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>
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 1c12b8e..c34f015 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -808,20 +808,38 @@
kfree(inet_rsk(req)->opt);
}
-static void syn_flood_warning(const struct sk_buff *skb)
+/*
+ * Return 1 if a syncookie should be sent
+ */
+int tcp_syn_flood_action(struct sock *sk,
+ const struct sk_buff *skb,
+ const char *proto)
{
- const char *msg;
+ const char *msg = "Dropping request";
+ int want_cookie = 0;
+ struct listen_sock *lopt;
+
+
#ifdef CONFIG_SYN_COOKIES
- if (sysctl_tcp_syncookies)
+ if (sysctl_tcp_syncookies) {
msg = "Sending cookies";
- else
+ want_cookie = 1;
+ NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPREQQFULLDOCOOKIES);
+ } else
#endif
- msg = "Dropping request";
+ NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPREQQFULLDROP);
- pr_info("TCP: Possible SYN flooding on port %d. %s.\n",
- ntohs(tcp_hdr(skb)->dest), msg);
+ lopt = inet_csk(sk)->icsk_accept_queue.listen_opt;
+ if (!lopt->synflood_warned) {
+ lopt->synflood_warned = 1;
+ pr_info("%s: Possible SYN flooding on port %d. %s. "
+ " Check SNMP counters.\n",
+ proto, ntohs(tcp_hdr(skb)->dest), msg);
+ }
+ return want_cookie;
}
+EXPORT_SYMBOL(tcp_syn_flood_action);
/*
* Save and compile IPv4 options into the request_sock if needed.
@@ -1235,11 +1253,7 @@
__be32 saddr = ip_hdr(skb)->saddr;
__be32 daddr = ip_hdr(skb)->daddr;
__u32 isn = TCP_SKB_CB(skb)->when;
-#ifdef CONFIG_SYN_COOKIES
int want_cookie = 0;
-#else
-#define want_cookie 0 /* Argh, why doesn't gcc optimize this :( */
-#endif
/* Never answer to SYNs send to broadcast or multicast */
if (skb_rtable(skb)->rt_flags & (RTCF_BROADCAST | RTCF_MULTICAST))
@@ -1250,14 +1264,9 @@
* evidently real one.
*/
if (inet_csk_reqsk_queue_is_full(sk) && !isn) {
- if (net_ratelimit())
- syn_flood_warning(skb);
-#ifdef CONFIG_SYN_COOKIES
- if (sysctl_tcp_syncookies) {
- want_cookie = 1;
- } else
-#endif
- goto drop;
+ want_cookie = tcp_syn_flood_action(sk, skb, "TCP");
+ if (!want_cookie)
+ goto drop;
}
/* Accept backlog is full. If we have already queued enough
@@ -1303,9 +1312,7 @@
while (l-- > 0)
*c++ ^= *hash_location++;
-#ifdef CONFIG_SYN_COOKIES
want_cookie = 0; /* not our kind of cookie */
-#endif
tmp_ext.cookie_out_never = 0; /* false */
tmp_ext.cookie_plus = tmp_opt.cookie_plus;
} else if (!tp->rx_opt.cookie_in_always) {