net/netfilter/nft_set_bitmap.c

/*
 * 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);

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

static unsigned int 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;
}

static struct nft_set_type nft_bitmap_type;
static struct nft_set_ops nft_bitmap_ops __read_mostly = {
	.type		= &nft_bitmap_type,
	.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,
};

static struct nft_set_type nft_bitmap_type __read_mostly = {
	.ops		= &nft_bitmap_ops,
	.owner		= THIS_MODULE,
};

static int __init nft_bitmap_module_init(void)
{
	return nft_register_set(&nft_bitmap_type);
}

static void __exit nft_bitmap_module_exit(void)
{
	nft_unregister_set(&nft_bitmap_type);
}

module_init(nft_bitmap_module_init);
module_exit(nft_bitmap_module_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Pablo Neira Ayuso <pablo@netfilter.org>");
MODULE_ALIAS_NFT_SET();