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SubjectRe: [PATCH] netfilter: conntrack: fix calculation of next bucket number in early_drop
On Wed, Oct 24, 2018 at 9:52 PM, Dmitry Safonov <dima@arista.com> wrote:
> 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>

Oops, found a bug in it - 'bucket' should be moved outside of the
loop. I'll send v2 tomorrow morning.

>
>> ---
>> 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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