tcp: Change possible SYN flooding messages

"Possible SYN flooding on port xxxx " messages can fill logs on servers.

Change logic to log the message only once per listener, and add two new
SNMP counters to track :

TCPReqQFullDoCookies : number of times a SYNCOOKIE was replied to client

TCPReqQFullDrop : number of times a SYN request was dropped because
syncookies were not enabled.

Based on a prior patch from Tom Herbert, and suggestions from David.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
CC: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 7 insertions, 1 deletions

diff --git a/include/linux/snmp.h b/include/linux/snmp.h
index 12b2b18e50c1..e16557a357e5 100644
--- a/include/linux/snmp.h
+++ b/include/linux/snmp.h
@@ -231,6 +231,8 @@ enum
         LINUX_MIB_TCPDEFERACCEPTDROP,
         LINUX_MIB_IPRPFILTER, /* IP Reverse Path Filter (rp_filter) */
         LINUX_MIB_TCPTIMEWAITOVERFLOW,          /* TCPTimeWaitOverflow */
+        LINUX_MIB_TCPREQQFULLDOCOOKIES,         /* TCPReqQFullDoCookies */
+        LINUX_MIB_TCPREQQFULLDROP,              /* TCPReqQFullDrop */
         __LINUX_MIB_MAX
 };
 
diff --git a/include/net/request_sock.h b/include/net/request_sock.h
index 99e6e19b57c2..4c0766e201e3 100644
--- a/include/net/request_sock.h
+++ b/include/net/request_sock.h
@@ -96,7 +96,8 @@ extern int sysctl_max_syn_backlog;
  */
 struct listen_sock {
         u8                      max_qlen_log;
-        /* 3 bytes hole, try to use */
+        u8                      synflood_warned;
+        /* 2 bytes hole, try to use */
         int                     qlen;
         int                     qlen_young;
         int                     clock_hand;
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 149a415d1e0a..e9b48b094683 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -460,6 +460,9 @@ extern int tcp_write_wakeup(struct sock *);
 extern void tcp_send_fin(struct sock *sk);
 extern void tcp_send_active_reset(struct sock *sk, gfp_t priority);
 extern int tcp_send_synack(struct sock *);
+extern int tcp_syn_flood_action(struct sock *sk,
+                                const struct sk_buff *skb,
+                                const char *proto);
 extern void tcp_push_one(struct sock *, unsigned int mss_now);
 extern void tcp_send_ack(struct sock *sk);
 extern void tcp_send_delayed_ack(struct sock *sk);