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>

1 files changed, 2 insertions, 0 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
 };