/*
 * count the number of connections matching an arbitrary key.
 *
 * (C) 2017 Red Hat GmbH
 * Author: Florian Westphal <fw@strlen.de>
 *
 * split from xt_connlimit.c:
 *   (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
 */
#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 <net/netfilter/nf_conntrack.h>
#include <net/netfilter/nf_conntrack_count.h>
#include <net/netfilter/nf_conntrack_core.h>
#include <net/netfilter/nf_conntrack_tuple.h>
#include <net/netfilter/nf_conntrack_zones.h>

#define CONNCOUNT_SLOTS         256U

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

#define CONNCOUNT_GC_MAX_NODES  8
#define MAX_KEYLEN              5

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

struct nf_conncount_rb {
        struct rb_node node;
        struct hlist_head hhead; /* connections/hosts in same subnet */
        u32 key[MAX_KEYLEN];
};

static spinlock_t nf_conncount_locks[CONNCOUNT_LOCK_SLOTS] __cacheline_aligned_in_smp;

struct nf_conncount_data {
        unsigned int keylen;
        struct rb_root root[CONNCOUNT_SLOTS];
};

static u_int32_t conncount_rnd __read_mostly;
static struct kmem_cache *conncount_rb_cachep __read_mostly;
static struct kmem_cache *conncount_conn_cachep __read_mostly;

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 false;
}

static int key_diff(const u32 *a, const u32 *b, unsigned int klen)
{
        return memcmp(a, b, klen * sizeof(u32));
}

static bool add_hlist(struct hlist_head *head,
                      const struct nf_conntrack_tuple *tuple)
{
        struct nf_conncount_tuple *conn;

        conn = kmem_cache_alloc(conncount_conn_cachep, GFP_ATOMIC);
        if (conn == NULL)
                return false;
        conn->tuple = *tuple;
        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 nf_conncount_tuple *conn;
        struct hlist_node *n;
        struct nf_conn *found_ct;
        unsigned int length = 0;

        *addit = tuple ? true : false;

        /* 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(conncount_conn_cachep, conn);
                        continue;
                }

                found_ct = nf_ct_tuplehash_to_ctrack(found);

                if (tuple && 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(conncount_conn_cachep, conn);
                        continue;
                }

                nf_ct_put(found_ct);
                length++;
        }

        return length;
}

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

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

static unsigned int
count_tree(struct net *net, struct rb_root *root,
           const u32 *key, u8 keylen,
           const struct nf_conntrack_tuple *tuple,
           const struct nf_conntrack_zone *zone)
{
        struct nf_conncount_rb *gc_nodes[CONNCOUNT_GC_MAX_NODES];
        struct rb_node **rbnode, *parent;
        struct nf_conncount_rb *rbconn;
        struct nf_conncount_tuple *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 = rb_entry(*rbnode, struct nf_conncount_rb, node);

                parent = *rbnode;
                diff = key_diff(key, rbconn->key, keylen);
                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))
                                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;
        }

        if (!tuple)
                return 0;

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

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

        conn->tuple = *tuple;
        memcpy(rbconn->key, key, sizeof(u32) * keylen);

        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;
}

/* Count and return number of conntrack entries in 'net' with particular 'key'.
 * If 'tuple' is not null, insert it into the accounting data structure.
 */
unsigned int nf_conncount_count(struct net *net,
                                struct nf_conncount_data *data,
                                const u32 *key,
                                const struct nf_conntrack_tuple *tuple,
                                const struct nf_conntrack_zone *zone)
{
        struct rb_root *root;
        int count;
        u32 hash;

        hash = jhash2(key, data->keylen, conncount_rnd) % CONNCOUNT_SLOTS;
        root = &data->root[hash];

        spin_lock_bh(&nf_conncount_locks[hash % CONNCOUNT_LOCK_SLOTS]);

        count = count_tree(net, root, key, data->keylen, tuple, zone);

        spin_unlock_bh(&nf_conncount_locks[hash % CONNCOUNT_LOCK_SLOTS]);

        return count;
}
EXPORT_SYMBOL_GPL(nf_conncount_count);

struct nf_conncount_data *nf_conncount_init(struct net *net, unsigned int family,
                                            unsigned int keylen)
{
        struct nf_conncount_data *data;
        int ret, i;

        if (keylen % sizeof(u32) ||
            keylen / sizeof(u32) > MAX_KEYLEN ||
            keylen == 0)
                return ERR_PTR(-EINVAL);

        net_get_random_once(&conncount_rnd, sizeof(conncount_rnd));

        data = kmalloc(sizeof(*data), GFP_KERNEL);
        if (!data)
                return ERR_PTR(-ENOMEM);

        ret = nf_ct_netns_get(net, family);
        if (ret < 0) {
                kfree(data);
                return ERR_PTR(ret);
        }

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

        data->keylen = keylen / sizeof(u32);

        return data;
}
EXPORT_SYMBOL_GPL(nf_conncount_init);

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

        while ((node = rb_first(r)) != NULL) {
                rbconn = rb_entry(node, struct nf_conncount_rb, node);

                rb_erase(node, r);

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

                kmem_cache_free(conncount_rb_cachep, rbconn);
        }
}

void nf_conncount_destroy(struct net *net, unsigned int family,
                          struct nf_conncount_data *data)
{
        unsigned int i;

        nf_ct_netns_put(net, family);

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

        kfree(data);
}
EXPORT_SYMBOL_GPL(nf_conncount_destroy);

static int __init nf_conncount_modinit(void)
{
        int i;

        BUILD_BUG_ON(CONNCOUNT_LOCK_SLOTS > CONNCOUNT_SLOTS);
        BUILD_BUG_ON((CONNCOUNT_SLOTS % CONNCOUNT_LOCK_SLOTS) != 0);

        for (i = 0; i < CONNCOUNT_LOCK_SLOTS; ++i)
                spin_lock_init(&nf_conncount_locks[i]);

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

        conncount_rb_cachep = kmem_cache_create("nf_conncount_rb",
                                           sizeof(struct nf_conncount_rb),
                                           0, 0, NULL);
        if (!conncount_rb_cachep) {
                kmem_cache_destroy(conncount_conn_cachep);
                return -ENOMEM;
        }

        return 0;
}

static void __exit nf_conncount_modexit(void)
{
        kmem_cache_destroy(conncount_conn_cachep);
        kmem_cache_destroy(conncount_rb_cachep);
}

module_init(nf_conncount_modinit);
module_exit(nf_conncount_modexit);
MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");
MODULE_AUTHOR("Florian Westphal <fw@strlen.de>");
MODULE_DESCRIPTION("netfilter: count number of connections matching a key");
MODULE_LICENSE("GPL");