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Date: Fri, 12 Aug 2011 08:08:30 +0200
From: Eric Dumazet <eric.dumazet@...il.com>
To: David Miller <davem@...emloft.net>
Cc: therbert@...gle.com, netdev@...r.kernel.org
Subject: [PATCH] tcp: Use LIMIT_NETDEBUG in syn_flood_warning()
Le jeudi 11 août 2011 à 08:33 +0200, Eric Dumazet a écrit :
> Le mercredi 10 août 2011 à 23:13 -0700, David Miller a écrit :
> > From: Tom Herbert <therbert@...gle.com>
> > Date: Wed, 10 Aug 2011 22:38:02 -0700 (PDT)
> >
> > > Rather than printing the message to the log, use a mib counter to keep
> > > track of the count of occurences of syn cookies being used or syn
> > > being dropped when request queue is full.
> > >
> > > Rationale is these messages can fill up /var/log/messages on server
> > > which is simply under heavy load... I'm not sure how much more useful
> > > they would be in identifying a server DOS attack (compared to
> > > counters).
> > >
> > > Signed-off-by: Tom Herbert <therbert@...gle.com>
> >
> > Print the message once, and also do the counters.
> >
> > Say something like "Possible SYN flooding, see SNMP counters." or
> > similar.
> >
> > Because if people are grepping for that message in their logs, they
> > will now have a false sense of confidence seeing it not being there
> > any more.
>
> An alternative would be to guard the message by net_msg_warn
> (/proc/sys/net/core/warnings)
>
> LIMIT_NETDEBUG(KERN_INFO "TCP: Possible SYN flooding on port %d. %s.\n"
> ...)
Here is a patch implementing this.
We could add mib counters later in a second patch, inside
tcp_syn_flood_warning()
Thanks
[PATCH] tcp: Use LIMIT_NETDEBUG in syn_flood_warning()
LIMIT_NETDEBUG allows the admin to disable some warning messages :
echo 0 > /proc/sys/net/core/warnings
Use it to avoid filling syslog on busy servers.
Based on a previous patch from Tom Herbert
Factorize syn_flood_warning() IPv4/IPv6 implementations
Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
CC: Tom Herbert <therbert@...gle.com>
---
include/net/tcp.h | 1 +
net/ipv4/tcp_ipv4.c | 14 ++++++--------
net/ipv6/tcp_ipv6.c | 17 +----------------
3 files changed, 8 insertions(+), 24 deletions(-)
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 149a415..964341c 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -460,6 +460,7 @@ 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 void tcp_syn_flood_warning(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);
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 1c12b8e..9e622da 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -808,20 +808,19 @@ static void tcp_v4_reqsk_destructor(struct request_sock *req)
kfree(inet_rsk(req)->opt);
}
-static void syn_flood_warning(const struct sk_buff *skb)
+void tcp_syn_flood_warning(const struct sk_buff *skb, const char *proto)
{
- const char *msg;
+ const char *msg = "Dropping request";
#ifdef CONFIG_SYN_COOKIES
if (sysctl_tcp_syncookies)
msg = "Sending cookies";
- else
#endif
- msg = "Dropping request";
- pr_info("TCP: Possible SYN flooding on port %d. %s.\n",
- ntohs(tcp_hdr(skb)->dest), msg);
+ LIMIT_NETDEBUG(KERN_INFO "%s: Possible SYN flooding on port %d. %s.\n",
+ proto, ntohs(tcp_hdr(skb)->dest), msg);
}
+EXPORT_SYMBOL(tcp_syn_flood_warning);
/*
* Save and compile IPv4 options into the request_sock if needed.
@@ -1250,8 +1249,7 @@ int tcp_v4_conn_request(struct sock *sk, struct sk_buff *skb)
* evidently real one.
*/
if (inet_csk_reqsk_queue_is_full(sk) && !isn) {
- if (net_ratelimit())
- syn_flood_warning(skb);
+ tcp_syn_flood_warning(skb, "TCP");
#ifdef CONFIG_SYN_COOKIES
if (sysctl_tcp_syncookies) {
want_cookie = 1;
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index d1fb63f..a043386 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -531,20 +531,6 @@ static int tcp_v6_rtx_synack(struct sock *sk, struct request_sock *req,
return tcp_v6_send_synack(sk, req, rvp);
}
-static inline void syn_flood_warning(struct sk_buff *skb)
-{
-#ifdef CONFIG_SYN_COOKIES
- if (sysctl_tcp_syncookies)
- printk(KERN_INFO
- "TCPv6: Possible SYN flooding on port %d. "
- "Sending cookies.\n", ntohs(tcp_hdr(skb)->dest));
- else
-#endif
- printk(KERN_INFO
- "TCPv6: Possible SYN flooding on port %d. "
- "Dropping request.\n", ntohs(tcp_hdr(skb)->dest));
-}
-
static void tcp_v6_reqsk_destructor(struct request_sock *req)
{
kfree_skb(inet6_rsk(req)->pktopts);
@@ -1192,8 +1178,7 @@ static int tcp_v6_conn_request(struct sock *sk, struct sk_buff *skb)
goto drop;
if (inet_csk_reqsk_queue_is_full(sk) && !isn) {
- if (net_ratelimit())
- syn_flood_warning(skb);
+ tcp_syn_flood_warning(skb, "TCPv6");
#ifdef CONFIG_SYN_COOKIES
if (sysctl_tcp_syncookies)
want_cookie = 1;
--
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