/*
 *      xt_hashlimit - Netfilter module to limit the number of packets per time
 *      separately for each hashbucket (sourceip/sourceport/dstip/dstport)
 *
 *      (C) 2003-2004 by Harald Welte <laforge@netfilter.org>
 *      (C) 2006-2012 Patrick McHardy <kaber@trash.net>
 *      Copyright © CC Computer Consultants GmbH, 2007 - 2008
 *
 * Development of this code was funded by Astaro AG, http://www.astaro.com/
 */
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/module.h>
#include <linux/spinlock.h>
#include <linux/random.h>
#include <linux/jhash.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/list.h>
#include <linux/skbuff.h>
#include <linux/mm.h>
#include <linux/in.h>
#include <linux/ip.h>
#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
#include <linux/ipv6.h>
#include <net/ipv6.h>
#endif

#include <net/net_namespace.h>
#include <net/netns/generic.h>

#include <linux/netfilter/x_tables.h>
#include <linux/netfilter_ipv4/ip_tables.h>
#include <linux/netfilter_ipv6/ip6_tables.h>
#include <linux/netfilter/xt_hashlimit.h>
#include <linux/mutex.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");
MODULE_DESCRIPTION("Xtables: per hash-bucket rate-limit match");
MODULE_ALIAS("ipt_hashlimit");
MODULE_ALIAS("ip6t_hashlimit");

struct hashlimit_net {
        struct hlist_head       htables;
        struct proc_dir_entry   *ipt_hashlimit;
        struct proc_dir_entry   *ip6t_hashlimit;
};

static int hashlimit_net_id;
static inline struct hashlimit_net *hashlimit_pernet(struct net *net)
{
        return net_generic(net, hashlimit_net_id);
}

/* need to declare this at the top */
static const struct file_operations dl_file_ops;

/* hash table crap */
struct dsthash_dst {
        union {
                struct {
                        __be32 src;
                        __be32 dst;
                } ip;
#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
                struct {
                        __be32 src[4];
                        __be32 dst[4];
                } ip6;
#endif
        };
        __be16 src_port;
        __be16 dst_port;
};

struct dsthash_ent {
        /* static / read-only parts in the beginning */
        struct hlist_node node;
        struct dsthash_dst dst;

        /* modified structure members in the end */
        spinlock_t lock;
        unsigned long expires;          /* precalculated expiry time */
        struct {
                unsigned long prev;     /* last modification */
                u_int32_t credit;
                u_int32_t credit_cap, cost;
        } rateinfo;
        struct rcu_head rcu;
};

struct xt_hashlimit_htable {
        struct hlist_node node;         /* global list of all htables */
        int use;
        u_int8_t family;
        bool rnd_initialized;

        struct hashlimit_cfg1 cfg;      /* config */

        /* used internally */
        spinlock_t lock;                /* lock for list_head */
        u_int32_t rnd;                  /* random seed for hash */
        unsigned int count;             /* number entries in table */
        struct timer_list timer;        /* timer for gc */

        /* seq_file stuff */
        struct proc_dir_entry *pde;
        const char *name;
        struct net *net;

        struct hlist_head hash[0];      /* hashtable itself */
};

static DEFINE_MUTEX(hashlimit_mutex);   /* protects htables list */
static struct kmem_cache *hashlimit_cachep __read_mostly;

static inline bool dst_cmp(const struct dsthash_ent *ent,
                           const struct dsthash_dst *b)
{
        return !memcmp(&ent->dst, b, sizeof(ent->dst));
}

static u_int32_t
hash_dst(const struct xt_hashlimit_htable *ht, const struct dsthash_dst *dst)
{
        u_int32_t hash = jhash2((const u32 *)dst,
                                sizeof(*dst)/sizeof(u32),
                                ht->rnd);
        /*
         * Instead of returning hash % ht->cfg.size (implying a divide)
         * we return the high 32 bits of the (hash * ht->cfg.size) that will
         * give results between [0 and cfg.size-1] and same hash distribution,
         * but using a multiply, less expensive than a divide
         */
        return ((u64)hash * ht->cfg.size) >> 32;
}

static struct dsthash_ent *
dsthash_find(const struct xt_hashlimit_htable *ht,
             const struct dsthash_dst *dst)
{
        struct dsthash_ent *ent;
        u_int32_t hash = hash_dst(ht, dst);

        if (!hlist_empty(&ht->hash[hash])) {
                hlist_for_each_entry_rcu(ent, &ht->hash[hash], node)
                        if (dst_cmp(ent, dst)) {
                                spin_lock(&ent->lock);
                                return ent;
                        }
        }
        return NULL;
}

/* allocate dsthash_ent, initialize dst, put in htable and lock it */
static struct dsthash_ent *
dsthash_alloc_init(struct xt_hashlimit_htable *ht,
                   const struct dsthash_dst *dst, bool *race)
{
        struct dsthash_ent *ent;

        spin_lock(&ht->lock);

        /* Two or more packets may race to create the same entry in the
         * hashtable, double check if this packet lost race.
         */
        ent = dsthash_find(ht, dst);
        if (ent != NULL) {
                spin_unlock(&ht->lock);
                *race = true;
                return ent;
        }

        /* initialize hash with random val at the time we allocate
         * the first hashtable entry */
        if (unlikely(!ht->rnd_initialized)) {
                get_random_bytes(&ht->rnd, sizeof(ht->rnd));
                ht->rnd_initialized = true;
        }

        if (ht->cfg.max && ht->count >= ht->cfg.max) {
                /* FIXME: do something. question is what.. */
                net_err_ratelimited("max count of %u reached\n", ht->cfg.max);
                ent = NULL;
        } else
                ent = kmem_cache_alloc(hashlimit_cachep, GFP_ATOMIC);
        if (ent) {
                memcpy(&ent->dst, dst, sizeof(ent->dst));
                spin_lock_init(&ent->lock);

                spin_lock(&ent->lock);
                hlist_add_head_rcu(&ent->node, &ht->hash[hash_dst(ht, dst)]);
                ht->count++;
        }
        spin_unlock(&ht->lock);
        return ent;
}

static void dsthash_free_rcu(struct rcu_head *head)
{
        struct dsthash_ent *ent = container_of(head, struct dsthash_ent, rcu);

        kmem_cache_free(hashlimit_cachep, ent);
}

static inline void
dsthash_free(struct xt_hashlimit_htable *ht, struct dsthash_ent *ent)
{
        hlist_del_rcu(&ent->node);
        call_rcu_bh(&ent->rcu, dsthash_free_rcu);
        ht->count--;
}
static void htable_gc(unsigned long htlong);

static int htable_create(struct net *net, struct xt_hashlimit_mtinfo1 *minfo,
                         u_int8_t family)
{
        struct hashlimit_net *hashlimit_net = hashlimit_pernet(net);
        struct xt_hashlimit_htable *hinfo;
        unsigned int size;
        unsigned int i;

        if (minfo->cfg.size) {
                size = minfo->cfg.size;
        } else {
                size = (totalram_pages << PAGE_SHIFT) / 16384 /
                       sizeof(struct list_head);
                if (totalram_pages > 1024 * 1024 * 1024 / PAGE_SIZE)
                        size = 8192;
                if (size < 16)
                        size = 16;
        }
        /* FIXME: don't use vmalloc() here or anywhere else -HW */
        hinfo = vmalloc(sizeof(struct xt_hashlimit_htable) +
                        sizeof(struct list_head) * size);
        if (hinfo == NULL)
                return -ENOMEM;
        minfo->hinfo = hinfo;

        /* copy match config into hashtable config */
        memcpy(&hinfo->cfg, &minfo->cfg, sizeof(hinfo->cfg));
        hinfo->cfg.size = size;
        if (hinfo->cfg.max == 0)
                hinfo->cfg.max = 8 * hinfo->cfg.size;
        else if (hinfo->cfg.max < hinfo->cfg.size)
                hinfo->cfg.max = hinfo->cfg.size;

        for (i = 0; i < hinfo->cfg.size; i++)
                INIT_HLIST_HEAD(&hinfo->hash[i]);

        hinfo->use = 1;
        hinfo->count = 0;
        hinfo->family = family;
        hinfo->rnd_initialized = false;
        hinfo->name = kstrdup(minfo->name, GFP_KERNEL);
        if (!hinfo->name) {
                vfree(hinfo);
                return -ENOMEM;
        }
        spin_lock_init(&hinfo->lock);

        hinfo->pde = proc_create_data(minfo->name, 0,
                (family == NFPROTO_IPV4) ?
                hashlimit_net->ipt_hashlimit : hashlimit_net->ip6t_hashlimit,
                &dl_file_ops, hinfo);
        if (hinfo->pde == NULL) {
                kfree(hinfo->name);
                vfree(hinfo);
                return -ENOMEM;
        }
        hinfo->net = net;

        setup_timer(&hinfo->timer, htable_gc, (unsigned long)hinfo);
        hinfo->timer.expires = jiffies + msecs_to_jiffies(hinfo->cfg.gc_interval);
        add_timer(&hinfo->timer);

        hlist_add_head(&hinfo->node, &hashlimit_net->htables);

        return 0;
}

static bool select_all(const struct xt_hashlimit_htable *ht,
                       const struct dsthash_ent *he)
{
        return 1;
}

static bool select_gc(const struct xt_hashlimit_htable *ht,
                      const struct dsthash_ent *he)
{
        return time_after_eq(jiffies, he->expires);
}

static void htable_selective_cleanup(struct xt_hashlimit_htable *ht,
                        bool (*select)(const struct xt_hashlimit_htable *ht,
                                      const struct dsthash_ent *he))
{
        unsigned int i;

        /* lock hash table and iterate over it */
        spin_lock_bh(&ht->lock);
        for (i = 0; i < ht->cfg.size; i++) {
                struct dsthash_ent *dh;
                struct hlist_node *n;
                hlist_for_each_entry_safe(dh, n, &ht->hash[i], node) {
                        if ((*select)(ht, dh))
                                dsthash_free(ht, dh);
                }
        }
        spin_unlock_bh(&ht->lock);
}

/* hash table garbage collector, run by timer */
static void htable_gc(unsigned long htlong)
{
        struct xt_hashlimit_htable *ht = (struct xt_hashlimit_htable *)htlong;

        htable_selective_cleanup(ht, select_gc);

        /* re-add the timer accordingly */
        ht->timer.expires = jiffies + msecs_to_jiffies(ht->cfg.gc_interval);
        add_timer(&ht->timer);
}

static void htable_destroy(struct xt_hashlimit_htable *hinfo)
{
        struct hashlimit_net *hashlimit_net = hashlimit_pernet(hinfo->net);
        struct proc_dir_entry *parent;

        del_timer_sync(&hinfo->timer);

        if (hinfo->family == NFPROTO_IPV4)
                parent = hashlimit_net->ipt_hashlimit;
        else
                parent = hashlimit_net->ip6t_hashlimit;

        if(parent != NULL)
                remove_proc_entry(hinfo->name, parent);

        htable_selective_cleanup(hinfo, select_all);
        kfree(hinfo->name);
        vfree(hinfo);
}

static struct xt_hashlimit_htable *htable_find_get(struct net *net,
                                                   const char *name,
                                                   u_int8_t family)
{
        struct hashlimit_net *hashlimit_net = hashlimit_pernet(net);
        struct xt_hashlimit_htable *hinfo;

        hlist_for_each_entry(hinfo, &hashlimit_net->htables, node) {
                if (!strcmp(name, hinfo->name) &&
                    hinfo->family == family) {
                        hinfo->use++;
                        return hinfo;
                }
        }
        return NULL;
}

static void htable_put(struct xt_hashlimit_htable *hinfo)
{
        mutex_lock(&hashlimit_mutex);
        if (--hinfo->use == 0) {
                hlist_del(&hinfo->node);
                htable_destroy(hinfo);
        }
        mutex_unlock(&hashlimit_mutex);
}

/* The algorithm used is the Simple Token Bucket Filter (TBF)
 * see net/sched/sch_tbf.c in the linux source tree
 */

/* Rusty: This is my (non-mathematically-inclined) understanding of
   this algorithm.  The `average rate' in jiffies becomes your initial
   amount of credit `credit' and the most credit you can ever have
   `credit_cap'.  The `peak rate' becomes the cost of passing the
   test, `cost'.

   `prev' tracks the last packet hit: you gain one credit per jiffy.
   If you get credit balance more than this, the extra credit is
   discarded.  Every time the match passes, you lose `cost' credits;
   if you don't have that many, the test fails.

   See Alexey's formal explanation in net/sched/sch_tbf.c.

   To get the maximum range, we multiply by this factor (ie. you get N
   credits per jiffy).  We want to allow a rate as low as 1 per day
   (slowest userspace tool allows), which means
   CREDITS_PER_JIFFY*HZ*60*60*24 < 2^32 ie.
*/
#define MAX_CPJ (0xFFFFFFFF / (HZ*60*60*24))

/* Repeated shift and or gives us all 1s, final shift and add 1 gives
 * us the power of 2 below the theoretical max, so GCC simply does a
 * shift. */
#define _POW2_BELOW2(x) ((x)|((x)>>1))
#define _POW2_BELOW4(x) (_POW2_BELOW2(x)|_POW2_BELOW2((x)>>2))
#define _POW2_BELOW8(x) (_POW2_BELOW4(x)|_POW2_BELOW4((x)>>4))
#define _POW2_BELOW16(x) (_POW2_BELOW8(x)|_POW2_BELOW8((x)>>8))
#define _POW2_BELOW32(x) (_POW2_BELOW16(x)|_POW2_BELOW16((x)>>16))
#define POW2_BELOW32(x) ((_POW2_BELOW32(x)>>1) + 1)

#define CREDITS_PER_JIFFY POW2_BELOW32(MAX_CPJ)

/* in byte mode, the lowest possible rate is one packet/second.
 * credit_cap is used as a counter that tells us how many times we can
 * refill the "credits available" counter when it becomes empty.
 */
#define MAX_CPJ_BYTES (0xFFFFFFFF / HZ)
#define CREDITS_PER_JIFFY_BYTES POW2_BELOW32(MAX_CPJ_BYTES)

static u32 xt_hashlimit_len_to_chunks(u32 len)
{
        return (len >> XT_HASHLIMIT_BYTE_SHIFT) + 1;
}

/* Precision saver. */
static u32 user2credits(u32 user)
{
        /* If multiplying would overflow... */
        if (user > 0xFFFFFFFF / (HZ*CREDITS_PER_JIFFY))
                /* Divide first. */
                return (user / XT_HASHLIMIT_SCALE) * HZ * CREDITS_PER_JIFFY;

        return (user * HZ * CREDITS_PER_JIFFY) / XT_HASHLIMIT_SCALE;
}

static u32 user2credits_byte(u32 user)
{
        u64 us = user;
        us *= HZ * CREDITS_PER_JIFFY_BYTES;
        return (u32) (us >> 32);
}

static void rateinfo_recalc(struct dsthash_ent *dh, unsigned long now, u32 mode)
{
        unsigned long delta = now - dh->rateinfo.prev;
        u32 cap;

        if (delta == 0)
                return;

        dh->rateinfo.prev = now;

        if (mode & XT_HASHLIMIT_BYTES) {
                u32 tmp = dh->rateinfo.credit;
                dh->rateinfo.credit += CREDITS_PER_JIFFY_BYTES * delta;
                cap = CREDITS_PER_JIFFY_BYTES * HZ;
                if (tmp >= dh->rateinfo.credit) {/* overflow */
                        dh->rateinfo.credit = cap;
                        return;
                }
        } else {
                dh->rateinfo.credit += delta * CREDITS_PER_JIFFY;
                cap = dh->rateinfo.credit_cap;
        }
        if (dh->rateinfo.credit > cap)
                dh->rateinfo.credit = cap;
}

static void rateinfo_init(struct dsthash_ent *dh,
                          struct xt_hashlimit_htable *hinfo)
{
        dh->rateinfo.prev = jiffies;
        if (hinfo->cfg.mode & XT_HASHLIMIT_BYTES) {
                dh->rateinfo.credit = CREDITS_PER_JIFFY_BYTES * HZ;
                dh->rateinfo.cost = user2credits_byte(hinfo->cfg.avg);
                dh->rateinfo.credit_cap = hinfo->cfg.burst;
        } else {
                dh->rateinfo.credit = user2credits(hinfo->cfg.avg *
                                                   hinfo->cfg.burst);
                dh->rateinfo.cost = user2credits(hinfo->cfg.avg);
                dh->rateinfo.credit_cap = dh->rateinfo.credit;
        }
}

static inline __be32 maskl(__be32 a, unsigned int l)
{
        return l ? htonl(ntohl(a) & ~0 << (32 - l)) : 0;
}

#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
static void hashlimit_ipv6_mask(__be32 *i, unsigned int p)
{
        switch (p) {
        case 0 ... 31:
                i[0] = maskl(i[0], p);
                i[1] = i[2] = i[3] = 0;
                break;
        case 32 ... 63:
                i[1] = maskl(i[1], p - 32);
                i[2] = i[3] = 0;
                break;
        case 64 ... 95:
                i[2] = maskl(i[2], p - 64);
                i[3] = 0;
                break;
        case 96 ... 127:
                i[3] = maskl(i[3], p - 96);
                break;
        case 128:
                break;
        }
}
#endif

static int
hashlimit_init_dst(const struct xt_hashlimit_htable *hinfo,
                   struct dsthash_dst *dst,
                   const struct sk_buff *skb, unsigned int protoff)
{
        __be16 _ports[2], *ports;
        u8 nexthdr;
        int poff;

        memset(dst, 0, sizeof(*dst));

        switch (hinfo->family) {
        case NFPROTO_IPV4:
                if (hinfo->cfg.mode & XT_HASHLIMIT_HASH_DIP)
                        dst->ip.dst = maskl(ip_hdr(skb)->daddr,
                                      hinfo->cfg.dstmask);
                if (hinfo->cfg.mode & XT_HASHLIMIT_HASH_SIP)
                        dst->ip.src = maskl(ip_hdr(skb)->saddr,
                                      hinfo->cfg.srcmask);

                if (!(hinfo->cfg.mode &
                      (XT_HASHLIMIT_HASH_DPT | XT_HASHLIMIT_HASH_SPT)))
                        return 0;
                nexthdr = ip_hdr(skb)->protocol;
                break;
#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
        case NFPROTO_IPV6:
        {
                __be16 frag_off;

                if (hinfo->cfg.mode & XT_HASHLIMIT_HASH_DIP) {
                        memcpy(&dst->ip6.dst, &ipv6_hdr(skb)->daddr,
                               sizeof(dst->ip6.dst));
                        hashlimit_ipv6_mask(dst->ip6.dst, hinfo->cfg.dstmask);
                }
                if (hinfo->cfg.mode & XT_HASHLIMIT_HASH_SIP) {
                        memcpy(&dst->ip6.src, &ipv6_hdr(skb)->saddr,
                               sizeof(dst->ip6.src));
                        hashlimit_ipv6_mask(dst->ip6.src, hinfo->cfg.srcmask);
                }

                if (!(hinfo->cfg.mode &
                      (XT_HASHLIMIT_HASH_DPT | XT_HASHLIMIT_HASH_SPT)))
                        return 0;
                nexthdr = ipv6_hdr(skb)->nexthdr;
                protoff = ipv6_skip_exthdr(skb, sizeof(struct ipv6hdr), &nexthdr, &frag_off);
                if ((int)protoff < 0)
                        return -1;
                break;
        }
#endif
        default:
                BUG();
                return 0;
        }

        poff = proto_ports_offset(nexthdr);
        if (poff >= 0) {
                ports = skb_header_pointer(skb, protoff + poff, sizeof(_ports),
                                           &_ports);
        } else {
                _ports[0] = _ports[1] = 0;
                ports = _ports;
        }
        if (!ports)
                return -1;
        if (hinfo->cfg.mode & XT_HASHLIMIT_HASH_SPT)
                dst->src_port = ports[0];
        if (hinfo->cfg.mode & XT_HASHLIMIT_HASH_DPT)
                dst->dst_port = ports[1];
        return 0;
}

static u32 hashlimit_byte_cost(unsigned int len, struct dsthash_ent *dh)
{
        u64 tmp = xt_hashlimit_len_to_chunks(len);
        tmp = tmp * dh->rateinfo.cost;

        if (unlikely(tmp > CREDITS_PER_JIFFY_BYTES * HZ))
                tmp = CREDITS_PER_JIFFY_BYTES * HZ;

        if (dh->rateinfo.credit < tmp && dh->rateinfo.credit_cap) {
                dh->rateinfo.credit_cap--;
                dh->rateinfo.credit = CREDITS_PER_JIFFY_BYTES * HZ;
        }
        return (u32) tmp;
}

static bool
hashlimit_mt(const struct sk_buff *skb, struct xt_action_param *par)
{
        const struct xt_hashlimit_mtinfo1 *info = par->matchinfo;
        struct xt_hashlimit_htable *hinfo = info->hinfo;
        unsigned long now = jiffies;
        struct dsthash_ent *dh;
        struct dsthash_dst dst;
        bool race = false;
        u32 cost;

        if (hashlimit_init_dst(hinfo, &dst, skb, par->thoff) < 0)
                goto hotdrop;

        rcu_read_lock_bh();
        dh = dsthash_find(hinfo, &dst);
        if (dh == NULL) {
                dh = dsthash_alloc_init(hinfo, &dst, &race);
                if (dh == NULL) {
                        rcu_read_unlock_bh();
                        goto hotdrop;
                } else if (race) {
                        /* Already got an entry, update expiration timeout */
                        dh->expires = now + msecs_to_jiffies(hinfo->cfg.expire);
                        rateinfo_recalc(dh, now, hinfo->cfg.mode);
                } else {
                        dh->expires = jiffies + msecs_to_jiffies(hinfo->cfg.expire);
                        rateinfo_init(dh, hinfo);
                }
        } else {
                /* update expiration timeout */
                dh->expires = now + msecs_to_jiffies(hinfo->cfg.expire);
                rateinfo_recalc(dh, now, hinfo->cfg.mode);
        }

        if (info->cfg.mode & XT_HASHLIMIT_BYTES)
                cost = hashlimit_byte_cost(skb->len, dh);
        else
                cost = dh->rateinfo.cost;

        if (dh->rateinfo.credit >= cost) {
                /* below the limit */
                dh->rateinfo.credit -= cost;
                spin_unlock(&dh->lock);
                rcu_read_unlock_bh();
                return !(info->cfg.mode & XT_HASHLIMIT_INVERT);
        }

        spin_unlock(&dh->lock);
        rcu_read_unlock_bh();
        /* default match is underlimit - so over the limit, we need to invert */
        return info->cfg.mode & XT_HASHLIMIT_INVERT;

 hotdrop:
        par->hotdrop = true;
        return false;
}

static int hashlimit_mt_check(const struct xt_mtchk_param *par)
{
        struct net *net = par->net;
        struct xt_hashlimit_mtinfo1 *info = par->matchinfo;
        int ret;

        if (info->cfg.gc_interval == 0 || info->cfg.expire == 0)
                return -EINVAL;
        if (info->name[sizeof(info->name)-1] != '\0')
                return -EINVAL;
        if (par->family == NFPROTO_IPV4) {
                if (info->cfg.srcmask > 32 || info->cfg.dstmask > 32)
                        return -EINVAL;
        } else {
                if (info->cfg.srcmask > 128 || info->cfg.dstmask > 128)
                        return -EINVAL;
        }

        if (info->cfg.mode & ~XT_HASHLIMIT_ALL) {
                pr_info("Unknown mode mask %X, kernel too old?\n",
                                                info->cfg.mode);
                return -EINVAL;
        }

        /* Check for overflow. */
        if (info->cfg.mode & XT_HASHLIMIT_BYTES) {
                if (user2credits_byte(info->cfg.avg) == 0) {
                        pr_info("overflow, rate too high: %u\n", info->cfg.avg);
                        return -EINVAL;
                }
        } else if (info->cfg.burst == 0 ||
                    user2credits(info->cfg.avg * info->cfg.burst) <
                    user2credits(info->cfg.avg)) {
                        pr_info("overflow, try lower: %u/%u\n",
                                info->cfg.avg, info->cfg.burst);
                        return -ERANGE;
        }

        mutex_lock(&hashlimit_mutex);
        info->hinfo = htable_find_get(net, info->name, par->family);
        if (info->hinfo == NULL) {
                ret = htable_create(net, info, par->family);
                if (ret < 0) {
                        mutex_unlock(&hashlimit_mutex);
                        return ret;
                }
        }
        mutex_unlock(&hashlimit_mutex);
        return 0;
}

static void hashlimit_mt_destroy(const struct xt_mtdtor_param *par)
{
        const struct xt_hashlimit_mtinfo1 *info = par->matchinfo;

        htable_put(info->hinfo);
}

static struct xt_match hashlimit_mt_reg[] __read_mostly = {
        {
                .name           = "hashlimit",
                .revision       = 1,
                .family         = NFPROTO_IPV4,
                .match          = hashlimit_mt,
                .matchsize      = sizeof(struct xt_hashlimit_mtinfo1),
                .checkentry     = hashlimit_mt_check,
                .destroy        = hashlimit_mt_destroy,
                .me             = THIS_MODULE,
        },
#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
        {
                .name           = "hashlimit",
                .revision       = 1,
                .family         = NFPROTO_IPV6,
                .match          = hashlimit_mt,
                .matchsize      = sizeof(struct xt_hashlimit_mtinfo1),
                .checkentry     = hashlimit_mt_check,
                .destroy        = hashlimit_mt_destroy,
                .me             = THIS_MODULE,
        },
#endif
};

/* PROC stuff */
static void *dl_seq_start(struct seq_file *s, loff_t *pos)
        __acquires(htable->lock)
{
        struct xt_hashlimit_htable *htable = s->private;
        unsigned int *bucket;

        spin_lock_bh(&htable->lock);
        if (*pos >= htable->cfg.size)
                return NULL;

        bucket = kmalloc(sizeof(unsigned int), GFP_ATOMIC);
        if (!bucket)
                return ERR_PTR(-ENOMEM);

        *bucket = *pos;
        return bucket;
}

static void *dl_seq_next(struct seq_file *s, void *v, loff_t *pos)
{
        struct xt_hashlimit_htable *htable = s->private;
        unsigned int *bucket = (unsigned int *)v;

        *pos = ++(*bucket);
        if (*pos >= htable->cfg.size) {
                kfree(v);
                return NULL;
        }
        return bucket;
}

static void dl_seq_stop(struct seq_file *s, void *v)
        __releases(htable->lock)
{
        struct xt_hashlimit_htable *htable = s->private;
        unsigned int *bucket = (unsigned int *)v;

        if (!IS_ERR(bucket))
                kfree(bucket);
        spin_unlock_bh(&htable->lock);
}

static int dl_seq_real_show(struct dsthash_ent *ent, u_int8_t family,
                                   struct seq_file *s)
{
        int res;
        const struct xt_hashlimit_htable *ht = s->private;

        spin_lock(&ent->lock);
        /* recalculate to show accurate numbers */
        rateinfo_recalc(ent, jiffies, ht->cfg.mode);

        switch (family) {
        case NFPROTO_IPV4:
                res = seq_printf(s, "%ld %pI4:%u->%pI4:%u %u %u %u\n",
                                 (long)(ent->expires - jiffies)/HZ,
                                 &ent->dst.ip.src,
                                 ntohs(ent->dst.src_port),
                                 &ent->dst.ip.dst,
                                 ntohs(ent->dst.dst_port),
                                 ent->rateinfo.credit, ent->rateinfo.credit_cap,
                                 ent->rateinfo.cost);
                break;
#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
        case NFPROTO_IPV6:
                res = seq_printf(s, "%ld %pI6:%u->%pI6:%u %u %u %u\n",
                                 (long)(ent->expires - jiffies)/HZ,
                                 &ent->dst.ip6.src,
                                 ntohs(ent->dst.src_port),
                                 &ent->dst.ip6.dst,
                                 ntohs(ent->dst.dst_port),
                                 ent->rateinfo.credit, ent->rateinfo.credit_cap,
                                 ent->rateinfo.cost);
                break;
#endif
        default:
                BUG();
                res = 0;
        }
        spin_unlock(&ent->lock);
        return res;
}

static int dl_seq_show(struct seq_file *s, void *v)
{
        struct xt_hashlimit_htable *htable = s->private;
        unsigned int *bucket = (unsigned int *)v;
        struct dsthash_ent *ent;

        if (!hlist_empty(&htable->hash[*bucket])) {
                hlist_for_each_entry(ent, &htable->hash[*bucket], node)
                        if (dl_seq_real_show(ent, htable->family, s))
                                return -1;
        }
        return 0;
}

static const struct seq_operations dl_seq_ops = {
        .start = dl_seq_start,
        .next  = dl_seq_next,
        .stop  = dl_seq_stop,
        .show  = dl_seq_show
};

static int dl_proc_open(struct inode *inode, struct file *file)
{
        int ret = seq_open(file, &dl_seq_ops);

        if (!ret) {
                struct seq_file *sf = file->private_data;
                sf->private = PDE_DATA(inode);
        }
        return ret;
}

static const struct file_operations dl_file_ops = {
        .owner   = THIS_MODULE,
        .open    = dl_proc_open,
        .read    = seq_read,
        .llseek  = seq_lseek,
        .release = seq_release
};

static int __net_init hashlimit_proc_net_init(struct net *net)
{
        struct hashlimit_net *hashlimit_net = hashlimit_pernet(net);

        hashlimit_net->ipt_hashlimit = proc_mkdir("ipt_hashlimit", net->proc_net);
        if (!hashlimit_net->ipt_hashlimit)
                return -ENOMEM;
#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
        hashlimit_net->ip6t_hashlimit = proc_mkdir("ip6t_hashlimit", net->proc_net);
        if (!hashlimit_net->ip6t_hashlimit) {
                remove_proc_entry("ipt_hashlimit", net->proc_net);
                return -ENOMEM;
        }
#endif
        return 0;
}

static void __net_exit hashlimit_proc_net_exit(struct net *net)
{
        struct xt_hashlimit_htable *hinfo;
        struct proc_dir_entry *pde;
        struct hashlimit_net *hashlimit_net = hashlimit_pernet(net);

        /* recent_net_exit() is called before recent_mt_destroy(). Make sure
         * that the parent xt_recent proc entry is is empty before trying to
         * remove it.
         */
        mutex_lock(&hashlimit_mutex);
        pde = hashlimit_net->ipt_hashlimit;
        if (pde == NULL)
                pde = hashlimit_net->ip6t_hashlimit;

        hlist_for_each_entry(hinfo, &hashlimit_net->htables, node)
                remove_proc_entry(hinfo->name, pde);

        hashlimit_net->ipt_hashlimit = NULL;
        hashlimit_net->ip6t_hashlimit = NULL;
        mutex_unlock(&hashlimit_mutex);

        remove_proc_entry("ipt_hashlimit", net->proc_net);
#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
        remove_proc_entry("ip6t_hashlimit", net->proc_net);
#endif
}

static int __net_init hashlimit_net_init(struct net *net)
{
        struct hashlimit_net *hashlimit_net = hashlimit_pernet(net);

        INIT_HLIST_HEAD(&hashlimit_net->htables);
        return hashlimit_proc_net_init(net);
}

static void __net_exit hashlimit_net_exit(struct net *net)
{
        hashlimit_proc_net_exit(net);
}

static struct pernet_operations hashlimit_net_ops = {
        .init   = hashlimit_net_init,
        .exit   = hashlimit_net_exit,
        .id     = &hashlimit_net_id,
        .size   = sizeof(struct hashlimit_net),
};

static int __init hashlimit_mt_init(void)
{
        int err;

        err = register_pernet_subsys(&hashlimit_net_ops);
        if (err < 0)
                return err;
        err = xt_register_matches(hashlimit_mt_reg,
              ARRAY_SIZE(hashlimit_mt_reg));
        if (err < 0)
                goto err1;

        err = -ENOMEM;
        hashlimit_cachep = kmem_cache_create("xt_hashlimit",
                                            sizeof(struct dsthash_ent), 0, 0,
                                            NULL);
        if (!hashlimit_cachep) {
                pr_warning("unable to create slab cache\n");
                goto err2;
        }
        return 0;

err2:
        xt_unregister_matches(hashlimit_mt_reg, ARRAY_SIZE(hashlimit_mt_reg));
err1:
        unregister_pernet_subsys(&hashlimit_net_ops);
        return err;

}

static void __exit hashlimit_mt_exit(void)
{
        xt_unregister_matches(hashlimit_mt_reg, ARRAY_SIZE(hashlimit_mt_reg));
        unregister_pernet_subsys(&hashlimit_net_ops);

        rcu_barrier_bh();
        kmem_cache_destroy(hashlimit_cachep);
}

module_init(hashlimit_mt_init);
module_exit(hashlimit_mt_exit);