netfilter: xtables: idletimer target implementation

This patch implements an idletimer Xtables target that can be used to
identify when interfaces have been idle for a certain period of time.

Timers are identified by labels and are created when a rule is set with a new
label.  The rules also take a timeout value (in seconds) as an option.  If
more than one rule uses the same timer label, the timer will be restarted
whenever any of the rules get a hit.

One entry for each timer is created in sysfs.  This attribute contains the
timer remaining for the timer to expire.  The attributes are located under
the xt_idletimer class:

/sys/class/xt_idletimer/timers/<label>

When the timer expires, the target module sends a sysfs notification to the
userspace, which can then decide what to do (eg. disconnect to save power).

Cc: Timo Teras <timo.teras@iki.fi>
Signed-off-by: Luciano Coelho <luciano.coelho@nokia.com>
Signed-off-by: Patrick McHardy <kaber@trash.net>

include/linux/netfilter/Kbuild

@@ -8,6 +8,7 @@ header-y += xt_CONNMARK.h
 header-y += xt_CONNSECMARK.h
 header-y += xt_CT.h
 header-y += xt_DSCP.h
+header-y += xt_IDLETIMER.h
 header-y += xt_LED.h
 header-y += xt_MARK.h
 header-y += xt_NFLOG.h

include/linux/netfilter/xt_IDLETIMER.h

+/*
+ * linux/include/linux/netfilter/xt_IDLETIMER.h
+ *
+ * Header file for Xtables timer target module.
+ *
+ * Copyright (C) 2004, 2010 Nokia Corporation
+ * Written by Timo Teras <ext-timo.teras@nokia.com>
+ *
+ * Converted to x_tables and forward-ported to 2.6.34
+ * by Luciano Coelho <luciano.coelho@nokia.com>
+ *
+ * Contact: Luciano Coelho <luciano.coelho@nokia.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * version 2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
+ * 02110-1301 USA
+ */
+
+#ifndef _XT_IDLETIMER_H
+#define _XT_IDLETIMER_H
+
+#include <linux/types.h>
+
+#define MAX_IDLETIMER_LABEL_SIZE 28
+
+struct idletimer_tg_info {
+	__u32 timeout;
+
+	char label[MAX_IDLETIMER_LABEL_SIZE];
+
+	/* for kernel module internal use only */
+	struct idletimer_tg *timer __attribute((aligned(8)));
+};
+
+#endif

net/netfilter/Kconfig

@@ -424,6 +424,18 @@ config NETFILTER_XT_TARGET_HL
 	since you can easily create immortal packets that loop
 	forever on the network.
 
+config NETFILTER_XT_TARGET_IDLETIMER
+	tristate  "IDLETIMER target support"
+	depends on NETFILTER_ADVANCED
+	help
+
+	  This option adds the `IDLETIMER' target.  Each matching packet
+	  resets the timer associated with label specified when the rule is
+	  added.  When the timer expires, it triggers a sysfs notification.
+	  The remaining time for expiration can be read via sysfs.
+
+	  To compile it as a module, choose M here.  If unsure, say N.
+
 config NETFILTER_XT_TARGET_LED
 	tristate '"LED" target support'
 	depends on LEDS_CLASS && LEDS_TRIGGERS

net/netfilter/Makefile

@@ -61,6 +61,7 @@ obj-$(CONFIG_NETFILTER_XT_TARGET_TCPMSS) += xt_TCPMSS.o
 obj-$(CONFIG_NETFILTER_XT_TARGET_TCPOPTSTRIP) += xt_TCPOPTSTRIP.o
 obj-$(CONFIG_NETFILTER_XT_TARGET_TEE) += xt_TEE.o
 obj-$(CONFIG_NETFILTER_XT_TARGET_TRACE) += xt_TRACE.o
+obj-$(CONFIG_NETFILTER_XT_TARGET_IDLETIMER) += xt_IDLETIMER.o
 
 # matches
 obj-$(CONFIG_NETFILTER_XT_MATCH_CLUSTER) += xt_cluster.o

net/netfilter/xt_IDLETIMER.c

+/*
+ * linux/net/netfilter/xt_IDLETIMER.c
+ *
+ * Netfilter module to trigger a timer when packet matches.
+ * After timer expires a kevent will be sent.
+ *
+ * Copyright (C) 2004, 2010 Nokia Corporation
+ * Written by Timo Teras <ext-timo.teras@nokia.com>
+ *
+ * Converted to x_tables and reworked for upstream inclusion
+ * by Luciano Coelho <luciano.coelho@nokia.com>
+ *
+ * Contact: Luciano Coelho <luciano.coelho@nokia.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * version 2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
+ * 02110-1301 USA
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/module.h>
+#include <linux/timer.h>
+#include <linux/list.h>
+#include <linux/mutex.h>
+#include <linux/netfilter.h>
+#include <linux/netfilter/x_tables.h>
+#include <linux/netfilter/xt_IDLETIMER.h>
+#include <linux/kobject.h>
+#include <linux/workqueue.h>
+#include <linux/sysfs.h>
+
+struct idletimer_tg_attr {
+	struct attribute attr;
+	ssize_t	(*show)(struct kobject *kobj,
+			struct attribute *attr, char *buf);
+};
+
+struct idletimer_tg {
+	struct list_head entry;
+	struct timer_list timer;
+	struct work_struct work;
+
+	struct kobject *kobj;
+	struct idletimer_tg_attr attr;
+
+	unsigned int refcnt;
+};
+
+static LIST_HEAD(idletimer_tg_list);
+static DEFINE_MUTEX(list_mutex);
+
+static struct kobject *idletimer_tg_kobj;
+
+static
+struct idletimer_tg *__idletimer_tg_find_by_label(const char *label)
+{
+	struct idletimer_tg *entry;
+
+	BUG_ON(!label);
+
+	list_for_each_entry(entry, &idletimer_tg_list, entry) {
+		if (!strcmp(label, entry->attr.attr.name))
+			return entry;
+	}
+
+	return NULL;
+}
+
+static ssize_t idletimer_tg_show(struct kobject *kobj, struct attribute *attr,
+				 char *buf)
+{
+	struct idletimer_tg *timer;
+	unsigned long expires = 0;
+
+	mutex_lock(&list_mutex);
+
+	timer =	__idletimer_tg_find_by_label(attr->name);
+	if (timer)
+		expires = timer->timer.expires;
+
+	mutex_unlock(&list_mutex);
+
+	if (time_after(expires, jiffies))
+		return sprintf(buf, "%u\n",
+			       jiffies_to_msecs(expires - jiffies) / 1000);
+
+	return sprintf(buf, "0\n");
+}
+
+static void idletimer_tg_work(struct work_struct *work)
+{
+	struct idletimer_tg *timer = container_of(work, struct idletimer_tg,
+						  work);
+
+	sysfs_notify(idletimer_tg_kobj, NULL, timer->attr.attr.name);
+}
+
+static void idletimer_tg_expired(unsigned long data)
+{
+	struct idletimer_tg *timer = (struct idletimer_tg *) data;
+
+	pr_debug("timer %s expired\n", timer->attr.attr.name);
+
+	schedule_work(&timer->work);
+}
+
+static int idletimer_tg_create(struct idletimer_tg_info *info)
+{
+	int ret;
+
+	info->timer = kmalloc(sizeof(*info->timer), GFP_KERNEL);
+	if (!info->timer) {
+		pr_debug("couldn't alloc timer\n");
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	info->timer->attr.attr.name = kstrdup(info->label, GFP_KERNEL);
+	if (!info->timer->attr.attr.name) {
+		pr_debug("couldn't alloc attribute name\n");
+		ret = -ENOMEM;
+		goto out_free_timer;
+	}
+	info->timer->attr.attr.mode = S_IRUGO;
+	info->timer->attr.show = idletimer_tg_show;
+
+	ret = sysfs_create_file(idletimer_tg_kobj, &info->timer->attr.attr);
+	if (ret < 0) {
+		pr_debug("couldn't add file to sysfs");
+		goto out_free_attr;
+	}
+
+	list_add(&info->timer->entry, &idletimer_tg_list);
+
+	setup_timer(&info->timer->timer, idletimer_tg_expired,
+		    (unsigned long) info->timer);
+	info->timer->refcnt = 1;
+
+	mod_timer(&info->timer->timer,
+		  msecs_to_jiffies(info->timeout * 1000) + jiffies);
+
+	INIT_WORK(&info->timer->work, idletimer_tg_work);
+
+	return 0;
+
+out_free_attr:
+	kfree(info->timer->attr.attr.name);
+out_free_timer:
+	kfree(info->timer);
+out:
+	return ret;
+}
+
+/*
+ * The actual xt_tables plugin.
+ */
+static unsigned int idletimer_tg_target(struct sk_buff *skb,
+					 const struct xt_action_param *par)
+{
+	const struct idletimer_tg_info *info = par->targinfo;
+
+	pr_debug("resetting timer %s, timeout period %u\n",
+		 info->label, info->timeout);
+
+	BUG_ON(!info->timer);
+
+	mod_timer(&info->timer->timer,
+		  msecs_to_jiffies(info->timeout * 1000) + jiffies);
+
+	return XT_CONTINUE;
+}
+
+static int idletimer_tg_checkentry(const struct xt_tgchk_param *par)
+{
+	struct idletimer_tg_info *info = par->targinfo;
+	int ret;
+
+	pr_debug("checkentry targinfo%s\n", info->label);
+
+	if (info->timeout == 0) {
+		pr_debug("timeout value is zero\n");
+		return -EINVAL;
+	}
+
+	if (info->label[0] == '\0' ||
+	    strnlen(info->label,
+		    MAX_IDLETIMER_LABEL_SIZE) == MAX_IDLETIMER_LABEL_SIZE) {
+		pr_debug("label is empty or not nul-terminated\n");
+		return -EINVAL;
+	}
+
+	mutex_lock(&list_mutex);
+
+	info->timer = __idletimer_tg_find_by_label(info->label);
+	if (info->timer) {
+		info->timer->refcnt++;
+		mod_timer(&info->timer->timer,
+			  msecs_to_jiffies(info->timeout * 1000) + jiffies);
+
+		pr_debug("increased refcnt of timer %s to %u\n",
+			 info->label, info->timer->refcnt);
+	} else {
+		ret = idletimer_tg_create(info);
+		if (ret < 0) {
+			pr_debug("failed to create timer\n");
+			mutex_unlock(&list_mutex);
+			return ret;
+		}
+	}
+
+	mutex_unlock(&list_mutex);
+	return 0;
+}
+
+static void idletimer_tg_destroy(const struct xt_tgdtor_param *par)
+{
+	const struct idletimer_tg_info *info = par->targinfo;
+
+	pr_debug("destroy targinfo %s\n", info->label);
+
+	mutex_lock(&list_mutex);
+
+	if (--info->timer->refcnt == 0) {
+		pr_debug("deleting timer %s\n", info->label);
+
+		list_del(&info->timer->entry);
+		del_timer_sync(&info->timer->timer);
+		sysfs_remove_file(idletimer_tg_kobj, &info->timer->attr.attr);
+		kfree(info->timer->attr.attr.name);
+		kfree(info->timer);
+	} else {
+		pr_debug("decreased refcnt of timer %s to %u\n",
+			 info->label, info->timer->refcnt);
+	}
+
+	mutex_unlock(&list_mutex);
+}
+
+static struct xt_target idletimer_tg __read_mostly = {
+	.name		= "IDLETIMER",
+	.family		= NFPROTO_UNSPEC,
+	.target		= idletimer_tg_target,
+	.targetsize     = sizeof(struct idletimer_tg_info),
+	.checkentry	= idletimer_tg_checkentry,
+	.destroy        = idletimer_tg_destroy,
+	.me		= THIS_MODULE,
+};
+
+static struct class *idletimer_tg_class;
+
+static struct device *idletimer_tg_device;
+
+static int __init idletimer_tg_init(void)
+{
+	int err;
+
+	idletimer_tg_class = class_create(THIS_MODULE, "xt_idletimer");
+	err = PTR_ERR(idletimer_tg_class);
+	if (IS_ERR(idletimer_tg_class)) {
+		pr_debug("couldn't register device class\n");
+		goto out;
+	}
+
+	idletimer_tg_device = device_create(idletimer_tg_class, NULL,
+					    MKDEV(0, 0), NULL, "timers");
+	err = PTR_ERR(idletimer_tg_device);
+	if (IS_ERR(idletimer_tg_device)) {
+		pr_debug("couldn't register system device\n");
+		goto out_class;
+	}
+
+	idletimer_tg_kobj = &idletimer_tg_device->kobj;
+
+	err =  xt_register_target(&idletimer_tg);
+	if (err < 0) {
+		pr_debug("couldn't register xt target\n");
+		goto out_dev;
+	}
+
+	return 0;
+out_dev:
+	device_destroy(idletimer_tg_class, MKDEV(0, 0));
+out_class:
+	class_destroy(idletimer_tg_class);
+out:
+	return err;
+}
+
+static void __exit idletimer_tg_exit(void)
+{
+	xt_unregister_target(&idletimer_tg);
+
+	device_destroy(idletimer_tg_class, MKDEV(0, 0));
+	class_destroy(idletimer_tg_class);
+}
+
+module_init(idletimer_tg_init);
+module_exit(idletimer_tg_exit);
+
+MODULE_AUTHOR("Timo Teras <ext-timo.teras@nokia.com>");
+MODULE_AUTHOR("Luciano Coelho <luciano.coelho@nokia.com>");
+MODULE_DESCRIPTION("Xtables: idle time monitor");
+MODULE_LICENSE("GPL v2");