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: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/net/netfilter/nft_limit.c b/net/netfilter/nft_limit.c
index d0788e1..c79703e 100644 (file)
--- a/net/netfilter/nft_limit.c
+++ b/net/netfilter/nft_limit.c
@@ -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;
+       priv->rate = be64_to_cpu(nla_get_be64(tb[NFTA_LIMIT_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;