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From: Pablo Neira Ayuso <pablo@netfilter.org>
To: netfilter-devel@vger.kernel.org
Cc: davem@davemloft.net, netdev@vger.kernel.org
Subject: [PATCH 5/5] netfilter: nf_tables: Fix nft limit burst handling
Date: Thu, 24 Aug 2017 16:43:31 +0200
Message-ID: <1503585811-13447-6-git-send-email-pablo@netfilter.org> (raw)
In-Reply-To: <1503585811-13447-1-git-send-email-pablo@netfilter.org>

From: andy zhou <azhou@ovn.org>

Current implementation treats the burst configuration the same as
rate configuration. This can cause the per packet cost to be lower
than configured. In effect, this bug causes the token bucket to be
refilled at a higher rate than what user has specified.

This patch changes the implementation so that the token bucket size
is controlled by "rate + burst", while maintain the token bucket
refill rate the same as user specified.

Fixes: 96518518cc41 ("netfilter: add nftables")
Signed-off-by: Andy Zhou <azhou@ovn.org>
Acked-by: Joe Stringer <joe@ovn.org>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---
 net/netfilter/nft_limit.c | 25 ++++++++++++++-----------
 1 file changed, 14 insertions(+), 11 deletions(-)

diff --git a/net/netfilter/nft_limit.c b/net/netfilter/nft_limit.c
index 18dd57a52651..14538b1d4d11 100644
--- a/net/netfilter/nft_limit.c
+++ b/net/netfilter/nft_limit.c
@@ -65,19 +65,23 @@ static int nft_limit_init(struct nft_limit *limit,
 	limit->nsecs = unit * NSEC_PER_SEC;
 	if (limit->rate == 0 || limit->nsecs < unit)
 		return -EOVERFLOW;
-	limit->tokens = limit->tokens_max = limit->nsecs;
-
-	if (tb[NFTA_LIMIT_BURST]) {
-		u64 rate;
 
+	if (tb[NFTA_LIMIT_BURST])
 		limit->burst = ntohl(nla_get_be32(tb[NFTA_LIMIT_BURST]));
+	else
+		limit->burst = 0;
+
+	if (limit->rate + limit->burst < limit->rate)
+		return -EOVERFLOW;
 
-		rate = limit->rate + limit->burst;
-		if (rate < limit->rate)
-			return -EOVERFLOW;
+	/* The token bucket size limits the number of tokens can be
+	 * accumulated. tokens_max specifies the bucket size.
+	 * tokens_max = unit * (rate + burst) / rate.
+	 */
+	limit->tokens = div_u64(limit->nsecs * (limit->rate + limit->burst),
+				limit->rate);
+	limit->tokens_max = limit->tokens;
 
-		limit->rate = rate;
-	}
 	if (tb[NFTA_LIMIT_FLAGS]) {
 		u32 flags = ntohl(nla_get_be32(tb[NFTA_LIMIT_FLAGS]));
 
@@ -95,9 +99,8 @@ static int nft_limit_dump(struct sk_buff *skb, const struct nft_limit *limit,
 {
 	u32 flags = limit->invert ? NFT_LIMIT_F_INV : 0;
 	u64 secs = div_u64(limit->nsecs, NSEC_PER_SEC);
-	u64 rate = limit->rate - limit->burst;
 
-	if (nla_put_be64(skb, NFTA_LIMIT_RATE, cpu_to_be64(rate),
+	if (nla_put_be64(skb, NFTA_LIMIT_RATE, cpu_to_be64(limit->rate),
 			 NFTA_LIMIT_PAD) ||
 	    nla_put_be64(skb, NFTA_LIMIT_UNIT, cpu_to_be64(secs),
 			 NFTA_LIMIT_PAD) ||
-- 
2.1.4

  parent reply index

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-08-24 14:43 [PATCH 0/5] Netfilter fixes for net Pablo Neira Ayuso
2017-08-24 14:43 ` [PATCH 1/5] netfilter: ipt_CLUSTERIP: fix use-after-free of proc entry Pablo Neira Ayuso
2017-08-24 14:43 ` [PATCH 2/5] netfilter: nft_compat: check extension hook mask only if set Pablo Neira Ayuso
2017-08-24 14:43 ` [PATCH 3/5] netfilter: x_tables: Fix use-after-free in ipt_do_table Pablo Neira Ayuso
2017-08-24 14:43 ` [PATCH 4/5] netfilter: check for seqadj ext existence before adding it in nf_nat_setup_info Pablo Neira Ayuso
2017-08-24 14:43 ` Pablo Neira Ayuso [this message]
2017-08-24 18:49 ` [PATCH 0/5] Netfilter fixes for net David Miller

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