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>

/* 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 {
	u16	bitmap_size;
	u8	bitmap[];
};

static inline void nft_bitmap_location(u32 key, u32 *idx, u32 *off)
{
	u32 k = (key << 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(*key, &idx, &off);

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

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_set_ext *ext = elem->priv;
	u8 genmask = nft_genmask_next(net);
	u32 idx, off;

	nft_bitmap_location(nft_set_ext_key(ext)->data[0], &idx, &off);
	if (nft_bitmap_active(priv->bitmap, idx, off, genmask))
		return -EEXIST;

	/* Enter 01 state. */
	priv->bitmap[idx] |= (genmask << off);

	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_set_ext *ext = elem->priv;
	u8 genmask = nft_genmask_next(net);
	u32 idx, off;

	nft_bitmap_location(nft_set_ext_key(ext)->data[0], &idx, &off);
	/* Enter 00 state. */
	priv->bitmap[idx] &= ~(genmask << off);
}

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_set_ext *ext = elem->priv;
	u8 genmask = nft_genmask_next(net);
	u32 idx, off;

	nft_bitmap_location(nft_set_ext_key(ext)->data[0], &idx, &off);
	/* Enter 11 state. */
	priv->bitmap[idx] |= (genmask << off);
}

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

	nft_bitmap_location(nft_set_ext_key(ext)->data[0], &idx, &off);
	/* Enter 10 state, similar to deactivation. */
	priv->bitmap[idx] &= ~(genmask << off);

	return true;
}

static struct nft_set_ext *nft_bitmap_ext_alloc(const struct nft_set *set,
						const struct nft_set_elem *elem)
{
	struct nft_set_ext_tmpl tmpl;
	struct nft_set_ext *ext;

	nft_set_ext_prepare(&tmpl);
	nft_set_ext_add_length(&tmpl, NFT_SET_EXT_KEY, set->klen);

	ext = kzalloc(tmpl.len, GFP_KERNEL);
	if (!ext)
		return NULL;

	nft_set_ext_init(ext, &tmpl);
	memcpy(nft_set_ext_key(ext), elem->key.val.data, set->klen);

	return ext;
}

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);
	u8 genmask = nft_genmask_next(net);
	struct nft_set_ext *ext;
	u32 idx, off, key = 0;

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

	if (!nft_bitmap_active(priv->bitmap, idx, off, genmask))
		return NULL;

	/* We have no real set extension since this is a bitmap, allocate this
	 * dummy object that is released from the commit/abort path.
	 */
	ext = nft_bitmap_ext_alloc(set, elem);
	if (!ext)
		return NULL;

	/* Enter 10 state. */
	priv->bitmap[idx] &= ~(genmask << off);

	return ext;
}

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_set_ext_tmpl tmpl;
	struct nft_set_elem elem;
	struct nft_set_ext *ext;
	int idx, off;
	u16 key;

	nft_set_ext_prepare(&tmpl);
	nft_set_ext_add_length(&tmpl, NFT_SET_EXT_KEY, set->klen);

	for (idx = 0; idx < priv->bitmap_size; idx++) {
		for (off = 0; off < BITS_PER_BYTE; off += 2) {
			if (iter->count < iter->skip)
				goto cont;

			if (!nft_bitmap_active(priv->bitmap, idx, off,
					       iter->genmask))
				goto cont;

			ext = kzalloc(tmpl.len, GFP_KERNEL);
			if (!ext) {
				iter->err = -ENOMEM;
				return;
			}
			nft_set_ext_init(ext, &tmpl);
			key = ((idx * BITS_PER_BYTE) + off) >> 1;
			memcpy(nft_set_ext_key(ext), &key, set->klen);

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

			/* On set flush, this dummy extension object is released
			 * from the commit/abort path.
			 */
			if (!iter->flush)
				kfree(ext);

			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[])
{
	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);

	priv->bitmap_size = nft_bitmap_size(set->klen);

	return 0;
}

static void nft_bitmap_destroy(const struct nft_set *set)
{
}

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_ops nft_bitmap_ops __read_mostly = {
	.privsize	= nft_bitmap_privsize,
	.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,
	.owner		= THIS_MODULE,
};

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

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

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();