xt_hashlimit.c

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/*
 *  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 <[email protected]>
 *  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 <[email protected]>");
MODULE_AUTHOR("Jan Engelhardt <[email protected]>");
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;
    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;
    struct hlist_node *pos;
    u_int32_t hash = hash_dst(ht, dst);

    if (!hlist_empty(&ht->hash[hash])) {
        hlist_for_each_entry_rcu(ent, pos, &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)
{
    struct dsthash_ent *ent;

    spin_lock(&ht->lock);
    /* 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;
    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) {
        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 *pos, *n;
        hlist_for_each_entry_safe(dh, pos, 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;
    remove_proc_entry(hinfo->pde->name, parent);
    htable_selective_cleanup(hinfo, select_all);
    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;
    struct hlist_node *pos;

    hlist_for_each_entry(hinfo, pos, &hashlimit_net->htables, node) {
        if (!strcmp(name, hinfo->pde->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;
    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);
        if (dh == NULL) {
            rcu_read_unlock_bh();
            goto hotdrop;
        }
        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;
    struct hlist_node *pos;

    if (!hlist_empty(&htable->hash[*bucket])) {
        hlist_for_each_entry(ent, pos, &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(inode)->data;
    }
    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) {
        proc_net_remove(net, "ipt_hashlimit");
        return -ENOMEM;
    }
#endif
    return 0;
}

static void __net_exit hashlimit_proc_net_exit(struct net *net)
{
    proc_net_remove(net, "ipt_hashlimit");
#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
    proc_net_remove(net, "ip6t_hashlimit");
#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)
{
    struct hashlimit_net *hashlimit_net = hashlimit_pernet(net);

    BUG_ON(!hlist_empty(&hashlimit_net->htables));
    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);