Commit dba27ec1 authored by Pablo Neira Ayuso's avatar Pablo Neira Ayuso
Browse files

netfilter: nft_limit: convert to token-based limiting at nanosecond granularity 



Rework the limit expression to use a token-based limiting approach that refills
the bucket gradually. The tokens are calculated at nanosecond granularity
instead jiffies to improve precision.

Signed-off-by: default avatarPablo Neira Ayuso <pablo@netfilter.org>
parent 09e4e42a

net/netfilter/nft_limit.c

+26 −16
Original line number Diff line number Diff line
@@ -20,10 +20,11 @@ 
static DEFINE_SPINLOCK(limit_lock);



struct nft_limit {

	u64		last;

	u64		tokens;

	u64		tokens_max;

	u64		rate;

	u64		unit;

	unsigned long	stamp;

	u64		nsecs;

};



static void nft_limit_pkts_eval(const struct nft_expr *expr,
@@ -31,18 +32,23 @@ static void nft_limit_pkts_eval(const struct nft_expr *expr, 
				const struct nft_pktinfo *pkt)

{

	struct nft_limit *priv = nft_expr_priv(expr);

	u64 now, tokens, cost = div_u64(priv->nsecs, priv->rate);

	s64 delta;



	spin_lock_bh(&limit_lock);

	if (time_after_eq(jiffies, priv->stamp)) {

		priv->tokens = priv->rate;

		priv->stamp = jiffies + priv->unit * HZ;

	}



	if (priv->tokens >= 1) {

		priv->tokens--;

	now = ktime_get_ns();

	tokens = priv->tokens + now - priv->last;

	if (tokens > priv->tokens_max)

		tokens = priv->tokens_max;



	priv->last = now;

	delta = tokens - cost;

	if (delta >= 0) {

		priv->tokens = delta;

		spin_unlock_bh(&limit_lock);

		return;

	}

	priv->tokens = tokens;

	spin_unlock_bh(&limit_lock);



	regs->verdict.code = NFT_BREAK;
@@ -58,25 +64,29 @@ static int nft_limit_init(const struct nft_ctx *ctx, 
			  const struct nlattr * const tb[])

{

	struct nft_limit *priv = nft_expr_priv(expr);

	u64 unit;



	if (tb[NFTA_LIMIT_RATE] == NULL ||

	    tb[NFTA_LIMIT_UNIT] == NULL)

		return -EINVAL;



	priv->rate = be64_to_cpu(nla_get_be64(tb[NFTA_LIMIT_RATE]));

	priv->unit   = be64_to_cpu(nla_get_be64(tb[NFTA_LIMIT_UNIT]));

	priv->stamp  = jiffies + priv->unit * HZ;

	priv->tokens = priv->rate;

	unit = be64_to_cpu(nla_get_be64(tb[NFTA_LIMIT_UNIT]));

	priv->nsecs = unit * NSEC_PER_SEC;

	if (priv->rate == 0 || priv->nsecs < unit)

		return -EOVERFLOW;

	priv->tokens = priv->tokens_max = priv->nsecs;

	priv->last = ktime_get_ns();

	return 0;

}



static int nft_limit_dump(struct sk_buff *skb, const struct nft_expr *expr)

{

	const struct nft_limit *priv = nft_expr_priv(expr);

	u64 secs = div_u64(priv->nsecs, NSEC_PER_SEC);



	if (nla_put_be64(skb, NFTA_LIMIT_RATE, cpu_to_be64(priv->rate)))

		goto nla_put_failure;

	if (nla_put_be64(skb, NFTA_LIMIT_UNIT, cpu_to_be64(priv->unit)))

	if (nla_put_be64(skb, NFTA_LIMIT_RATE, cpu_to_be64(priv->rate)) ||

	    nla_put_be64(skb, NFTA_LIMIT_UNIT, cpu_to_be64(secs)))

		goto nla_put_failure;

	return 0;