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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>
This commit is contained in:
Eric Dumazet 2011-08-30 03:21:44 +00:00 committed by David S. Miller
parent 27e95a8c67
commit 946cedccbd
6 changed files with 40 additions and 50 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
include/linux/snmp.h
View File

@ -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
};

3
include/net/request_sock.h
View File

@ -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;

3
include/net/tcp.h
View File

@ -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);

2
net/ipv4/proc.c
View File

@ -254,6 +254,8 @@ static const struct snmp_mib snmp4_net_list[] = {
SNMP_MIB_ITEM("TCPDeferAcceptDrop", LINUX_MIB_TCPDEFERACCEPTDROP),
SNMP_MIB_ITEM("IPReversePathFilter", LINUX_MIB_IPRPFILTER),
SNMP_MIB_ITEM("TCPTimeWaitOverflow", LINUX_MIB_TCPTIMEWAITOVERFLOW),
SNMP_MIB_ITEM("TCPReqQFullDoCookies", LINUX_MIB_TCPREQQFULLDOCOOKIES),
SNMP_MIB_ITEM("TCPReqQFullDrop", LINUX_MIB_TCPREQQFULLDROP),
SNMP_MIB_SENTINEL
};

49
net/ipv4/tcp_ipv4.c
View File

@ -808,20 +808,38 @@ 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)
/*
* 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 @@ int tcp_v4_conn_request(struct sock *sk, struct sk_buff *skb)
__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 @@ 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);
#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 @@ int tcp_v4_conn_request(struct sock *sk, struct sk_buff *skb)
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) {

31
net/ipv6/tcp_ipv6.c
View File

@ -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);
@ -1179,11 +1165,7 @@ static int tcp_v6_conn_request(struct sock *sk, struct sk_buff *skb)
struct tcp_sock *tp = tcp_sk(sk);
__u32 isn = TCP_SKB_CB(skb)->when;
struct dst_entry *dst = NULL;
#ifdef CONFIG_SYN_COOKIES
int want_cookie = 0;
#else
#define want_cookie 0
#endif
if (skb->protocol == htons(ETH_P_IP))
return tcp_v4_conn_request(sk, skb);
@ -1192,14 +1174,9 @@ 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);
#ifdef CONFIG_SYN_COOKIES
if (sysctl_tcp_syncookies)
want_cookie = 1;
else
#endif
goto drop;
want_cookie = tcp_syn_flood_action(sk, skb, "TCPv6");
if (!want_cookie)
goto drop;
}
if (sk_acceptq_is_full(sk) && inet_csk_reqsk_queue_young(sk) > 1)
@ -1249,9 +1226,7 @@ static int tcp_v6_conn_request(struct sock *sk, struct sk_buff *skb)
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) {