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netfilter: nf_tables: Fix nft limit burst handling

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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: 96518518cc ("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>
This commit is contained in:
andy zhou 2017-08-21 12:38:53 -07:00 committed by Pablo Neira Ayuso
parent ab6dd1beac
commit c26844eda9
1 changed files with 14 additions and 11 deletions
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25
net/netfilter/nft_limit.c
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@ -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)
return -EOVERFLOW;
if (limit->rate + limit->burst < 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) ||