net/netfilter/nf_nat_masquerade.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0

 #include <linux/types.h>
 #include <linux/atomic.h>
 #include <linux/inetdevice.h>
 #include <linux/netfilter.h>
 #include <linux/netfilter_ipv4.h>
 #include <linux/netfilter_ipv6.h>

 #include <net/netfilter/nf_nat_masquerade.h>

 struct masq_dev_work {
 	struct work_struct work;
 	struct net *net;
 	netns_tracker ns_tracker;
 	union nf_inet_addr addr;
 	int ifindex;
 	int (*iter)(struct nf_conn *i, void *data);
 };

 #define MAX_MASQ_WORKER_COUNT	16

 static DEFINE_MUTEX(masq_mutex);
 static unsigned int masq_refcnt __read_mostly;
 static atomic_t masq_worker_count __read_mostly;

 unsigned int
 nf_nat_masquerade_ipv4(struct sk_buff *skb, unsigned int hooknum,
 		       const struct nf_nat_range2 *range,
 		       const struct net_device *out)
 {
 	struct nf_conn *ct;
 	struct nf_conn_nat *nat;
 	enum ip_conntrack_info ctinfo;
 	struct nf_nat_range2 newrange;
 	const struct rtable *rt;
 	__be32 newsrc, nh;

 	WARN_ON(hooknum != NF_INET_POST_ROUTING);

 	ct = nf_ct_get(skb, &ctinfo);

 	WARN_ON(!(ct && (ctinfo == IP_CT_NEW || ctinfo == IP_CT_RELATED ||
 			 ctinfo == IP_CT_RELATED_REPLY)));

 	/* Source address is 0.0.0.0 - locally generated packet that is
 	 * probably not supposed to be masqueraded.
 	 */
 	if (ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.u3.ip == 0)
 		return NF_ACCEPT;

 	rt = skb_rtable(skb);
 	nh = rt_nexthop(rt, ip_hdr(skb)->daddr);
 	newsrc = inet_select_addr(out, nh, RT_SCOPE_UNIVERSE);
 	if (!newsrc) {
 		pr_info("%s ate my IP address\n", out->name);
 		return NF_DROP;
 	}

 	nat = nf_ct_nat_ext_add(ct);
 	if (nat)
 		nat->masq_index = out->ifindex;

 	/* Transfer from original range. */
 	memset(&newrange.min_addr, 0, sizeof(newrange.min_addr));
 	memset(&newrange.max_addr, 0, sizeof(newrange.max_addr));
 	newrange.flags       = range->flags | NF_NAT_RANGE_MAP_IPS;
 	newrange.min_addr.ip = newsrc;
 	newrange.max_addr.ip = newsrc;
 	newrange.min_proto   = range->min_proto;
 	newrange.max_proto   = range->max_proto;

 	/* Hand modified range to generic setup. */
 	return nf_nat_setup_info(ct, &newrange, NF_NAT_MANIP_SRC);
 }
 EXPORT_SYMBOL_GPL(nf_nat_masquerade_ipv4);

 static void iterate_cleanup_work(struct work_struct *work)
 {
 	struct nf_ct_iter_data iter_data = {};
 	struct masq_dev_work *w;

 	w = container_of(work, struct masq_dev_work, work);

 	iter_data.net = w->net;
 	iter_data.data = (void *)w;
 	nf_ct_iterate_cleanup_net(w->iter, &iter_data);

 	put_net_track(w->net, &w->ns_tracker);
 	kfree(w);
 	atomic_dec(&masq_worker_count);
 	module_put(THIS_MODULE);
 }

 /* Iterate conntrack table in the background and remove conntrack entries
  * that use the device/address being removed.
  *
  * In case too many work items have been queued already or memory allocation
  * fails iteration is skipped, conntrack entries will time out eventually.
  */
 static void nf_nat_masq_schedule(struct net *net, union nf_inet_addr *addr,
 				 int ifindex,
 				 int (*iter)(struct nf_conn *i, void *data),
 				 gfp_t gfp_flags)
 {
 	struct masq_dev_work *w;

 	if (atomic_read(&masq_worker_count) > MAX_MASQ_WORKER_COUNT)
 		return;

 	net = maybe_get_net(net);
 	if (!net)
 		return;

 	if (!try_module_get(THIS_MODULE))
 		goto err_module;

 	w = kzalloc(sizeof(*w), gfp_flags);
 	if (w) {
 		/* We can overshoot MAX_MASQ_WORKER_COUNT, no big deal */
 		atomic_inc(&masq_worker_count);

 		INIT_WORK(&w->work, iterate_cleanup_work);
 		w->ifindex = ifindex;
 		w->net = net;
 		netns_tracker_alloc(net, &w->ns_tracker, gfp_flags);
 		w->iter = iter;
 		if (addr)
 			w->addr = *addr;
 		schedule_work(&w->work);
 		return;
 	}

 	module_put(THIS_MODULE);
  err_module:
 	put_net(net);
 }

 static int device_cmp(struct nf_conn *i, void *arg)
 {
 	const struct nf_conn_nat *nat = nfct_nat(i);
 	const struct masq_dev_work *w = arg;

 	if (!nat)
 		return 0;
 	return nat->masq_index == w->ifindex;
 }

 static int masq_device_event(struct notifier_block *this,
 			     unsigned long event,
 			     void *ptr)
 {
 	const struct net_device *dev = netdev_notifier_info_to_dev(ptr);
 	struct net *net = dev_net(dev);

 	if (event == NETDEV_DOWN) {
 		/* Device was downed.  Search entire table for
 		 * conntracks which were associated with that device,
 		 * and forget them.
 		 */

 		nf_nat_masq_schedule(net, NULL, dev->ifindex,
 				     device_cmp, GFP_KERNEL);
 	}

 	return NOTIFY_DONE;
 }

 static int inet_cmp(struct nf_conn *ct, void *ptr)
 {
 	struct nf_conntrack_tuple *tuple;
 	struct masq_dev_work *w = ptr;

 	if (!device_cmp(ct, ptr))
 		return 0;

 	tuple = &ct->tuplehash[IP_CT_DIR_REPLY].tuple;

 	return nf_inet_addr_cmp(&w->addr, &tuple->dst.u3);
 }

 static int masq_inet_event(struct notifier_block *this,
 			   unsigned long event,
 			   void *ptr)
 {
 	const struct in_ifaddr *ifa = ptr;
 	const struct in_device *idev;
 	const struct net_device *dev;
 	union nf_inet_addr addr;

 	if (event != NETDEV_DOWN)
 		return NOTIFY_DONE;

 	/* The masq_dev_notifier will catch the case of the device going
 	 * down.  So if the inetdev is dead and being destroyed we have
 	 * no work to do.  Otherwise this is an individual address removal
 	 * and we have to perform the flush.
 	 */
 	idev = ifa->ifa_dev;
 	if (idev->dead)
 		return NOTIFY_DONE;

 	memset(&addr, 0, sizeof(addr));

 	addr.ip = ifa->ifa_address;

 	dev = idev->dev;
 	nf_nat_masq_schedule(dev_net(idev->dev), &addr, dev->ifindex,
 			     inet_cmp, GFP_KERNEL);

 	return NOTIFY_DONE;
 }

 static struct notifier_block masq_dev_notifier = {
 	.notifier_call	= masq_device_event,
 };

 static struct notifier_block masq_inet_notifier = {
 	.notifier_call	= masq_inet_event,
 };

 #if IS_ENABLED(CONFIG_IPV6)
 static int
 nat_ipv6_dev_get_saddr(struct net *net, const struct net_device *dev,
 		       const struct in6_addr *daddr, unsigned int srcprefs,
 		       struct in6_addr *saddr)
 {
 #ifdef CONFIG_IPV6_MODULE
 	const struct nf_ipv6_ops *v6_ops = nf_get_ipv6_ops();

 	if (!v6_ops)
 		return -EHOSTUNREACH;

 	return v6_ops->dev_get_saddr(net, dev, daddr, srcprefs, saddr);
 #else
 	return ipv6_dev_get_saddr(net, dev, daddr, srcprefs, saddr);
 #endif
 }

 unsigned int
 nf_nat_masquerade_ipv6(struct sk_buff *skb, const struct nf_nat_range2 *range,
 		       const struct net_device *out)
 {
 	enum ip_conntrack_info ctinfo;
 	struct nf_conn_nat *nat;
 	struct in6_addr src;
 	struct nf_conn *ct;
 	struct nf_nat_range2 newrange;

 	ct = nf_ct_get(skb, &ctinfo);
 	WARN_ON(!(ct && (ctinfo == IP_CT_NEW || ctinfo == IP_CT_RELATED ||
 			 ctinfo == IP_CT_RELATED_REPLY)));

 	if (nat_ipv6_dev_get_saddr(nf_ct_net(ct), out,
 				   &ipv6_hdr(skb)->daddr, 0, &src) < 0)
 		return NF_DROP;

 	nat = nf_ct_nat_ext_add(ct);
 	if (nat)
 		nat->masq_index = out->ifindex;

 	newrange.flags		= range->flags | NF_NAT_RANGE_MAP_IPS;
 	newrange.min_addr.in6	= src;
 	newrange.max_addr.in6	= src;
 	newrange.min_proto	= range->min_proto;
 	newrange.max_proto	= range->max_proto;

 	return nf_nat_setup_info(ct, &newrange, NF_NAT_MANIP_SRC);
 }
 EXPORT_SYMBOL_GPL(nf_nat_masquerade_ipv6);

 /* atomic notifier; can't call nf_ct_iterate_cleanup_net (it can sleep).
  *
  * Defer it to the system workqueue.
  *
  * As we can have 'a lot' of inet_events (depending on amount of ipv6
  * addresses being deleted), we also need to limit work item queue.
  */
 static int masq_inet6_event(struct notifier_block *this,
 			    unsigned long event, void *ptr)
 {
 	struct inet6_ifaddr *ifa = ptr;
 	const struct net_device *dev;
 	union nf_inet_addr addr;

 	if (event != NETDEV_DOWN)
 		return NOTIFY_DONE;

 	dev = ifa->idev->dev;

 	memset(&addr, 0, sizeof(addr));

 	addr.in6 = ifa->addr;

 	nf_nat_masq_schedule(dev_net(dev), &addr, dev->ifindex, inet_cmp,
 			     GFP_ATOMIC);
 	return NOTIFY_DONE;
 }

 static struct notifier_block masq_inet6_notifier = {
 	.notifier_call	= masq_inet6_event,
 };

 static int nf_nat_masquerade_ipv6_register_notifier(void)
 {
 	return register_inet6addr_notifier(&masq_inet6_notifier);
 }
 #else
 static inline int nf_nat_masquerade_ipv6_register_notifier(void) { return 0; }
 #endif

 int nf_nat_masquerade_inet_register_notifiers(void)
 {
 	int ret = 0;

 	mutex_lock(&masq_mutex);
 	if (WARN_ON_ONCE(masq_refcnt == UINT_MAX)) {
 		ret = -EOVERFLOW;
 		goto out_unlock;
 	}

 	/* check if the notifier was already set */
 	if (++masq_refcnt > 1)
 		goto out_unlock;

 	/* Register for device down reports */
 	ret = register_netdevice_notifier(&masq_dev_notifier);
 	if (ret)
 		goto err_dec;
 	/* Register IP address change reports */
 	ret = register_inetaddr_notifier(&masq_inet_notifier);
 	if (ret)
 		goto err_unregister;

 	ret = nf_nat_masquerade_ipv6_register_notifier();
 	if (ret)
 		goto err_unreg_inet;

 	mutex_unlock(&masq_mutex);
 	return ret;
 err_unreg_inet:
 	unregister_inetaddr_notifier(&masq_inet_notifier);
 err_unregister:
 	unregister_netdevice_notifier(&masq_dev_notifier);
 err_dec:
 	masq_refcnt--;
 out_unlock:
 	mutex_unlock(&masq_mutex);
 	return ret;
 }
 EXPORT_SYMBOL_GPL(nf_nat_masquerade_inet_register_notifiers);

 void nf_nat_masquerade_inet_unregister_notifiers(void)
 {
 	mutex_lock(&masq_mutex);
 	/* check if the notifiers still have clients */
 	if (--masq_refcnt > 0)
 		goto out_unlock;

 	unregister_netdevice_notifier(&masq_dev_notifier);
 	unregister_inetaddr_notifier(&masq_inet_notifier);
 #if IS_ENABLED(CONFIG_IPV6)
 	unregister_inet6addr_notifier(&masq_inet6_notifier);
 #endif
 out_unlock:
 	mutex_unlock(&masq_mutex);
 }
 EXPORT_SYMBOL_GPL(nf_nat_masquerade_inet_unregister_notifiers);
	// SPDX-License-Identifier: GPL-2.0

	#include <linux/types.h>
	#include <linux/atomic.h>
	#include <linux/inetdevice.h>
	#include <linux/netfilter.h>
	#include <linux/netfilter_ipv4.h>
	#include <linux/netfilter_ipv6.h>

	#include <net/netfilter/nf_nat_masquerade.h>

	struct masq_dev_work {
	struct work_struct work;
	struct net *net;
	netns_tracker ns_tracker;
	union nf_inet_addr addr;
	int ifindex;
	int (iter)(struct nf_conn i, void *data);
	};

	#define MAX_MASQ_WORKER_COUNT 16

	static DEFINE_MUTEX(masq_mutex);
	static unsigned int masq_refcnt __read_mostly;
	static atomic_t masq_worker_count __read_mostly;

	unsigned int
	nf_nat_masquerade_ipv4(struct sk_buff *skb, unsigned int hooknum,
	const struct nf_nat_range2 *range,
	const struct net_device *out)
	{
	struct nf_conn *ct;
	struct nf_conn_nat *nat;
	enum ip_conntrack_info ctinfo;
	struct nf_nat_range2 newrange;
	const struct rtable *rt;
	__be32 newsrc, nh;

	WARN_ON(hooknum != NF_INET_POST_ROUTING);

	ct = nf_ct_get(skb, &ctinfo);

	WARN_ON(!(ct && (ctinfo == IP_CT_NEW \|\| ctinfo == IP_CT_RELATED \|\|
	ctinfo == IP_CT_RELATED_REPLY)));

	/* Source address is 0.0.0.0 - locally generated packet that is
	* probably not supposed to be masqueraded.
	*/
	if (ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.u3.ip == 0)
	return NF_ACCEPT;

	rt = skb_rtable(skb);
	nh = rt_nexthop(rt, ip_hdr(skb)->daddr);
	newsrc = inet_select_addr(out, nh, RT_SCOPE_UNIVERSE);
	if (!newsrc) {
	pr_info("%s ate my IP address\n", out->name);
	return NF_DROP;
	}

	nat = nf_ct_nat_ext_add(ct);
	if (nat)
	nat->masq_index = out->ifindex;

	/* Transfer from original range. */
	memset(&newrange.min_addr, 0, sizeof(newrange.min_addr));
	memset(&newrange.max_addr, 0, sizeof(newrange.max_addr));
	newrange.flags = range->flags \| NF_NAT_RANGE_MAP_IPS;
	newrange.min_addr.ip = newsrc;
	newrange.max_addr.ip = newsrc;
	newrange.min_proto = range->min_proto;
	newrange.max_proto = range->max_proto;

	/* Hand modified range to generic setup. */
	return nf_nat_setup_info(ct, &newrange, NF_NAT_MANIP_SRC);
	}
	EXPORT_SYMBOL_GPL(nf_nat_masquerade_ipv4);

	static void iterate_cleanup_work(struct work_struct *work)
	{
	struct nf_ct_iter_data iter_data = {};
	struct masq_dev_work *w;

	w = container_of(work, struct masq_dev_work, work);

	iter_data.net = w->net;
	iter_data.data = (void *)w;
	nf_ct_iterate_cleanup_net(w->iter, &iter_data);

	put_net_track(w->net, &w->ns_tracker);
	kfree(w);
	atomic_dec(&masq_worker_count);
	module_put(THIS_MODULE);
	}

	/* Iterate conntrack table in the background and remove conntrack entries
	* that use the device/address being removed.
	*
	* In case too many work items have been queued already or memory allocation
	* fails iteration is skipped, conntrack entries will time out eventually.
	*/
	static void nf_nat_masq_schedule(struct net net, union nf_inet_addr addr,
	int ifindex,
	int (iter)(struct nf_conn i, void *data),
	gfp_t gfp_flags)
	{
	struct masq_dev_work *w;

	if (atomic_read(&masq_worker_count) > MAX_MASQ_WORKER_COUNT)
	return;

	net = maybe_get_net(net);
	if (!net)
	return;

	if (!try_module_get(THIS_MODULE))
	goto err_module;

	w = kzalloc(sizeof(*w), gfp_flags);
	if (w) {
	/* We can overshoot MAX_MASQ_WORKER_COUNT, no big deal */
	atomic_inc(&masq_worker_count);

	INIT_WORK(&w->work, iterate_cleanup_work);
	w->ifindex = ifindex;
	w->net = net;
	netns_tracker_alloc(net, &w->ns_tracker, gfp_flags);
	w->iter = iter;
	if (addr)
	w->addr = *addr;
	schedule_work(&w->work);
	return;
	}

	module_put(THIS_MODULE);
	err_module:
	put_net(net);
	}

	static int device_cmp(struct nf_conn i, void arg)
	{
	const struct nf_conn_nat *nat = nfct_nat(i);
	const struct masq_dev_work *w = arg;

	if (!nat)
	return 0;
	return nat->masq_index == w->ifindex;
	}

	static int masq_device_event(struct notifier_block *this,
	unsigned long event,
	void *ptr)
	{
	const struct net_device *dev = netdev_notifier_info_to_dev(ptr);
	struct net *net = dev_net(dev);

	if (event == NETDEV_DOWN) {
	/* Device was downed. Search entire table for
	* conntracks which were associated with that device,
	* and forget them.
	*/

	nf_nat_masq_schedule(net, NULL, dev->ifindex,
	device_cmp, GFP_KERNEL);
	}

	return NOTIFY_DONE;
	}

	static int inet_cmp(struct nf_conn ct, void ptr)
	{
	struct nf_conntrack_tuple *tuple;
	struct masq_dev_work *w = ptr;

	if (!device_cmp(ct, ptr))
	return 0;

	tuple = &ct->tuplehash[IP_CT_DIR_REPLY].tuple;

	return nf_inet_addr_cmp(&w->addr, &tuple->dst.u3);
	}

	static int masq_inet_event(struct notifier_block *this,
	unsigned long event,
	void *ptr)
	{
	const struct in_ifaddr *ifa = ptr;
	const struct in_device *idev;
	const struct net_device *dev;
	union nf_inet_addr addr;

	if (event != NETDEV_DOWN)
	return NOTIFY_DONE;

	/* The masq_dev_notifier will catch the case of the device going
	* down. So if the inetdev is dead and being destroyed we have
	* no work to do. Otherwise this is an individual address removal
	* and we have to perform the flush.
	*/
	idev = ifa->ifa_dev;
	if (idev->dead)
	return NOTIFY_DONE;

	memset(&addr, 0, sizeof(addr));

	addr.ip = ifa->ifa_address;

	dev = idev->dev;
	nf_nat_masq_schedule(dev_net(idev->dev), &addr, dev->ifindex,
	inet_cmp, GFP_KERNEL);

	return NOTIFY_DONE;
	}

	static struct notifier_block masq_dev_notifier = {
	.notifier_call = masq_device_event,
	};

	static struct notifier_block masq_inet_notifier = {
	.notifier_call = masq_inet_event,
	};

	#if IS_ENABLED(CONFIG_IPV6)
	static int
	nat_ipv6_dev_get_saddr(struct net net, const struct net_device dev,
	const struct in6_addr *daddr, unsigned int srcprefs,
	struct in6_addr *saddr)
	{
	#ifdef CONFIG_IPV6_MODULE
	const struct nf_ipv6_ops *v6_ops = nf_get_ipv6_ops();

	if (!v6_ops)
	return -EHOSTUNREACH;

	return v6_ops->dev_get_saddr(net, dev, daddr, srcprefs, saddr);
	#else
	return ipv6_dev_get_saddr(net, dev, daddr, srcprefs, saddr);
	#endif
	}

	unsigned int
	nf_nat_masquerade_ipv6(struct sk_buff skb, const struct nf_nat_range2 range,
	const struct net_device *out)
	{
	enum ip_conntrack_info ctinfo;
	struct nf_conn_nat *nat;
	struct in6_addr src;
	struct nf_conn *ct;
	struct nf_nat_range2 newrange;

	ct = nf_ct_get(skb, &ctinfo);
	WARN_ON(!(ct && (ctinfo == IP_CT_NEW \|\| ctinfo == IP_CT_RELATED \|\|
	ctinfo == IP_CT_RELATED_REPLY)));

	if (nat_ipv6_dev_get_saddr(nf_ct_net(ct), out,
	&ipv6_hdr(skb)->daddr, 0, &src) < 0)
	return NF_DROP;

	nat = nf_ct_nat_ext_add(ct);
	if (nat)
	nat->masq_index = out->ifindex;

	newrange.flags = range->flags \| NF_NAT_RANGE_MAP_IPS;
	newrange.min_addr.in6 = src;
	newrange.max_addr.in6 = src;
	newrange.min_proto = range->min_proto;
	newrange.max_proto = range->max_proto;

	return nf_nat_setup_info(ct, &newrange, NF_NAT_MANIP_SRC);
	}
	EXPORT_SYMBOL_GPL(nf_nat_masquerade_ipv6);

	/* atomic notifier; can't call nf_ct_iterate_cleanup_net (it can sleep).
	*
	* Defer it to the system workqueue.
	*
	* As we can have 'a lot' of inet_events (depending on amount of ipv6
	* addresses being deleted), we also need to limit work item queue.
	*/
	static int masq_inet6_event(struct notifier_block *this,
	unsigned long event, void *ptr)
	{
	struct inet6_ifaddr *ifa = ptr;
	const struct net_device *dev;
	union nf_inet_addr addr;

	if (event != NETDEV_DOWN)
	return NOTIFY_DONE;

	dev = ifa->idev->dev;

	memset(&addr, 0, sizeof(addr));

	addr.in6 = ifa->addr;

	nf_nat_masq_schedule(dev_net(dev), &addr, dev->ifindex, inet_cmp,
	GFP_ATOMIC);
	return NOTIFY_DONE;
	}

	static struct notifier_block masq_inet6_notifier = {
	.notifier_call = masq_inet6_event,
	};

	static int nf_nat_masquerade_ipv6_register_notifier(void)
	{
	return register_inet6addr_notifier(&masq_inet6_notifier);
	}
	#else
	static inline int nf_nat_masquerade_ipv6_register_notifier(void) { return 0; }
	#endif

	int nf_nat_masquerade_inet_register_notifiers(void)
	{
	int ret = 0;

	mutex_lock(&masq_mutex);
	if (WARN_ON_ONCE(masq_refcnt == UINT_MAX)) {
	ret = -EOVERFLOW;
	goto out_unlock;
	}

	/* check if the notifier was already set */
	if (++masq_refcnt > 1)
	goto out_unlock;

	/* Register for device down reports */
	ret = register_netdevice_notifier(&masq_dev_notifier);
	if (ret)
	goto err_dec;
	/* Register IP address change reports */
	ret = register_inetaddr_notifier(&masq_inet_notifier);
	if (ret)
	goto err_unregister;

	ret = nf_nat_masquerade_ipv6_register_notifier();
	if (ret)
	goto err_unreg_inet;

	mutex_unlock(&masq_mutex);
	return ret;
	err_unreg_inet:
	unregister_inetaddr_notifier(&masq_inet_notifier);
	err_unregister:
	unregister_netdevice_notifier(&masq_dev_notifier);
	err_dec:
	masq_refcnt--;
	out_unlock:
	mutex_unlock(&masq_mutex);
	return ret;
	}
	EXPORT_SYMBOL_GPL(nf_nat_masquerade_inet_register_notifiers);

	void nf_nat_masquerade_inet_unregister_notifiers(void)
	{
	mutex_lock(&masq_mutex);
	/* check if the notifiers still have clients */
	if (--masq_refcnt > 0)
	goto out_unlock;

	unregister_netdevice_notifier(&masq_dev_notifier);
	unregister_inetaddr_notifier(&masq_inet_notifier);
	#if IS_ENABLED(CONFIG_IPV6)
	unregister_inet6addr_notifier(&masq_inet6_notifier);
	#endif
	out_unlock:
	mutex_unlock(&masq_mutex);
	}
	EXPORT_SYMBOL_GPL(nf_nat_masquerade_inet_unregister_notifiers);