// SPDX-License-Identifier: GPL-2.0-only
/* Event cache for netfilter. */

/*
 * (C) 2005 Harald Welte <laforge@gnumonks.org>
 * (C) 2005 Patrick McHardy <kaber@trash.net>
 * (C) 2005-2006 Netfilter Core Team <coreteam@netfilter.org>
 * (C) 2005 USAGI/WIDE Project <http://www.linux-ipv6.org>
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/types.h>
#include <linux/netfilter.h>
#include <linux/skbuff.h>
#include <linux/vmalloc.h>
#include <linux/stddef.h>
#include <linux/err.h>
#include <linux/percpu.h>
#include <linux/kernel.h>
#include <linux/netdevice.h>
#include <linux/slab.h>
#include <linux/export.h>

#include <net/netfilter/nf_conntrack.h>
#include <net/netfilter/nf_conntrack_core.h>
#include <net/netfilter/nf_conntrack_ecache.h>
#include <net/netfilter/nf_conntrack_extend.h>

static DEFINE_MUTEX(nf_ct_ecache_mutex);

#define ECACHE_RETRY_WAIT (HZ/10)
#define ECACHE_STACK_ALLOC (256 / sizeof(void *))

enum retry_state {
        STATE_CONGESTED,
        STATE_RESTART,
        STATE_DONE,
};

static enum retry_state ecache_work_evict_list(struct ct_pcpu *pcpu)
{
        struct nf_conn *refs[ECACHE_STACK_ALLOC];
        enum retry_state ret = STATE_DONE;
        struct nf_conntrack_tuple_hash *h;
        struct hlist_nulls_node *n;
        unsigned int evicted = 0;

        spin_lock(&pcpu->lock);

        hlist_nulls_for_each_entry(h, n, &pcpu->dying, hnnode) {
                struct nf_conn *ct = nf_ct_tuplehash_to_ctrack(h);
                struct nf_conntrack_ecache *e;

                if (!nf_ct_is_confirmed(ct))
                        continue;

                /* This ecache access is safe because the ct is on the
                 * pcpu dying list and we hold the spinlock -- the entry
                 * cannot be free'd until after the lock is released.
                 *
                 * This is true even if ct has a refcount of 0: the
                 * cpu that is about to free the entry must remove it
                 * from the dying list and needs the lock to do so.
                 */
                e = nf_ct_ecache_find(ct);
                if (!e || e->state != NFCT_ECACHE_DESTROY_FAIL)
                        continue;

                /* ct is in NFCT_ECACHE_DESTROY_FAIL state, this means
                 * the worker owns this entry: the ct will remain valid
                 * until the worker puts its ct reference.
                 */
                if (nf_conntrack_event(IPCT_DESTROY, ct)) {
                        ret = STATE_CONGESTED;
                        break;
                }

                e->state = NFCT_ECACHE_DESTROY_SENT;
                refs[evicted] = ct;

                if (++evicted >= ARRAY_SIZE(refs)) {
                        ret = STATE_RESTART;
                        break;
                }
        }

        spin_unlock(&pcpu->lock);

        /* can't _put while holding lock */
        while (evicted)
                nf_ct_put(refs[--evicted]);

        return ret;
}

static void ecache_work(struct work_struct *work)
{
        struct nf_conntrack_net *cnet = container_of(work, struct nf_conntrack_net, ecache_dwork.work);
        struct netns_ct *ctnet = cnet->ct_net;
        int cpu, delay = -1;
        struct ct_pcpu *pcpu;

        local_bh_disable();

        for_each_possible_cpu(cpu) {
                enum retry_state ret;

                pcpu = per_cpu_ptr(ctnet->pcpu_lists, cpu);

                ret = ecache_work_evict_list(pcpu);

                switch (ret) {
                case STATE_CONGESTED:
                        delay = ECACHE_RETRY_WAIT;
                        goto out;
                case STATE_RESTART:
                        delay = 0;
                        break;
                case STATE_DONE:
                        break;
                }
        }

 out:
        local_bh_enable();

        ctnet->ecache_dwork_pending = delay > 0;
        if (delay >= 0)
                schedule_delayed_work(&cnet->ecache_dwork, delay);
}

static int __nf_conntrack_eventmask_report(struct nf_conntrack_ecache *e,
                                           const unsigned int events,
                                           const unsigned long missed,
                                           const struct nf_ct_event *item)
{
        struct nf_conn *ct = item->ct;
        struct net *net = nf_ct_net(item->ct);
        struct nf_ct_event_notifier *notify;
        int ret;

        if (!((events | missed) & e->ctmask))
                return 0;

        rcu_read_lock();

        notify = rcu_dereference(net->ct.nf_conntrack_event_cb);
        if (!notify) {
                rcu_read_unlock();
                return 0;
        }

        ret = notify->ct_event(events | missed, item);
        rcu_read_unlock();

        if (likely(ret >= 0 && missed == 0))
                return 0;

        spin_lock_bh(&ct->lock);
        if (ret < 0)
                e->missed |= events;
        else
                e->missed &= ~missed;
        spin_unlock_bh(&ct->lock);

        return ret;
}

int nf_conntrack_eventmask_report(unsigned int events, struct nf_conn *ct,
                                  u32 portid, int report)
{
        struct nf_conntrack_ecache *e;
        struct nf_ct_event item;
        unsigned long missed;
        int ret;

        if (!nf_ct_is_confirmed(ct))
                return 0;

        e = nf_ct_ecache_find(ct);
        if (!e)
                return 0;

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

        item.ct = ct;
        item.portid = e->portid ? e->portid : portid;
        item.report = report;

        /* This is a resent of a destroy event? If so, skip missed */
        missed = e->portid ? 0 : e->missed;

        ret = __nf_conntrack_eventmask_report(e, events, missed, &item);
        if (unlikely(ret < 0 && (events & (1 << IPCT_DESTROY)))) {
                /* This is a destroy event that has been triggered by a process,
                 * we store the PORTID to include it in the retransmission.
                 */
                if (e->portid == 0 && portid != 0)
                        e->portid = portid;
                e->state = NFCT_ECACHE_DESTROY_FAIL;
        }

        return ret;
}
EXPORT_SYMBOL_GPL(nf_conntrack_eventmask_report);

/* deliver cached events and clear cache entry - must be called with locally
 * disabled softirqs */
void nf_ct_deliver_cached_events(struct nf_conn *ct)
{
        struct nf_conntrack_ecache *e;
        struct nf_ct_event item;
        unsigned long events;

        if (!nf_ct_is_confirmed(ct) || nf_ct_is_dying(ct))
                return;

        e = nf_ct_ecache_find(ct);
        if (e == NULL)
                return;

        events = xchg(&e->cache, 0);

        item.ct = ct;
        item.portid = 0;
        item.report = 0;

        /* We make a copy of the missed event cache without taking
         * the lock, thus we may send missed events twice. However,
         * this does not harm and it happens very rarely.
         */
        __nf_conntrack_eventmask_report(e, events, e->missed, &item);
}
EXPORT_SYMBOL_GPL(nf_ct_deliver_cached_events);

void nf_ct_expect_event_report(enum ip_conntrack_expect_events event,
                               struct nf_conntrack_expect *exp,
                               u32 portid, int report)

{
        struct net *net = nf_ct_exp_net(exp);
        struct nf_ct_event_notifier *notify;
        struct nf_conntrack_ecache *e;

        rcu_read_lock();
        notify = rcu_dereference(net->ct.nf_conntrack_event_cb);
        if (!notify)
                goto out_unlock;

        e = nf_ct_ecache_find(exp->master);
        if (!e)
                goto out_unlock;

        if (e->expmask & (1 << event)) {
                struct nf_exp_event item = {
                        .exp    = exp,
                        .portid = portid,
                        .report = report
                };
                notify->exp_event(1 << event, &item);
        }
out_unlock:
        rcu_read_unlock();
}

void nf_conntrack_register_notifier(struct net *net,
                                    const struct nf_ct_event_notifier *new)
{
        struct nf_ct_event_notifier *notify;

        mutex_lock(&nf_ct_ecache_mutex);
        notify = rcu_dereference_protected(net->ct.nf_conntrack_event_cb,
                                           lockdep_is_held(&nf_ct_ecache_mutex));
        WARN_ON_ONCE(notify);
        rcu_assign_pointer(net->ct.nf_conntrack_event_cb, new);
        mutex_unlock(&nf_ct_ecache_mutex);
}
EXPORT_SYMBOL_GPL(nf_conntrack_register_notifier);

void nf_conntrack_unregister_notifier(struct net *net)
{
        mutex_lock(&nf_ct_ecache_mutex);
        RCU_INIT_POINTER(net->ct.nf_conntrack_event_cb, NULL);
        mutex_unlock(&nf_ct_ecache_mutex);
        /* synchronize_rcu() is called after netns pre_exit */
}
EXPORT_SYMBOL_GPL(nf_conntrack_unregister_notifier);

void nf_conntrack_ecache_work(struct net *net, enum nf_ct_ecache_state state)
{
        struct nf_conntrack_net *cnet = nf_ct_pernet(net);

        if (state == NFCT_ECACHE_DESTROY_FAIL &&
            !delayed_work_pending(&cnet->ecache_dwork)) {
                schedule_delayed_work(&cnet->ecache_dwork, HZ);
                net->ct.ecache_dwork_pending = true;
        } else if (state == NFCT_ECACHE_DESTROY_SENT) {
                net->ct.ecache_dwork_pending = false;
                mod_delayed_work(system_wq, &cnet->ecache_dwork, 0);
        }
}

#define NF_CT_EVENTS_DEFAULT 1
static int nf_ct_events __read_mostly = NF_CT_EVENTS_DEFAULT;

static const struct nf_ct_ext_type event_extend = {
        .len    = sizeof(struct nf_conntrack_ecache),
        .align  = __alignof__(struct nf_conntrack_ecache),
        .id     = NF_CT_EXT_ECACHE,
};

void nf_conntrack_ecache_pernet_init(struct net *net)
{
        struct nf_conntrack_net *cnet = nf_ct_pernet(net);

        net->ct.sysctl_events = nf_ct_events;
        cnet->ct_net = &net->ct;
        INIT_DELAYED_WORK(&cnet->ecache_dwork, ecache_work);
}

void nf_conntrack_ecache_pernet_fini(struct net *net)
{
        struct nf_conntrack_net *cnet = nf_ct_pernet(net);

        cancel_delayed_work_sync(&cnet->ecache_dwork);
}

int nf_conntrack_ecache_init(void)
{
        int ret = nf_ct_extend_register(&event_extend);
        if (ret < 0)
                pr_err("Unable to register event extension\n");

        BUILD_BUG_ON(__IPCT_MAX >= 16); /* ctmask, missed use u16 */

        return ret;
}

void nf_conntrack_ecache_fini(void)
{
        nf_ct_extend_unregister(&event_extend);
}