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Subject[PATCH 1/2] xt_connlimit (kernel) - connection limiting

Adds the connlimit match that has been in POM-NG for a long time.

* works with 2.6.22, xtables'ified and all that

* will request nf_conntrack_ipv4 upon load
(otherwise it hotdrops every packet - a glitch that goes back
to at least 2.6.20.2)


Signed-off-by: Jan Engelhardt <jengelh@gmx.de>

---
include/linux/netfilter/nf_conntrack_common.h | 1
include/linux/netfilter/xt_connlimit.h | 14 +
net/ipv4/netfilter/nf_conntrack_l3proto_ipv4.c | 5
net/netfilter/Kconfig | 7
net/netfilter/Makefile | 1
net/netfilter/xt_connlimit.c | 250 +++++++++++++++++++++++++
6 files changed, 278 insertions(+)

Index: linux-2.6.22-rc3-git6/include/linux/netfilter/nf_conntrack_common.h
===================================================================
--- linux-2.6.22-rc3-git6.orig/include/linux/netfilter/nf_conntrack_common.h
+++ linux-2.6.22-rc3-git6/include/linux/netfilter/nf_conntrack_common.h
@@ -164,6 +164,7 @@ struct ip_conntrack_stat

/* call to create an explicit dependency on nf_conntrack. */
extern void need_conntrack(void);
+extern void need_conntrack_ipv4(void);

#endif /* __KERNEL__ */

Index: linux-2.6.22-rc3-git6/include/linux/netfilter/xt_connlimit.h
===================================================================
--- /dev/null
+++ linux-2.6.22-rc3-git6/include/linux/netfilter/xt_connlimit.h
@@ -0,0 +1,14 @@
+#ifndef _XT_CONNLIMIT_H
+#define _XT_CONNLIMIT_H
+
+struct xt_connlimit_data;
+
+struct xt_connlimit_info {
+ uint32_t mask;
+ unsigned int limit, inverse;
+
+ /* this needs to be at the end */
+ struct xt_connlimit_data *data;
+};
+
+#endif /* _XT_CONNLIMIT_H */
Index: linux-2.6.22-rc3-git6/net/ipv4/netfilter/nf_conntrack_l3proto_ipv4.c
===================================================================
--- linux-2.6.22-rc3-git6.orig/net/ipv4/netfilter/nf_conntrack_l3proto_ipv4.c
+++ linux-2.6.22-rc3-git6/net/ipv4/netfilter/nf_conntrack_l3proto_ipv4.c
@@ -519,3 +519,8 @@ static void __exit nf_conntrack_l3proto_

module_init(nf_conntrack_l3proto_ipv4_init);
module_exit(nf_conntrack_l3proto_ipv4_fini);
+
+void need_conntrack_ipv4(void)
+{
+}
+EXPORT_SYMBOL(need_conntrack_ipv4);
Index: linux-2.6.22-rc3-git6/net/netfilter/Kconfig
===================================================================
--- linux-2.6.22-rc3-git6.orig/net/netfilter/Kconfig
+++ linux-2.6.22-rc3-git6/net/netfilter/Kconfig
@@ -411,6 +411,13 @@ config NETFILTER_XT_MATCH_CONNBYTES
If you want to compile it as a module, say M here and read
<file:Documentation/kbuild/modules.txt>. If unsure, say `N'.

+config NETFILTER_XT_MATCH_CONNLIMIT
+ tristate '"connlimit" match support"'
+ depends on NETFILTER_XTABLES && NF_CONNTRACK_IPV4
+ ---help---
+ This match allows you to match against the number of parallel TCP
+ connections to a server per client IP address (or address block).
+
config NETFILTER_XT_MATCH_CONNMARK
tristate '"connmark" connection mark match support'
depends on NETFILTER_XTABLES
Index: linux-2.6.22-rc3-git6/net/netfilter/Makefile
===================================================================
--- linux-2.6.22-rc3-git6.orig/net/netfilter/Makefile
+++ linux-2.6.22-rc3-git6/net/netfilter/Makefile
@@ -51,6 +51,7 @@ obj-$(CONFIG_NETFILTER_XT_TARGET_CONNSEC
# matches
obj-$(CONFIG_NETFILTER_XT_MATCH_COMMENT) += xt_comment.o
obj-$(CONFIG_NETFILTER_XT_MATCH_CONNBYTES) += xt_connbytes.o
+obj-$(CONFIG_NETFILTER_XT_MATCH_CONNLIMIT) += xt_connlimit.o
obj-$(CONFIG_NETFILTER_XT_MATCH_CONNMARK) += xt_connmark.o
obj-$(CONFIG_NETFILTER_XT_MATCH_CONNTRACK) += xt_conntrack.o
obj-$(CONFIG_NETFILTER_XT_MATCH_DCCP) += xt_dccp.o
Index: linux-2.6.22-rc3-git6/net/netfilter/xt_connlimit.c
===================================================================
--- /dev/null
+++ linux-2.6.22-rc3-git6/net/netfilter/xt_connlimit.c
@@ -0,0 +1,250 @@
+/*
+ * netfilter module to limit the number of parallel tcp
+ * connections per IP address.
+ * (c) 2000 Gerd Knorr <kraxel@bytesex.org>
+ * Nov 2002: Martin Bene <martin.bene@icomedias.com>:
+ * only ignore TIME_WAIT or gone connections
+ * © Jan Engelhardt <jengelh@gmx.de>, 2007
+ *
+ * based on ...
+ *
+ * Kernel module to match connection tracking information.
+ * GPL (C) 1999 Rusty Russell (rusty@rustcorp.com.au).
+ */
+#include <linux/in.h>
+#include <linux/ip.h>
+#include <linux/list.h>
+#include <linux/module.h>
+#include <linux/skbuff.h>
+#include <linux/spinlock.h>
+#include <linux/netfilter/nf_conntrack_common.h>
+#include <linux/netfilter/nf_conntrack_tcp.h>
+#include <linux/netfilter/x_tables.h>
+#include <linux/netfilter/xt_connlimit.h>
+#include <net/netfilter/nf_conntrack.h>
+#include <net/netfilter/nf_conntrack_core.h>
+#include <net/netfilter/nf_conntrack_tuple.h>
+
+#define DEBUG 0
+
+/* we will save the tuples of all connections we care about */
+struct xt_connlimit_conn {
+ struct list_head list;
+ struct nf_conntrack_tuple tuple;
+};
+
+struct xt_connlimit_data {
+ struct list_head iphash[256];
+ spinlock_t lock;
+};
+
+static inline unsigned int connlimit_iphash(uint32_t addr)
+{
+ return (addr ^ (addr >> 8) ^ (addr >> 16) ^ (addr >> 24)) & 0xff;
+}
+
+static int count_them(struct xt_connlimit_data *data, uint32_t addr,
+ uint32_t mask, struct nf_conn *ct)
+{
+#if DEBUG
+ static const char const *tcp_state[] = {
+ "none", "established", "syn_sent", "syn_recv", "fin_wait",
+ "time_wait", "close", "close_wait", "last_ack", "listen"
+ };
+#endif
+ struct nf_conntrack_tuple_hash *found;
+ struct nf_conntrack_tuple tuple;
+ struct xt_connlimit_conn *conn;
+ struct list_head *hash, *lh;
+ int addit = 1, matches = 0;
+ struct nf_conn *found_ct;
+
+ spin_lock_bh(&data->lock);
+ tuple = ct->tuplehash[0].tuple;
+ hash = &data->iphash[connlimit_iphash(addr & mask)];
+
+ /* check the saved connections */
+ for (lh = hash->next; lh != hash; lh = lh->next) {
+ conn = list_entry(lh, struct xt_connlimit_conn, list);
+ found = nf_conntrack_find_get(&conn->tuple, ct);
+ found_ct = NULL;
+
+ if (found != NULL &&
+ (found_ct = nf_ct_tuplehash_to_ctrack(found)) != NULL &&
+ memcmp(&conn->tuple, &tuple, sizeof(tuple)) == 0 &&
+ found_ct->proto.tcp.state != TCP_CONNTRACK_TIME_WAIT)
+ /*
+ * Just to be sure we have it only once in the list.
+ * We should not see tuples twice unless someone hooks
+ * this into a table without "-p tcp --syn".
+ */
+ addit = 0;
+
+#if DEBUG
+ printk(KERN_WARNING "xt_connlimit [%u]: src=%u.%u.%u.%u:%u "
+ "dst=%u.%u.%u.%u:%d %s\n",
+ connlimit_iphash(addr & mask),
+ NIPQUAD(conn->tuple.src.u3.ip),
+ ntohs(conn->tuple.src.u.tcp.port),
+ NIPQUAD(conn->tuple.dst.u3.ip),
+ ntohs(conn->tuple.dst.u.tcp.port),
+ (found == NULL) ? "gone" :
+ tcp_state[found_ct->proto.tcp.state]);
+#endif
+
+ if (found == NULL) {
+ /* this one is gone */
+ lh = lh->prev;
+ list_del(lh->next);
+ kfree(conn);
+ continue;
+ }
+
+ if (found_ct->proto.tcp.state == TCP_CONNTRACK_TIME_WAIT) {
+ /*
+ * we do not care about connections which are
+ * closed already -> ditch it
+ */
+ lh = lh->prev;
+ list_del(lh->next);
+ kfree(conn);
+ nf_conntrack_put(&found_ct->ct_general);
+ continue;
+ }
+
+ if ((addr & mask) == (conn->tuple.src.u3.ip & mask))
+ /* same source IP address -> be counted! */
+ ++matches;
+
+ nf_conntrack_put(&found_ct->ct_general);
+ }
+
+ if (addit) {
+ /* save the new connection in our list */
+#if DEBUG
+ printk(KERN_WARNING "xt_connlimit [%u]: src=%u.%u.%u.%u:%u "
+ "dst=%u.%u.%u.%u:%u new\n",
+ connlimit_iphash(addr & mask),
+ NIPQUAD(tuple.src.u3.ip), ntohs(tuple.src.u.tcp.port),
+ NIPQUAD(tuple.dst.u3.ip), ntohs(tuple.dst.u.tcp.port));
+#endif
+
+ conn = kzalloc(sizeof(*conn), GFP_ATOMIC);
+ if (conn == NULL)
+ return -ENOMEM;
+
+ INIT_LIST_HEAD(&conn->list);
+ conn->tuple = tuple;
+ list_add(&conn->list, hash);
+ ++matches;
+ }
+
+ spin_unlock_bh(&data->lock);
+ return matches;
+}
+
+static int xt_connlimit_match(const struct sk_buff *skb,
+ const struct net_device *in,
+ const struct net_device *out,
+ const struct xt_match *match,
+ const void *matchinfo, int offset,
+ unsigned int protoff, int *hotdrop)
+{
+ const struct xt_connlimit_info *info = matchinfo;
+ enum ip_conntrack_info ctinfo;
+ const struct iphdr *iph;
+ int connections, rv;
+ struct nf_conn *ct;
+
+ ct = nf_ct_get(skb, &ctinfo);
+ if (ct == NULL) {
+ printk(KERN_INFO "xt_connlimit: INVALID connection or "
+ "nf_conntrack_ipv4 not loaded\n");
+ *hotdrop = 1;
+ return false;
+ }
+
+ iph = ip_hdr(skb);
+ connections = count_them(info->data, iph->saddr, info->mask, ct);
+ if (connections < 0) {
+ /* kmalloc failed, drop it entirely */
+ printk(KERN_DEBUG "xt_connlimit: kmalloc failed\n");
+ *hotdrop = 1;
+ return false;
+ }
+
+ rv = info->inverse ^ (connections > info->limit);
+#if DEBUG
+ printk(KERN_DEBUG "xt_connlimit: src=%u.%u.%u.%u mask=%u.%u.%u.%u "
+ "connections=%d limit=%u match=%s\n",
+ NIPQUAD(iph->saddr), NIPQUAD(info->mask),
+ connections, info->limit, match ? "yes" : "no");
+#endif
+
+ return rv;
+}
+
+static int xt_connlimit_check(const char *tablename, const void *ip,
+ const struct xt_match *match, void *matchinfo,
+ unsigned int hook_mask)
+{
+ struct xt_connlimit_info *info = matchinfo;
+ unsigned int i;
+
+ /* init private data */
+ info->data = kmalloc(sizeof(struct xt_connlimit_data), GFP_KERNEL);
+ spin_lock_init(&info->data->lock);
+ for (i = 0; i < 256; ++i)
+ INIT_LIST_HEAD(&info->data->iphash[i]);
+
+ return 1;
+}
+
+static void xt_connlimit_destroy(const struct xt_match *match, void *matchinfo)
+{
+ struct xt_connlimit_info *info = matchinfo;
+ struct xt_connlimit_conn *conn;
+ struct list_head *hash;
+ unsigned int i;
+
+ for (i = 0; i < 256; ++i) {
+ hash = &info->data->iphash[i];
+ while (hash != hash->next) {
+ conn = list_entry(hash->next,
+ struct xt_connlimit_conn, list);
+ list_del(hash->next);
+ kfree(conn);
+ }
+ }
+
+ kfree(info->data);
+ return;
+}
+
+static struct xt_match xt_connlimit_reg = {
+ .name = "connlimit",
+ .family = AF_INET,
+ .proto = IPPROTO_TCP,
+ .checkentry = xt_connlimit_check,
+ .match = xt_connlimit_match,
+ .matchsize = sizeof(struct xt_connlimit_info),
+ .destroy = xt_connlimit_destroy,
+ .me = THIS_MODULE,
+};
+
+static int __init xt_connlimit_init(void)
+{
+ need_conntrack_ipv4();
+ return xt_register_match(&xt_connlimit_reg);
+}
+
+static void __exit xt_connlimit_exit(void)
+{
+ xt_unregister_match(&xt_connlimit_reg);
+ return;
+}
+
+module_init(xt_connlimit_init);
+module_exit(xt_connlimit_exit);
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("ipt_connlimit");
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