netfilter: nat: merge ipv4 and ipv6 masquerade functionality

Before:
   text	   data	    bss	    dec	    hex	filename
  13916	   1412	   4128	  19456	   4c00	nf_nat.ko
   4510	    968	      4	   5482	   156a	nf_nat_ipv4.ko
   5146	    944	      8	   6098	   17d2	nf_nat_ipv6.ko

After:
   text	   data	    bss	    dec	    hex	filename
  16566	   1576	   4136	  22278	   5706	nf_nat.ko
   3187	    844	      0	   4031	    fbf	nf_nat_ipv4.ko
   3598	    844	      0	   4442	   115a	nf_nat_ipv6.ko

... so no drastic changes in combined size.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

3 files changed, 366 insertions, 0 deletions

diff --git a/net/netfilter/Kconfig b/net/netfilter/Kconfig
index fefd63a243f2..5a753cec005b 100644
--- a/net/netfilter/Kconfig
+++ b/net/netfilter/Kconfig
@@ -431,6 +431,9 @@ config NF_NAT_TFTP
 config NF_NAT_REDIRECT
 	bool
 
+config NF_NAT_MASQUERADE
+	bool
+
 config NETFILTER_SYNPROXY
 	tristate
 
diff --git a/net/netfilter/Makefile b/net/netfilter/Makefile
index e66067befa42..c7910706f8dd 100644
--- a/net/netfilter/Makefile
+++ b/net/netfilter/Makefile
@@ -56,6 +56,7 @@ obj-$(CONFIG_NF_LOG_NETDEV) += nf_log_netdev.o
 
 obj-$(CONFIG_NF_NAT) += nf_nat.o
 nf_nat-$(CONFIG_NF_NAT_REDIRECT) += nf_nat_redirect.o
+nf_nat-$(CONFIG_NF_NAT_MASQUERADE) += nf_nat_masquerade.o
 
 # NAT helpers
 obj-$(CONFIG_NF_NAT_AMANDA) += nf_nat_amanda.o
diff --git a/net/netfilter/nf_nat_masquerade.c b/net/netfilter/nf_nat_masquerade.c
new file mode 100644
index 000000000000..86fa4dcc63c5
--- /dev/null
+++ b/net/netfilter/nf_nat_masquerade.c
@@ -0,0 +1,362 @@
+// 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/ipv4/nf_nat_masquerade.h>
+#include <net/netfilter/ipv6/nf_nat_masquerade.h>
+
+static DEFINE_MUTEX(masq_mutex);
+static unsigned int masq_refcnt __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 int device_cmp(struct nf_conn *i, void *ifindex)
+{
+	const struct nf_conn_nat *nat = nfct_nat(i);
+
+	if (!nat)
+		return 0;
+	return nat->masq_index == (int)(long)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_ct_iterate_cleanup_net(net, device_cmp,
+					  (void *)(long)dev->ifindex, 0, 0);
+	}
+
+	return NOTIFY_DONE;
+}
+
+static int inet_cmp(struct nf_conn *ct, void *ptr)
+{
+	struct in_ifaddr *ifa = (struct in_ifaddr *)ptr;
+	struct net_device *dev = ifa->ifa_dev->dev;
+	struct nf_conntrack_tuple *tuple;
+
+	if (!device_cmp(ct, (void *)(long)dev->ifindex))
+		return 0;
+
+	tuple = &ct->tuplehash[IP_CT_DIR_REPLY].tuple;
+
+	return ifa->ifa_address == tuple->dst.u3.ip;
+}
+
+static int masq_inet_event(struct notifier_block *this,
+			   unsigned long event,
+			   void *ptr)
+{
+	struct in_device *idev = ((struct in_ifaddr *)ptr)->ifa_dev;
+	struct net *net = dev_net(idev->dev);
+
+	/* 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.
+	 */
+	if (idev->dead)
+		return NOTIFY_DONE;
+
+	if (event == NETDEV_DOWN)
+		nf_ct_iterate_cleanup_net(net, inet_cmp, ptr, 0, 0);
+
+	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,
+};
+
+int nf_nat_masquerade_ipv4_register_notifier(void)
+{
+	int ret = 0;
+
+	mutex_lock(&masq_mutex);
+	/* 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;
+
+	mutex_unlock(&masq_mutex);
+	return ret;
+
+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_ipv4_register_notifier);
+
+void nf_nat_masquerade_ipv4_unregister_notifier(void)
+{
+	mutex_lock(&masq_mutex);
+	/* check if the notifier still has clients */
+	if (--masq_refcnt > 0)
+		goto out_unlock;
+
+	unregister_netdevice_notifier(&masq_dev_notifier);
+	unregister_inetaddr_notifier(&masq_inet_notifier);
+out_unlock:
+	mutex_unlock(&masq_mutex);
+}
+EXPORT_SYMBOL_GPL(nf_nat_masquerade_ipv4_unregister_notifier);
+
+#if IS_ENABLED(CONFIG_IPV6)
+static atomic_t v6_worker_count __read_mostly;
+
+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);
+
+struct masq_dev_work {
+	struct work_struct work;
+	struct net *net;
+	struct in6_addr addr;
+	int ifindex;
+};
+
+static int inet6_cmp(struct nf_conn *ct, void *work)
+{
+	struct masq_dev_work *w = (struct masq_dev_work *)work;
+	struct nf_conntrack_tuple *tuple;
+
+	if (!device_cmp(ct, (void *)(long)w->ifindex))
+		return 0;
+
+	tuple = &ct->tuplehash[IP_CT_DIR_REPLY].tuple;
+
+	return ipv6_addr_equal(&w->addr, &tuple->dst.u3.in6);
+}
+
+static void iterate_cleanup_work(struct work_struct *work)
+{
+	struct masq_dev_work *w;
+
+	w = container_of(work, struct masq_dev_work, work);
+
+	nf_ct_iterate_cleanup_net(w->net, inet6_cmp, (void *)w, 0, 0);
+
+	put_net(w->net);
+	kfree(w);
+	atomic_dec(&v6_worker_count);
+	module_put(THIS_MODULE);
+}
+
+/* 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;
+	struct masq_dev_work *w;
+	struct net *net;
+
+	if (event != NETDEV_DOWN || atomic_read(&v6_worker_count) >= 16)
+		return NOTIFY_DONE;
+
+	dev = ifa->idev->dev;
+	net = maybe_get_net(dev_net(dev));
+	if (!net)
+		return NOTIFY_DONE;
+
+	if (!try_module_get(THIS_MODULE))
+		goto err_module;
+
+	w = kmalloc(sizeof(*w), GFP_ATOMIC);
+	if (w) {
+		atomic_inc(&v6_worker_count);
+
+		INIT_WORK(&w->work, iterate_cleanup_work);
+		w->ifindex = dev->ifindex;
+		w->net = net;
+		w->addr = ifa->addr;
+		schedule_work(&w->work);
+
+		return NOTIFY_DONE;
+	}
+
+	module_put(THIS_MODULE);
+ err_module:
+	put_net(net);
+	return NOTIFY_DONE;
+}
+
+static struct notifier_block masq_inet6_notifier = {
+	.notifier_call	= masq_inet6_event,
+};
+
+int nf_nat_masquerade_ipv6_register_notifier(void)
+{
+	int ret = 0;
+
+	mutex_lock(&masq_mutex);
+	/* check if the notifier is already set */
+	if (++masq_refcnt > 1)
+		goto out_unlock;
+
+	ret = register_netdevice_notifier(&masq_dev_notifier);
+	if (ret)
+		goto err_dec;
+
+	ret = register_inet6addr_notifier(&masq_inet6_notifier);
+	if (ret)
+		goto err_unregister;
+
+	mutex_unlock(&masq_mutex);
+	return ret;
+
+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_ipv6_register_notifier);
+
+void nf_nat_masquerade_ipv6_unregister_notifier(void)
+{
+	mutex_lock(&masq_mutex);
+	/* check if the notifier still has clients */
+	if (--masq_refcnt > 0)
+		goto out_unlock;
+
+	unregister_inet6addr_notifier(&masq_inet6_notifier);
+	unregister_netdevice_notifier(&masq_dev_notifier);
+out_unlock:
+	mutex_unlock(&masq_mutex);
+}
+EXPORT_SYMBOL_GPL(nf_nat_masquerade_ipv6_unregister_notifier);
+#endif