// 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 masq_dev_work *w;

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

        nf_ct_iterate_cleanup_net(w->net, w->iter, (void *)w, 0, 0);

        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);