Commit c26844ed authored by andy zhou's avatar andy zhou Committed by Pablo Neira Ayuso
Browse files

netfilter: nf_tables: Fix nft limit burst handling 



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: 96518518 ("netfilter: add nftables")
Signed-off-by: default avatarAndy Zhou <azhou@ovn.org>
Acked-by: default avatarJoe Stringer <joe@ovn.org>
Signed-off-by: default avatarPablo Neira Ayuso <pablo@netfilter.org>
parent ab6dd1be

net/netfilter/nft_limit.c

+14 −11
Original line number Diff line number Diff line
@@ -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;



		rate = limit->rate + limit->burst;

		if (rate < limit->rate)

	if (limit->rate + limit->burst < limit->rate)

		return -EOVERFLOW;



		limit->rate = rate;

	}

	/* 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;



	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) ||

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