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authorWei Wang <weiwan@google.com>2017-04-20 14:45:46 -0700
committerDavid S. Miller <davem@davemloft.net>2017-04-24 14:27:17 -0400
commitcf1ef3f0719b4dcb74810ed507e2a2540f9811b4 (patch)
tree1b070be7a31eb3557e7f0701a6aca667b1eb13dd /net
parentMerge tag 'mlx5-updates-2017-04-22' of git://git.kernel.org/pub/scm/linux/kernel/git/saeed/linux (diff)
downloadlinux-dev-cf1ef3f0719b4dcb74810ed507e2a2540f9811b4.tar.xz
linux-dev-cf1ef3f0719b4dcb74810ed507e2a2540f9811b4.zip
net/tcp_fastopen: Disable active side TFO in certain scenarios
Middlebox firewall issues can potentially cause server's data being blackholed after a successful 3WHS using TFO. Following are the related reports from Apple: https://www.nanog.org/sites/default/files/Paasch_Network_Support.pdf Slide 31 identifies an issue where the client ACK to the server's data sent during a TFO'd handshake is dropped. C ---> syn-data ---> S C <--- syn/ack ----- S C (accept & write) C <---- data ------- S C ----- ACK -> X S [retry and timeout] https://www.ietf.org/proceedings/94/slides/slides-94-tcpm-13.pdf Slide 5 shows a similar situation that the server's data gets dropped after 3WHS. C ---- syn-data ---> S C <--- syn/ack ----- S C ---- ack --------> S S (accept & write) C? X <- data ------ S [retry and timeout] This is the worst failure b/c the client can not detect such behavior to mitigate the situation (such as disabling TFO). Failing to proceed, the application (e.g., SSL library) may simply timeout and retry with TFO again, and the process repeats indefinitely. The proposed solution is to disable active TFO globally under the following circumstances: 1. client side TFO socket detects out of order FIN 2. client side TFO socket receives out of order RST 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 to 1hr if a client side TFO sockets not opened on loopback has successfully received data segs from server. And we examine this condition during close(). The rational behind it is that when such firewall issue happens, application running on the client should eventually close the socket as it is not able to get the data it is expecting. Or application running on the server should close the socket as it is not able to receive any response from client. In both cases, out of order FIN or RST will get received on the client given that the firewall will not block them as no data are in those frames. And we want to disable active TFO globally as it helps if the middle box is very close to the client and most of the connections are likely to fail. Also, add a debug sysctl: tcp_fastopen_blackhole_detect_timeout_sec: the initial timeout to use when firewall blackhole issue happens. This can be set and read. When setting it to 0, it means to disable the active disable logic. Signed-off-by: Wei Wang <weiwan@google.com> Acked-by: Yuchung Cheng <ycheng@google.com> Acked-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net')
-rw-r--r--net/ipv4/sysctl_net_ipv4.c21
-rw-r--r--net/ipv4/tcp.c1
-rw-r--r--net/ipv4/tcp_fastopen.c101
-rw-r--r--net/ipv4/tcp_input.c23
-rw-r--r--net/ipv4/tcp_ipv4.c3
5 files changed, 145 insertions, 4 deletions
diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index ddac9e64b702..86957e9cd6c6 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -350,6 +350,19 @@ static int proc_udp_early_demux(struct ctl_table *table, int write,
return ret;
}
+static int proc_tfo_blackhole_detect_timeout(struct ctl_table *table,
+ int write,
+ void __user *buffer,
+ size_t *lenp, loff_t *ppos)
+{
+ int ret;
+
+ ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
+ if (write && ret == 0)
+ tcp_fastopen_active_timeout_reset();
+ return ret;
+}
+
static struct ctl_table ipv4_table[] = {
{
.procname = "tcp_timestamps",
@@ -400,6 +413,14 @@ static struct ctl_table ipv4_table[] = {
.proc_handler = proc_tcp_fastopen_key,
},
{
+ .procname = "tcp_fastopen_blackhole_timeout_sec",
+ .data = &sysctl_tcp_fastopen_blackhole_timeout,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = proc_tfo_blackhole_detect_timeout,
+ .extra1 = &zero,
+ },
+ {
.procname = "tcp_abort_on_overflow",
.data = &sysctl_tcp_abort_on_overflow,
.maxlen = sizeof(int),
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 04843ae77b9e..efc976ae66ae 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2296,6 +2296,7 @@ int tcp_disconnect(struct sock *sk, int flags)
tcp_clear_xmit_timers(sk);
__skb_queue_purge(&sk->sk_receive_queue);
tcp_write_queue_purge(sk);
+ tcp_fastopen_active_disable_ofo_check(sk);
skb_rbtree_purge(&tp->out_of_order_queue);
inet->inet_dport = 0;
diff --git a/net/ipv4/tcp_fastopen.c b/net/ipv4/tcp_fastopen.c
index 8ea4e9787f82..ff2d30ffc6f3 100644
--- a/net/ipv4/tcp_fastopen.c
+++ b/net/ipv4/tcp_fastopen.c
@@ -341,6 +341,13 @@ bool tcp_fastopen_cookie_check(struct sock *sk, u16 *mss,
cookie->len = -1;
return false;
}
+
+ /* Firewall blackhole issue check */
+ if (tcp_fastopen_active_should_disable(sk)) {
+ cookie->len = -1;
+ return false;
+ }
+
if (sysctl_tcp_fastopen & TFO_CLIENT_NO_COOKIE) {
cookie->len = -1;
return true;
@@ -380,3 +387,97 @@ bool tcp_fastopen_defer_connect(struct sock *sk, int *err)
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
+ * 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.
+ */
+
+/* Default to 1hr */
+unsigned int sysctl_tcp_fastopen_blackhole_timeout __read_mostly = 60 * 60;
+static atomic_t tfo_active_disable_times __read_mostly = ATOMIC_INIT(0);
+static unsigned long tfo_active_disable_stamp __read_mostly;
+
+/* Disable active TFO and record current jiffies and
+ * tfo_active_disable_times
+ */
+void tcp_fastopen_active_disable(void)
+{
+ atomic_inc(&tfo_active_disable_times);
+ tfo_active_disable_stamp = jiffies;
+}
+
+/* Reset tfo_active_disable_times to 0 */
+void tcp_fastopen_active_timeout_reset(void)
+{
+ atomic_set(&tfo_active_disable_times, 0);
+}
+
+/* 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)
+{
+ int tfo_da_times = atomic_read(&tfo_active_disable_times);
+ int multiplier;
+ unsigned long timeout;
+
+ if (!tfo_da_times)
+ return false;
+
+ /* Limit timout to max: 2^6 * initial timeout */
+ multiplier = 1 << min(tfo_da_times - 1, 6);
+ timeout = multiplier * sysctl_tcp_fastopen_blackhole_timeout * HZ;
+ if (time_before(jiffies, tfo_active_disable_stamp + 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 rb_node *p;
+ struct sk_buff *skb;
+ struct dst_entry *dst;
+
+ if (!tp->syn_fastopen)
+ return;
+
+ if (!tp->data_segs_in) {
+ p = rb_first(&tp->out_of_order_queue);
+ if (p && !rb_next(p)) {
+ skb = rb_entry(p, struct sk_buff, rbnode);
+ if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) {
+ tcp_fastopen_active_disable();
+ return;
+ }
+ }
+ } else if (tp->syn_fastopen_ch &&
+ atomic_read(&tfo_active_disable_times)) {
+ dst = sk_dst_get(sk);
+ if (!(dst && dst->dev && (dst->dev->flags & IFF_LOOPBACK)))
+ tcp_fastopen_active_timeout_reset();
+ dst_release(dst);
+ }
+}
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 341f021f02a2..9f342a67dc74 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5300,8 +5300,16 @@ static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
if (rst_seq_match)
tcp_reset(sk);
- else
+ else {
+ /* Disable TFO if RST is out-of-order
+ * and no data has been received
+ * for current active TFO socket
+ */
+ if (tp->syn_fastopen && !tp->data_segs_in &&
+ sk->sk_state == TCP_ESTABLISHED)
+ tcp_fastopen_active_disable();
tcp_send_challenge_ack(sk, skb);
+ }
goto discard;
}
@@ -6044,9 +6052,16 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
break;
}
- if (tp->linger2 < 0 ||
- (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
- after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt))) {
+ if (tp->linger2 < 0) {
+ tcp_done(sk);
+ NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
+ return 1;
+ }
+ if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
+ after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
+ /* Receive out of order FIN after close() */
+ if (tp->syn_fastopen && th->fin)
+ tcp_fastopen_active_disable();
tcp_done(sk);
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
return 1;
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 20cbd2f07f28..cbbafe546c0f 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1855,6 +1855,9 @@ void tcp_v4_destroy_sock(struct sock *sk)
/* Cleanup up the write buffer. */
tcp_write_queue_purge(sk);
+ /* Check if we want to disable active TFO */
+ tcp_fastopen_active_disable_ofo_check(sk);
+
/* Cleans up our, hopefully empty, out_of_order_queue. */
skb_rbtree_purge(&tp->out_of_order_queue);