.
+ */
+ if (req) {
+ reqsk_fastopen_remove(sk, req, false);
+ } else {
+ /* Make sure socket is routed, for
+ * correct metrics.
+ */
+ icsk->icsk_af_ops->rebuild_header(sk);
+ tcp_init_congestion_control(sk);
+
+ tcp_mtup_init(sk);
+ tcp_init_buffer_space(sk);
+ tp->copied_seq = tp->rcv_nxt;
+ }
smp_mb();
tcp_set_state(sk, TCP_ESTABLISHED);
sk->sk_state_change(sk);
@@ -6022,23 +6053,27 @@
if (tp->rx_opt.tstamp_ok)
tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;
- /* Make sure socket is routed, for
- * correct metrics.
- */
- icsk->icsk_af_ops->rebuild_header(sk);
-
- tcp_init_metrics(sk);
-
- tcp_init_congestion_control(sk);
+ if (req) {
+ /* Re-arm the timer because data may
+ * have been sent out. This is similar
+ * to the regular data transmission case
+ * when new data has just been ack'ed.
+ *
+ * (TFO) - we could try to be more
+ * aggressive and retranmitting any data
+ * sooner based on when they were sent
+ * out.
+ */
+ tcp_rearm_rto(sk);
+ } else
+ tcp_init_metrics(sk);
/* Prevent spurious tcp_cwnd_restart() on
* first data packet.
*/
tp->lsndtime = tcp_time_stamp;
- tcp_mtup_init(sk);
tcp_initialize_rcv_mss(sk);
- tcp_init_buffer_space(sk);
tcp_fast_path_on(tp);
} else {
return 1;
@@ -6046,6 +6081,16 @@
break;
case TCP_FIN_WAIT1:
+ /* If we enter the TCP_FIN_WAIT1 state and we are a
+ * Fast Open socket and this is the first acceptable
+ * ACK we have received, this would have acknowledged
+ * our SYNACK so stop the SYNACK timer.
+ */
+ if (acceptable && req != NULL) {
+ /* We no longer need the request sock. */
+ reqsk_fastopen_remove(sk, req, false);
+ tcp_rearm_rto(sk);
+ }
if (tp->snd_una == tp->write_seq) {
struct dst_entry *dst;
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index bb148de..e64abed 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -352,6 +352,7 @@
const int code = icmp_hdr(icmp_skb)->code;
struct sock *sk;
struct sk_buff *skb;
+ struct request_sock *req;
__u32 seq;
__u32 remaining;
int err;
@@ -394,9 +395,12 @@
icsk = inet_csk(sk);
tp = tcp_sk(sk);
+ req = tp->fastopen_rsk;
seq = ntohl(th->seq);
if (sk->sk_state != TCP_LISTEN &&
- !between(seq, tp->snd_una, tp->snd_nxt)) {
+ !between(seq, tp->snd_una, tp->snd_nxt) &&
+ (req == NULL || seq != tcp_rsk(req)->snt_isn)) {
+ /* For a Fast Open socket, allow seq to be snt_isn. */
NET_INC_STATS_BH(net, LINUX_MIB_OUTOFWINDOWICMPS);
goto out;
}
@@ -435,6 +439,8 @@
!icsk->icsk_backoff)
break;
+ /* XXX (TFO) - revisit the following logic for TFO */
+
if (sock_owned_by_user(sk))
break;
@@ -466,6 +472,14 @@
goto out;
}
+ /* XXX (TFO) - if it's a TFO socket and has been accepted, rather
+ * than following the TCP_SYN_RECV case and closing the socket,
+ * we ignore the ICMP error and keep trying like a fully established
+ * socket. Is this the right thing to do?
+ */
+ if (req && req->sk == NULL)
+ goto out;
+
switch (sk->sk_state) {
struct request_sock *req, **prev;
case TCP_LISTEN:
@@ -498,7 +512,8 @@
case TCP_SYN_SENT:
case TCP_SYN_RECV: /* Cannot happen.
- It can f.e. if SYNs crossed.
+ It can f.e. if SYNs crossed,
+ or Fast Open.
*/
if (!sock_owned_by_user(sk)) {
sk->sk_err = err;
@@ -809,8 +824,12 @@
static void tcp_v4_reqsk_send_ack(struct sock *sk, struct sk_buff *skb,
struct request_sock *req)
{
- tcp_v4_send_ack(skb, tcp_rsk(req)->snt_isn + 1,
- tcp_rsk(req)->rcv_isn + 1, req->rcv_wnd,
+ /* sk->sk_state == TCP_LISTEN -> for regular TCP_SYN_RECV
+ * sk->sk_state == TCP_SYN_RECV -> for Fast Open.
+ */
+ tcp_v4_send_ack(skb, (sk->sk_state == TCP_LISTEN) ?
+ tcp_rsk(req)->snt_isn + 1 : tcp_sk(sk)->snd_nxt,
+ tcp_rsk(req)->rcv_nxt, req->rcv_wnd,
req->ts_recent,
0,
tcp_md5_do_lookup(sk, (union tcp_md5_addr *)&ip_hdr(skb)->daddr,
@@ -1272,6 +1291,178 @@
};
#endif
+static bool tcp_fastopen_check(struct sock *sk, struct sk_buff *skb,
+ struct request_sock *req,
+ struct tcp_fastopen_cookie *foc,
+ struct tcp_fastopen_cookie *valid_foc)
+{
+ bool skip_cookie = false;
+ struct fastopen_queue *fastopenq;
+
+ if (likely(!fastopen_cookie_present(foc))) {
+ /* See include/net/tcp.h for the meaning of these knobs */
+ if ((sysctl_tcp_fastopen & TFO_SERVER_ALWAYS) ||
+ ((sysctl_tcp_fastopen & TFO_SERVER_COOKIE_NOT_REQD) &&
+ (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq + 1)))
+ skip_cookie = true; /* no cookie to validate */
+ else
+ return false;
+ }
+ fastopenq = inet_csk(sk)->icsk_accept_queue.fastopenq;
+ /* A FO option is present; bump the counter. */
+ NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPFASTOPENPASSIVE);
+
+ /* 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.
+ */
+ if ((sysctl_tcp_fastopen & TFO_SERVER_ENABLE) == 0 ||
+ fastopenq == NULL || fastopenq->max_qlen == 0)
+ return false;
+
+ if (fastopenq->qlen >= fastopenq->max_qlen) {
+ struct request_sock *req1;
+ spin_lock(&fastopenq->lock);
+ req1 = fastopenq->rskq_rst_head;
+ if ((req1 == NULL) || time_after(req1->expires, jiffies)) {
+ spin_unlock(&fastopenq->lock);
+ NET_INC_STATS_BH(sock_net(sk),
+ LINUX_MIB_TCPFASTOPENLISTENOVERFLOW);
+ /* Avoid bumping LINUX_MIB_TCPFASTOPENPASSIVEFAIL*/
+ foc->len = -1;
+ return false;
+ }
+ fastopenq->rskq_rst_head = req1->dl_next;
+ fastopenq->qlen--;
+ spin_unlock(&fastopenq->lock);
+ reqsk_free(req1);
+ }
+ if (skip_cookie) {
+ tcp_rsk(req)->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
+ return true;
+ }
+ if (foc->len == TCP_FASTOPEN_COOKIE_SIZE) {
+ if ((sysctl_tcp_fastopen & TFO_SERVER_COOKIE_NOT_CHKED) == 0) {
+ tcp_fastopen_cookie_gen(ip_hdr(skb)->saddr, valid_foc);
+ if ((valid_foc->len != TCP_FASTOPEN_COOKIE_SIZE) ||
+ memcmp(&foc->val[0], &valid_foc->val[0],
+ TCP_FASTOPEN_COOKIE_SIZE) != 0)
+ return false;
+ valid_foc->len = -1;
+ }
+ /* Acknowledge the data received from the peer. */
+ tcp_rsk(req)->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
+ return true;
+ } else if (foc->len == 0) { /* Client requesting a cookie */
+ tcp_fastopen_cookie_gen(ip_hdr(skb)->saddr, valid_foc);
+ NET_INC_STATS_BH(sock_net(sk),
+ LINUX_MIB_TCPFASTOPENCOOKIEREQD);
+ } else {
+ /* Client sent a cookie with wrong size. Treat it
+ * the same as invalid and return a valid one.
+ */
+ tcp_fastopen_cookie_gen(ip_hdr(skb)->saddr, valid_foc);
+ }
+ return false;
+}
+
+static int tcp_v4_conn_req_fastopen(struct sock *sk,
+ struct sk_buff *skb,
+ struct sk_buff *skb_synack,
+ struct request_sock *req,
+ struct request_values *rvp)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue;
+ const struct inet_request_sock *ireq = inet_rsk(req);
+ struct sock *child;
+
+ req->retrans = 0;
+ req->sk = NULL;
+
+ child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL);
+ if (child == NULL) {
+ NET_INC_STATS_BH(sock_net(sk),
+ LINUX_MIB_TCPFASTOPENPASSIVEFAIL);
+ kfree_skb(skb_synack);
+ return -1;
+ }
+ ip_build_and_send_pkt(skb_synack, sk, ireq->loc_addr,
+ ireq->rmt_addr, ireq->opt);
+ /* XXX (TFO) - is it ok to ignore error and continue? */
+
+ 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);
+
+ tp->fastopen_rsk = req;
+ /* Do a hold on the listner sk so that if the listener is being
+ * closed, the child that has been accepted can live on and still
+ * access listen_lock.
+ */
+ sock_hold(sk);
+ tcp_rsk(req)->listener = sk;
+
+ /* RFC1323: The window in SYN & SYN/ACK segments is never
+ * scaled. So correct it appropriately.
+ */
+ tp->snd_wnd = ntohs(tcp_hdr(skb)->window);
+
+ /* Activate the retrans timer so that SYNACK can be retransmitted.
+ * The request socket is not added to the SYN table of the parent
+ * because it's been added to the accept queue directly.
+ */
+ inet_csk_reset_xmit_timer(child, ICSK_TIME_RETRANS,
+ TCP_TIMEOUT_INIT, TCP_RTO_MAX);
+
+ /* Add the child socket directly into the accept queue */
+ inet_csk_reqsk_queue_add(sk, req, child);
+
+ /* Now finish processing the fastopen child socket. */
+ inet_csk(child)->icsk_af_ops->rebuild_header(child);
+ tcp_init_congestion_control(child);
+ tcp_mtup_init(child);
+ tcp_init_buffer_space(child);
+ tcp_init_metrics(child);
+
+ /* Queue the data carried in the SYN packet. We need to first
+ * bump skb's refcnt because the caller will attempt to free it.
+ *
+ * XXX (TFO) - we honor a zero-payload TFO request for now.
+ * (Any reason not to?)
+ */
+ if (TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq + 1) {
+ /* Don't queue the skb if there is no payload in SYN.
+ * XXX (TFO) - How about SYN+FIN?
+ */
+ tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
+ } else {
+ skb = skb_get(skb);
+ skb_dst_drop(skb);
+ __skb_pull(skb, tcp_hdr(skb)->doff * 4);
+ skb_set_owner_r(skb, child);
+ __skb_queue_tail(&child->sk_receive_queue, skb);
+ tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
+ }
+ sk->sk_data_ready(sk, 0);
+ bh_unlock_sock(child);
+ sock_put(child);
+ WARN_ON(req->sk == NULL);
+ return 0;
+}
+
int tcp_v4_conn_request(struct sock *sk, struct sk_buff *skb)
{
struct tcp_extend_values tmp_ext;
@@ -1285,6 +1476,11 @@
__be32 daddr = ip_hdr(skb)->daddr;
__u32 isn = TCP_SKB_CB(skb)->when;
bool want_cookie = false;
+ struct flowi4 fl4;
+ struct tcp_fastopen_cookie foc = { .len = -1 };
+ struct tcp_fastopen_cookie valid_foc = { .len = -1 };
+ struct sk_buff *skb_synack;
+ int do_fastopen;
/* Never answer to SYNs send to broadcast or multicast */
if (skb_rtable(skb)->rt_flags & (RTCF_BROADCAST | RTCF_MULTICAST))
@@ -1319,7 +1515,8 @@
tcp_clear_options(&tmp_opt);
tmp_opt.mss_clamp = TCP_MSS_DEFAULT;
tmp_opt.user_mss = tp->rx_opt.user_mss;
- tcp_parse_options(skb, &tmp_opt, &hash_location, 0, NULL);
+ tcp_parse_options(skb, &tmp_opt, &hash_location, 0,
+ want_cookie ? NULL : &foc);
if (tmp_opt.cookie_plus > 0 &&
tmp_opt.saw_tstamp &&
@@ -1377,8 +1574,6 @@
isn = cookie_v4_init_sequence(sk, skb, &req->mss);
req->cookie_ts = tmp_opt.tstamp_ok;
} else if (!isn) {
- struct flowi4 fl4;
-
/* VJ's idea. We save last timestamp seen
* from the destination in peer table, when entering
* state TIME-WAIT, and check against it before
@@ -1419,14 +1614,52 @@
tcp_rsk(req)->snt_isn = isn;
tcp_rsk(req)->snt_synack = tcp_time_stamp;
- if (tcp_v4_send_synack(sk, dst, req,
- (struct request_values *)&tmp_ext,
- skb_get_queue_mapping(skb),
- want_cookie) ||
- want_cookie)
+ if (dst == NULL) {
+ dst = inet_csk_route_req(sk, &fl4, req);
+ if (dst == NULL)
+ goto drop_and_free;
+ }
+ do_fastopen = tcp_fastopen_check(sk, skb, req, &foc, &valid_foc);
+
+ /* We don't call tcp_v4_send_synack() directly because we need
+ * to make sure a child socket can be created successfully before
+ * sending back synack!
+ *
+ * XXX (TFO) - Ideally one would simply call tcp_v4_send_synack()
+ * (or better yet, call tcp_send_synack() in the child context
+ * directly, but will have to fix bunch of other code first)
+ * after syn_recv_sock() except one will need to first fix the
+ * latter to remove its dependency on the current implementation
+ * of tcp_v4_send_synack()->tcp_select_initial_window().
+ */
+ skb_synack = tcp_make_synack(sk, dst, req,
+ (struct request_values *)&tmp_ext,
+ fastopen_cookie_present(&valid_foc) ? &valid_foc : NULL);
+
+ if (skb_synack) {
+ __tcp_v4_send_check(skb_synack, ireq->loc_addr, ireq->rmt_addr);
+ skb_set_queue_mapping(skb_synack, skb_get_queue_mapping(skb));
+ } else
goto drop_and_free;
- inet_csk_reqsk_queue_hash_add(sk, req, TCP_TIMEOUT_INIT);
+ if (likely(!do_fastopen)) {
+ int err;
+ err = ip_build_and_send_pkt(skb_synack, sk, ireq->loc_addr,
+ ireq->rmt_addr, ireq->opt);
+ err = net_xmit_eval(err);
+ if (err || want_cookie)
+ goto drop_and_free;
+
+ tcp_rsk(req)->listener = NULL;
+ /* Add the request_sock to the SYN table */
+ inet_csk_reqsk_queue_hash_add(sk, req, TCP_TIMEOUT_INIT);
+ if (fastopen_cookie_present(&foc) && foc.len != 0)
+ NET_INC_STATS_BH(sock_net(sk),
+ LINUX_MIB_TCPFASTOPENPASSIVEFAIL);
+ } else if (tcp_v4_conn_req_fastopen(sk, skb, skb_synack, req,
+ (struct request_values *)&tmp_ext))
+ goto drop_and_free;
+
return 0;
drop_and_release:
@@ -1977,6 +2210,7 @@
tcp_cookie_values_release);
tp->cookie_values = NULL;
}
+ BUG_ON(tp->fastopen_rsk != NULL);
/* If socket is aborted during connect operation */
tcp_free_fastopen_req(tp);
@@ -2425,6 +2659,7 @@
const struct tcp_sock *tp = tcp_sk(sk);
const struct inet_connection_sock *icsk = inet_csk(sk);
const struct inet_sock *inet = inet_sk(sk);
+ struct fastopen_queue *fastopenq = icsk->icsk_accept_queue.fastopenq;
__be32 dest = inet->inet_daddr;
__be32 src = inet->inet_rcv_saddr;
__u16 destp = ntohs(inet->inet_dport);
@@ -2469,7 +2704,9 @@
jiffies_to_clock_t(icsk->icsk_ack.ato),
(icsk->icsk_ack.quick << 1) | icsk->icsk_ack.pingpong,
tp->snd_cwnd,
- tcp_in_initial_slowstart(tp) ? -1 : tp->snd_ssthresh,
+ sk->sk_state == TCP_LISTEN ?
+ (fastopenq ? fastopenq->max_qlen : 0) :
+ (tcp_in_initial_slowstart(tp) ? -1 : tp->snd_ssthresh),
len);
}