/*
 * Copyright (c) 2017 Pablo Neira Ayuso <pablo@netfilter.org>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */

#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/list.h>
#include <linux/netlink.h>
#include <linux/netfilter.h>
#include <linux/netfilter/nf_tables.h>
#include <net/netfilter/nf_tables.h>

struct nft_bitmap_elem {
        struct list_head        head;
        struct nft_set_ext      ext;
};

/* This bitmap uses two bits to represent one element. These two bits determine
 * the element state in the current and the future generation.
 *
 * An element can be in three states. The generation cursor is represented using
 * the ^ character, note that this cursor shifts on every succesful transaction.
 * If no transaction is going on, we observe all elements are in the following
 * state:
 *
 * 11 = this element is active in the current generation. In case of no updates,
 * ^    it stays active in the next generation.
 * 00 = this element is inactive in the current generation. In case of no
 * ^    updates, it stays inactive in the next generation.
 *
 * On transaction handling, we observe these two temporary states:
 *
 * 01 = this element is inactive in the current generation and it becomes active
 * ^    in the next one. This happens when the element is inserted but commit
 *      path has not yet been executed yet, so activation is still pending. On
 *      transaction abortion, the element is removed.
 * 10 = this element is active in the current generation and it becomes inactive
 * ^    in the next one. This happens when the element is deactivated but commit
 *      path has not yet been executed yet, so removal is still pending. On
 *      transation abortion, the next generation bit is reset to go back to
 *      restore its previous state.
 */
struct nft_bitmap {
        struct  list_head       list;
        u16                     bitmap_size;
        u8                      bitmap[];
};

static inline void nft_bitmap_location(const struct nft_set *set,
                                       const void *key,
                                       u32 *idx, u32 *off)
{
        u32 k;

        if (set->klen == 2)
                k = *(u16 *)key;
        else
                k = *(u8 *)key;
        k <<= 1;

        *idx = k / BITS_PER_BYTE;
        *off = k % BITS_PER_BYTE;
}

/* Fetch the two bits that represent the element and check if it is active based
 * on the generation mask.
 */
static inline bool
nft_bitmap_active(const u8 *bitmap, u32 idx, u32 off, u8 genmask)
{
        return (bitmap[idx] & (0x3 << off)) & (genmask << off);
}

static bool nft_bitmap_lookup(const struct net *net, const struct nft_set *set,
                              const u32 *key, const struct nft_set_ext **ext)
{
        const struct nft_bitmap *priv = nft_set_priv(set);
        u8 genmask = nft_genmask_cur(net);
        u32 idx, off;

        nft_bitmap_location(set, key, &idx, &off);
        *ext = NULL;

        return nft_bitmap_active(priv->bitmap, idx, off, genmask);
}

static struct nft_bitmap_elem *
nft_bitmap_elem_find(const struct nft_set *set, struct nft_bitmap_elem *this,
                     u8 genmask)
{
        const struct nft_bitmap *priv = nft_set_priv(set);
        struct nft_bitmap_elem *be;

        list_for_each_entry_rcu(be, &priv->list, head) {
                if (memcmp(nft_set_ext_key(&be->ext),
                           nft_set_ext_key(&this->ext), set->klen) ||
                    !nft_set_elem_active(&be->ext, genmask))
                        continue;

                return be;
        }
        return NULL;
}

static void *nft_bitmap_get(const struct net *net, const struct nft_set *set,
                            const struct nft_set_elem *elem, unsigned int flags)
{
        const struct nft_bitmap *priv = nft_set_priv(set);
        u8 genmask = nft_genmask_cur(net);
        struct nft_bitmap_elem *be;

        list_for_each_entry_rcu(be, &priv->list, head) {
                if (memcmp(nft_set_ext_key(&be->ext), elem->key.val.data, set->klen) ||
                    !nft_set_elem_active(&be->ext, genmask))
                        continue;

                return be;
        }
        return ERR_PTR(-ENOENT);
}

static int nft_bitmap_insert(const struct net *net, const struct nft_set *set,
                             const struct nft_set_elem *elem,
                             struct nft_set_ext **ext)
{
        struct nft_bitmap *priv = nft_set_priv(set);
        struct nft_bitmap_elem *new = elem->priv, *be;
        u8 genmask = nft_genmask_next(net);
        u32 idx, off;

        be = nft_bitmap_elem_find(set, new, genmask);
        if (be) {
                *ext = &be->ext;
                return -EEXIST;
        }

        nft_bitmap_location(set, nft_set_ext_key(&new->ext), &idx, &off);
        /* Enter 01 state. */
        priv->bitmap[idx] |= (genmask << off);
        list_add_tail_rcu(&new->head, &priv->list);

        return 0;
}

static void nft_bitmap_remove(const struct net *net,
                              const struct nft_set *set,
                              const struct nft_set_elem *elem)
{
        struct nft_bitmap *priv = nft_set_priv(set);
        struct nft_bitmap_elem *be = elem->priv;
        u8 genmask = nft_genmask_next(net);
        u32 idx, off;

        nft_bitmap_location(set, nft_set_ext_key(&be->ext), &idx, &off);
        /* Enter 00 state. */
        priv->bitmap[idx] &= ~(genmask << off);
        list_del_rcu(&be->head);
}

static void nft_bitmap_activate(const struct net *net,
                                const struct nft_set *set,
                                const struct nft_set_elem *elem)
{
        struct nft_bitmap *priv = nft_set_priv(set);
        struct nft_bitmap_elem *be = elem->priv;
        u8 genmask = nft_genmask_next(net);
        u32 idx, off;

        nft_bitmap_location(set, nft_set_ext_key(&be->ext), &idx, &off);
        /* Enter 11 state. */
        priv->bitmap[idx] |= (genmask << off);
        nft_set_elem_change_active(net, set, &be->ext);
}

static bool nft_bitmap_flush(const struct net *net,
                             const struct nft_set *set, void *_be)
{
        struct nft_bitmap *priv = nft_set_priv(set);
        u8 genmask = nft_genmask_next(net);
        struct nft_bitmap_elem *be = _be;
        u32 idx, off;

        nft_bitmap_location(set, nft_set_ext_key(&be->ext), &idx, &off);
        /* Enter 10 state, similar to deactivation. */
        priv->bitmap[idx] &= ~(genmask << off);
        nft_set_elem_change_active(net, set, &be->ext);

        return true;
}

static void *nft_bitmap_deactivate(const struct net *net,
                                   const struct nft_set *set,
                                   const struct nft_set_elem *elem)
{
        struct nft_bitmap *priv = nft_set_priv(set);
        struct nft_bitmap_elem *this = elem->priv, *be;
        u8 genmask = nft_genmask_next(net);
        u32 idx, off;

        nft_bitmap_location(set, elem->key.val.data, &idx, &off);

        be = nft_bitmap_elem_find(set, this, genmask);
        if (!be)
                return NULL;

        /* Enter 10 state. */
        priv->bitmap[idx] &= ~(genmask << off);
        nft_set_elem_change_active(net, set, &be->ext);

        return be;
}

static void nft_bitmap_walk(const struct nft_ctx *ctx,
                            struct nft_set *set,
                            struct nft_set_iter *iter)
{
        const struct nft_bitmap *priv = nft_set_priv(set);
        struct nft_bitmap_elem *be;
        struct nft_set_elem elem;

        list_for_each_entry_rcu(be, &priv->list, head) {
                if (iter->count < iter->skip)
                        goto cont;
                if (!nft_set_elem_active(&be->ext, iter->genmask))
                        goto cont;

                elem.priv = be;

                iter->err = iter->fn(ctx, set, iter, &elem);

                if (iter->err < 0)
                        return;
cont:
                iter->count++;
        }
}

/* The bitmap size is pow(2, key length in bits) / bits per byte. This is
 * multiplied by two since each element takes two bits. For 8 bit keys, the
 * bitmap consumes 66 bytes. For 16 bit keys, 16388 bytes.
 */
static inline u32 nft_bitmap_size(u32 klen)
{
        return ((2 << ((klen * BITS_PER_BYTE) - 1)) / BITS_PER_BYTE) << 1;
}

static inline u64 nft_bitmap_total_size(u32 klen)
{
        return sizeof(struct nft_bitmap) + nft_bitmap_size(klen);
}

static u64 nft_bitmap_privsize(const struct nlattr * const nla[],
                               const struct nft_set_desc *desc)
{
        u32 klen = ntohl(nla_get_be32(nla[NFTA_SET_KEY_LEN]));

        return nft_bitmap_total_size(klen);
}

static int nft_bitmap_init(const struct nft_set *set,
                           const struct nft_set_desc *desc,
                           const struct nlattr * const nla[])
{
        struct nft_bitmap *priv = nft_set_priv(set);

        INIT_LIST_HEAD(&priv->list);
        priv->bitmap_size = nft_bitmap_size(set->klen);

        return 0;
}

static void nft_bitmap_destroy(const struct nft_set *set)
{
        struct nft_bitmap *priv = nft_set_priv(set);
        struct nft_bitmap_elem *be, *n;

        list_for_each_entry_safe(be, n, &priv->list, head)
                nft_set_elem_destroy(set, be, true);
}

static bool nft_bitmap_estimate(const struct nft_set_desc *desc, u32 features,
                                struct nft_set_estimate *est)
{
        /* Make sure bitmaps we don't get bitmaps larger than 16 Kbytes. */
        if (desc->klen > 2)
                return false;

        est->size   = nft_bitmap_total_size(desc->klen);
        est->lookup = NFT_SET_CLASS_O_1;
        est->space  = NFT_SET_CLASS_O_1;

        return true;
}

struct nft_set_type nft_set_bitmap_type __read_mostly = {
        .owner          = THIS_MODULE,
        .ops            = {
                .privsize       = nft_bitmap_privsize,
                .elemsize       = offsetof(struct nft_bitmap_elem, ext),
                .estimate       = nft_bitmap_estimate,
                .init           = nft_bitmap_init,
                .destroy        = nft_bitmap_destroy,
                .insert         = nft_bitmap_insert,
                .remove         = nft_bitmap_remove,
                .deactivate     = nft_bitmap_deactivate,
                .flush          = nft_bitmap_flush,
                .activate       = nft_bitmap_activate,
                .lookup         = nft_bitmap_lookup,
                .walk           = nft_bitmap_walk,
                .get            = nft_bitmap_get,
        },
};