/*
 * netfilter module to limit the number of parallel tcp
 * connections per IP address.
 *   (c) 2000 Gerd Knorr <kraxel@bytesex.org>
 *   Nov 2002: Martin Bene <martin.bene@icomedias.com>:
 *              only ignore TIME_WAIT or gone connections
 *   (C) CC Computer Consultants GmbH, 2007
 *
 * based on ...
 *
 * Kernel module to match connection tracking information.
 * GPL (C) 1999  Rusty Russell (rusty@rustcorp.com.au).
 */
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/in.h>
#include <linux/in6.h>
#include <linux/ip.h>
#include <linux/ipv6.h>
#include <linux/jhash.h>
#include <linux/slab.h>
#include <linux/list.h>
#include <linux/rbtree.h>
#include <linux/module.h>
#include <linux/random.h>
#include <linux/skbuff.h>
#include <linux/spinlock.h>
#include <linux/netfilter/nf_conntrack_tcp.h>
#include <linux/netfilter/x_tables.h>
#include <linux/netfilter/xt_connlimit.h>
#include <net/netfilter/nf_conntrack.h>
#include <net/netfilter/nf_conntrack_core.h>
#include <net/netfilter/nf_conntrack_tuple.h>
#include <net/netfilter/nf_conntrack_zones.h>

#define CONNLIMIT_SLOTS         256U

#ifdef CONFIG_LOCKDEP
#define CONNLIMIT_LOCK_SLOTS    8U
#else
#define CONNLIMIT_LOCK_SLOTS    256U
#endif

#define CONNLIMIT_GC_MAX_NODES  8

/* we will save the tuples of all connections we care about */
struct xt_connlimit_conn {
        struct hlist_node               node;
        struct nf_conntrack_tuple       tuple;
        union nf_inet_addr              addr;
};

struct xt_connlimit_rb {
        struct rb_node node;
        struct hlist_head hhead; /* connections/hosts in same subnet */
        union nf_inet_addr addr; /* search key */
};

static spinlock_t xt_connlimit_locks[CONNLIMIT_LOCK_SLOTS] __cacheline_aligned_in_smp;

struct xt_connlimit_data {
        struct rb_root climit_root4[CONNLIMIT_SLOTS];
        struct rb_root climit_root6[CONNLIMIT_SLOTS];
};

static u_int32_t connlimit_rnd __read_mostly;
static struct kmem_cache *connlimit_rb_cachep __read_mostly;
static struct kmem_cache *connlimit_conn_cachep __read_mostly;

static inline unsigned int connlimit_iphash(__be32 addr)
{
        return jhash_1word((__force __u32)addr,
                            connlimit_rnd) % CONNLIMIT_SLOTS;
}

static inline unsigned int
connlimit_iphash6(const union nf_inet_addr *addr,
                  const union nf_inet_addr *mask)
{
        union nf_inet_addr res;
        unsigned int i;

        for (i = 0; i < ARRAY_SIZE(addr->ip6); ++i)
                res.ip6[i] = addr->ip6[i] & mask->ip6[i];

        return jhash2((u32 *)res.ip6, ARRAY_SIZE(res.ip6),
                       connlimit_rnd) % CONNLIMIT_SLOTS;
}

static inline bool already_closed(const struct nf_conn *conn)
{
        if (nf_ct_protonum(conn) == IPPROTO_TCP)
                return conn->proto.tcp.state == TCP_CONNTRACK_TIME_WAIT ||
                       conn->proto.tcp.state == TCP_CONNTRACK_CLOSE;
        else
                return 0;
}

static int
same_source_net(const union nf_inet_addr *addr,
                const union nf_inet_addr *mask,
                const union nf_inet_addr *u3, u_int8_t family)
{
        if (family == NFPROTO_IPV4) {
                return ntohl(addr->ip & mask->ip) -
                       ntohl(u3->ip & mask->ip);
        } else {
                union nf_inet_addr lh, rh;
                unsigned int i;

                for (i = 0; i < ARRAY_SIZE(addr->ip6); ++i) {
                        lh.ip6[i] = addr->ip6[i] & mask->ip6[i];
                        rh.ip6[i] = u3->ip6[i] & mask->ip6[i];
                }

                return memcmp(&lh.ip6, &rh.ip6, sizeof(lh.ip6));
        }
}

static bool add_hlist(struct hlist_head *head,
                      const struct nf_conntrack_tuple *tuple,
                      const union nf_inet_addr *addr)
{
        struct xt_connlimit_conn *conn;

        conn = kmem_cache_alloc(connlimit_conn_cachep, GFP_ATOMIC);
        if (conn == NULL)
                return false;
        conn->tuple = *tuple;
        conn->addr = *addr;
        hlist_add_head(&conn->node, head);
        return true;
}

static unsigned int check_hlist(struct net *net,
                                struct hlist_head *head,
                                const struct nf_conntrack_tuple *tuple,
                                const struct nf_conntrack_zone *zone,
                                bool *addit)
{
        const struct nf_conntrack_tuple_hash *found;
        struct xt_connlimit_conn *conn;
        struct hlist_node *n;
        struct nf_conn *found_ct;
        unsigned int length = 0;

        *addit = true;
        rcu_read_lock();

        /* check the saved connections */
        hlist_for_each_entry_safe(conn, n, head, node) {
                found = nf_conntrack_find_get(net, zone, &conn->tuple);
                if (found == NULL) {
                        hlist_del(&conn->node);
                        kmem_cache_free(connlimit_conn_cachep, conn);
                        continue;
                }

                found_ct = nf_ct_tuplehash_to_ctrack(found);

                if (nf_ct_tuple_equal(&conn->tuple, tuple)) {
                        /*
                         * Just to be sure we have it only once in the list.
                         * We should not see tuples twice unless someone hooks
                         * this into a table without "-p tcp --syn".
                         */
                        *addit = false;
                } else if (already_closed(found_ct)) {
                        /*
                         * we do not care about connections which are
                         * closed already -> ditch it
                         */
                        nf_ct_put(found_ct);
                        hlist_del(&conn->node);
                        kmem_cache_free(connlimit_conn_cachep, conn);
                        continue;
                }

                nf_ct_put(found_ct);
                length++;
        }

        rcu_read_unlock();

        return length;
}

static void tree_nodes_free(struct rb_root *root,
                            struct xt_connlimit_rb *gc_nodes[],
                            unsigned int gc_count)
{
        struct xt_connlimit_rb *rbconn;

        while (gc_count) {
                rbconn = gc_nodes[--gc_count];
                rb_erase(&rbconn->node, root);
                kmem_cache_free(connlimit_rb_cachep, rbconn);
        }
}

static unsigned int
count_tree(struct net *net, struct rb_root *root,
           const struct nf_conntrack_tuple *tuple,
           const union nf_inet_addr *addr, const union nf_inet_addr *mask,
           u8 family, const struct nf_conntrack_zone *zone)
{
        struct xt_connlimit_rb *gc_nodes[CONNLIMIT_GC_MAX_NODES];
        struct rb_node **rbnode, *parent;
        struct xt_connlimit_rb *rbconn;
        struct xt_connlimit_conn *conn;
        unsigned int gc_count;
        bool no_gc = false;

 restart:
        gc_count = 0;
        parent = NULL;
        rbnode = &(root->rb_node);
        while (*rbnode) {
                int diff;
                bool addit;

                rbconn = container_of(*rbnode, struct xt_connlimit_rb, node);

                parent = *rbnode;
                diff = same_source_net(addr, mask, &rbconn->addr, family);
                if (diff < 0) {
                        rbnode = &((*rbnode)->rb_left);
                } else if (diff > 0) {
                        rbnode = &((*rbnode)->rb_right);
                } else {
                        /* same source network -> be counted! */
                        unsigned int count;
                        count = check_hlist(net, &rbconn->hhead, tuple, zone, &addit);

                        tree_nodes_free(root, gc_nodes, gc_count);
                        if (!addit)
                                return count;

                        if (!add_hlist(&rbconn->hhead, tuple, addr))
                                return 0; /* hotdrop */

                        return count + 1;
                }

                if (no_gc || gc_count >= ARRAY_SIZE(gc_nodes))
                        continue;

                /* only used for GC on hhead, retval and 'addit' ignored */
                check_hlist(net, &rbconn->hhead, tuple, zone, &addit);
                if (hlist_empty(&rbconn->hhead))
                        gc_nodes[gc_count++] = rbconn;
        }

        if (gc_count) {
                no_gc = true;
                tree_nodes_free(root, gc_nodes, gc_count);
                /* tree_node_free before new allocation permits
                 * allocator to re-use newly free'd object.
                 *
                 * This is a rare event; in most cases we will find
                 * existing node to re-use. (or gc_count is 0).
                 */
                goto restart;
        }

        /* no match, need to insert new node */
        rbconn = kmem_cache_alloc(connlimit_rb_cachep, GFP_ATOMIC);
        if (rbconn == NULL)
                return 0;

        conn = kmem_cache_alloc(connlimit_conn_cachep, GFP_ATOMIC);
        if (conn == NULL) {
                kmem_cache_free(connlimit_rb_cachep, rbconn);
                return 0;
        }

        conn->tuple = *tuple;
        conn->addr = *addr;
        rbconn->addr = *addr;

        INIT_HLIST_HEAD(&rbconn->hhead);
        hlist_add_head(&conn->node, &rbconn->hhead);

        rb_link_node(&rbconn->node, parent, rbnode);
        rb_insert_color(&rbconn->node, root);
        return 1;
}

static int count_them(struct net *net,
                      struct xt_connlimit_data *data,
                      const struct nf_conntrack_tuple *tuple,
                      const union nf_inet_addr *addr,
                      const union nf_inet_addr *mask,
                      u_int8_t family,
                      const struct nf_conntrack_zone *zone)
{
        struct rb_root *root;
        int count;
        u32 hash;

        if (family == NFPROTO_IPV6) {
                hash = connlimit_iphash6(addr, mask);
                root = &data->climit_root6[hash];
        } else {
                hash = connlimit_iphash(addr->ip & mask->ip);
                root = &data->climit_root4[hash];
        }

        spin_lock_bh(&xt_connlimit_locks[hash % CONNLIMIT_LOCK_SLOTS]);

        count = count_tree(net, root, tuple, addr, mask, family, zone);

        spin_unlock_bh(&xt_connlimit_locks[hash % CONNLIMIT_LOCK_SLOTS]);

        return count;
}

static bool
connlimit_mt(const struct sk_buff *skb, struct xt_action_param *par)
{
        struct net *net = par->net;
        const struct xt_connlimit_info *info = par->matchinfo;
        union nf_inet_addr addr;
        struct nf_conntrack_tuple tuple;
        const struct nf_conntrack_tuple *tuple_ptr = &tuple;
        const struct nf_conntrack_zone *zone = &nf_ct_zone_dflt;
        enum ip_conntrack_info ctinfo;
        const struct nf_conn *ct;
        unsigned int connections;

        ct = nf_ct_get(skb, &ctinfo);
        if (ct != NULL) {
                tuple_ptr = &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple;
                zone = nf_ct_zone(ct);
        } else if (!nf_ct_get_tuplepr(skb, skb_network_offset(skb),
                                      par->family, net, &tuple)) {
                goto hotdrop;
        }

        if (par->family == NFPROTO_IPV6) {
                const struct ipv6hdr *iph = ipv6_hdr(skb);
                memcpy(&addr.ip6, (info->flags & XT_CONNLIMIT_DADDR) ?
                       &iph->daddr : &iph->saddr, sizeof(addr.ip6));
        } else {
                const struct iphdr *iph = ip_hdr(skb);
                addr.ip = (info->flags & XT_CONNLIMIT_DADDR) ?
                          iph->daddr : iph->saddr;
        }

        connections = count_them(net, info->data, tuple_ptr, &addr,
                                 &info->mask, par->family, zone);
        if (connections == 0)
                /* kmalloc failed, drop it entirely */
                goto hotdrop;

        return (connections > info->limit) ^
               !!(info->flags & XT_CONNLIMIT_INVERT);

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

static int connlimit_mt_check(const struct xt_mtchk_param *par)
{
        struct xt_connlimit_info *info = par->matchinfo;
        unsigned int i;
        int ret;

        if (unlikely(!connlimit_rnd)) {
                u_int32_t rand;

                do {
                        get_random_bytes(&rand, sizeof(rand));
                } while (!rand);
                cmpxchg(&connlimit_rnd, 0, rand);
        }
        ret = nf_ct_l3proto_try_module_get(par->family);
        if (ret < 0) {
                pr_info("cannot load conntrack support for "
                        "address family %u\n", par->family);
                return ret;
        }

        /* init private data */
        info->data = kmalloc(sizeof(struct xt_connlimit_data), GFP_KERNEL);
        if (info->data == NULL) {
                nf_ct_l3proto_module_put(par->family);
                return -ENOMEM;
        }

        for (i = 0; i < ARRAY_SIZE(info->data->climit_root4); ++i)
                info->data->climit_root4[i] = RB_ROOT;
        for (i = 0; i < ARRAY_SIZE(info->data->climit_root6); ++i)
                info->data->climit_root6[i] = RB_ROOT;

        return 0;
}

static void destroy_tree(struct rb_root *r)
{
        struct xt_connlimit_conn *conn;
        struct xt_connlimit_rb *rbconn;
        struct hlist_node *n;
        struct rb_node *node;

        while ((node = rb_first(r)) != NULL) {
                rbconn = container_of(node, struct xt_connlimit_rb, node);

                rb_erase(node, r);

                hlist_for_each_entry_safe(conn, n, &rbconn->hhead, node)
                        kmem_cache_free(connlimit_conn_cachep, conn);

                kmem_cache_free(connlimit_rb_cachep, rbconn);
        }
}

static void connlimit_mt_destroy(const struct xt_mtdtor_param *par)
{
        const struct xt_connlimit_info *info = par->matchinfo;
        unsigned int i;

        nf_ct_l3proto_module_put(par->family);

        for (i = 0; i < ARRAY_SIZE(info->data->climit_root4); ++i)
                destroy_tree(&info->data->climit_root4[i]);
        for (i = 0; i < ARRAY_SIZE(info->data->climit_root6); ++i)
                destroy_tree(&info->data->climit_root6[i]);

        kfree(info->data);
}

static struct xt_match connlimit_mt_reg __read_mostly = {
        .name       = "connlimit",
        .revision   = 1,
        .family     = NFPROTO_UNSPEC,
        .checkentry = connlimit_mt_check,
        .match      = connlimit_mt,
        .matchsize  = sizeof(struct xt_connlimit_info),
        .destroy    = connlimit_mt_destroy,
        .me         = THIS_MODULE,
};

static int __init connlimit_mt_init(void)
{
        int ret, i;

        BUILD_BUG_ON(CONNLIMIT_LOCK_SLOTS > CONNLIMIT_SLOTS);
        BUILD_BUG_ON((CONNLIMIT_SLOTS % CONNLIMIT_LOCK_SLOTS) != 0);

        for (i = 0; i < CONNLIMIT_LOCK_SLOTS; ++i)
                spin_lock_init(&xt_connlimit_locks[i]);

        connlimit_conn_cachep = kmem_cache_create("xt_connlimit_conn",
                                           sizeof(struct xt_connlimit_conn),
                                           0, 0, NULL);
        if (!connlimit_conn_cachep)
                return -ENOMEM;

        connlimit_rb_cachep = kmem_cache_create("xt_connlimit_rb",
                                           sizeof(struct xt_connlimit_rb),
                                           0, 0, NULL);
        if (!connlimit_rb_cachep) {
                kmem_cache_destroy(connlimit_conn_cachep);
                return -ENOMEM;
        }
        ret = xt_register_match(&connlimit_mt_reg);
        if (ret != 0) {
                kmem_cache_destroy(connlimit_conn_cachep);
                kmem_cache_destroy(connlimit_rb_cachep);
        }
        return ret;
}

static void __exit connlimit_mt_exit(void)
{
        xt_unregister_match(&connlimit_mt_reg);
        kmem_cache_destroy(connlimit_conn_cachep);
        kmem_cache_destroy(connlimit_rb_cachep);
}

module_init(connlimit_mt_init);
module_exit(connlimit_mt_exit);
MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");
MODULE_DESCRIPTION("Xtables: Number of connections matching");
MODULE_LICENSE("GPL");
MODULE_ALIAS("ipt_connlimit");
MODULE_ALIAS("ip6t_connlimit");