net-tcp: Fast Open client - cookie-less mode
In trusted networks, e.g., intranet, data-center, the client does not
need to use Fast Open cookie to mitigate DoS attacks. In cookie-less
mode, sendmsg() with MSG_FASTOPEN flag will send SYN-data regardless
of cookie availability.
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index 03964e0..5f3ef7f 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -476,6 +476,8 @@
The values (bitmap) are:
1: Enables sending data in the opening SYN on the client
+ 5: Enables sending data in the opening SYN on the client regardless
+ of cookie availability.
Default: 0
diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 1edf96a..9febfb6 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -387,6 +387,7 @@
u8 repair_queue;
u8 do_early_retrans:1,/* Enable RFC5827 early-retransmit */
early_retrans_delayed:1, /* Delayed ER timer installed */
+ syn_data:1, /* SYN includes data */
syn_fastopen:1; /* SYN includes Fast Open option */
/* RTT measurement */
diff --git a/include/net/tcp.h b/include/net/tcp.h
index e07878d..bc7c134 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -214,6 +214,7 @@
/* Bit Flags for sysctl_tcp_fastopen */
#define TFO_CLIENT_ENABLE 1
+#define TFO_CLIENT_NO_COOKIE 4 /* Data in SYN w/o cookie option */
extern struct inet_timewait_death_row tcp_death_row;
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index c49a4fc..e67d685 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5650,7 +5650,7 @@
struct tcp_fastopen_cookie *cookie)
{
struct tcp_sock *tp = tcp_sk(sk);
- struct sk_buff *data = tcp_write_queue_head(sk);
+ struct sk_buff *data = tp->syn_data ? tcp_write_queue_head(sk) : NULL;
u16 mss = tp->rx_opt.mss_clamp;
bool syn_drop;
@@ -5665,6 +5665,9 @@
mss = opt.mss_clamp;
}
+ if (!tp->syn_fastopen) /* Ignore an unsolicited cookie */
+ cookie->len = -1;
+
/* The SYN-ACK neither has cookie nor acknowledges the data. Presumably
* the remote receives only the retransmitted (regular) SYNs: either
* the original SYN-data or the corresponding SYN-ACK is lost.
@@ -5816,7 +5819,8 @@
tcp_finish_connect(sk, skb);
- if (tp->syn_fastopen && tcp_rcv_fastopen_synack(sk, skb, &foc))
+ if ((tp->syn_fastopen || tp->syn_data) &&
+ tcp_rcv_fastopen_synack(sk, skb, &foc))
return -1;
if (sk->sk_write_pending ||
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index c5cfd5e..27a32ac 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2864,6 +2864,7 @@
struct sk_buff *syn_data = NULL, *data;
unsigned long last_syn_loss = 0;
+ tp->rx_opt.mss_clamp = tp->advmss; /* If MSS is not cached */
tcp_fastopen_cache_get(sk, &tp->rx_opt.mss_clamp, &fo->cookie,
&syn_loss, &last_syn_loss);
/* Recurring FO SYN losses: revert to regular handshake temporarily */
@@ -2873,7 +2874,9 @@
goto fallback;
}
- if (fo->cookie.len <= 0)
+ if (sysctl_tcp_fastopen & TFO_CLIENT_NO_COOKIE)
+ fo->cookie.len = -1;
+ else if (fo->cookie.len <= 0)
goto fallback;
/* MSS for SYN-data is based on cached MSS and bounded by PMTU and
@@ -2916,6 +2919,7 @@
fo->copied = data->len;
if (tcp_transmit_skb(sk, syn_data, 0, sk->sk_allocation) == 0) {
+ tp->syn_data = (fo->copied > 0);
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENACTIVE);
goto done;
}