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SubjectRe: [PATCH] netfilter: conntrack: fix calculation of next bucket number in early_drop
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On 10/25/18 4:48 AM, Vasily Khoruzhick wrote:
> If there's no entry to drop in bucket that corresponds to the hash,
> early_drop() should look for it in other buckets. But since it increments
> hash instead of bucket number, it actually looks in the same bucket 8
> times: hsize is 16k by default (14 bits) and hash is 32-bit value, so
> reciprocal_scale(hash, hsize) returns the same value for hash..hash+7 in
> most cases.
>
> Fix it by increasing bucket number instead of hash and rename _hash
> to bucket to avoid future confusion.
>
> Fixes: 3e86638e9a0b ("netfilter: conntrack: consider ct netns in early_drop logic")
> Cc: <stable@vger.kernel.org> # v4.7+
> Signed-off-by: Vasily Khoruzhick <vasilykh@arista.com>

Nice work!

Reviewed-by: Dmitry Safonov <dima@arista.com>

> ---
> net/netfilter/nf_conntrack_core.c | 11 +++++++----
> 1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
> index ca1168d67fac..a04af246b184 100644
> --- a/net/netfilter/nf_conntrack_core.c
> +++ b/net/netfilter/nf_conntrack_core.c
> @@ -1073,19 +1073,22 @@ static unsigned int early_drop_list(struct net *net,
> return drops;
> }
>
> -static noinline int early_drop(struct net *net, unsigned int _hash)
> +static noinline int early_drop(struct net *net, unsigned int hash)
> {
> unsigned int i;
>
> for (i = 0; i < NF_CT_EVICTION_RANGE; i++) {
> struct hlist_nulls_head *ct_hash;
> - unsigned int hash, hsize, drops;
> + unsigned int bucket, hsize, drops;
>
> rcu_read_lock();
> nf_conntrack_get_ht(&ct_hash, &hsize);
> - hash = reciprocal_scale(_hash++, hsize);
> + if (!i)
> + bucket = reciprocal_scale(hash, hsize);
> + else
> + bucket = (bucket + 1) % hsize;
>
> - drops = early_drop_list(net, &ct_hash[hash]);
> + drops = early_drop_list(net, &ct_hash[bucket]);
> rcu_read_unlock();
>
> if (drops) {
>

--
Dima

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