netdev - Re: [PATCH] inetpeer: ensure to set the maximum tokens the first time

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Date:	Thu, 27 Sep 2012 15:21:55 +0200
From:	Nicolas Dichtel <nicolas.dichtel@...nd.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	netdev@...r.kernel.org, davem@...emloft.net
Subject: Re: [PATCH] inetpeer: ensure to set the maximum tokens the first
 time

Le 27/09/2012 14:53, Eric Dumazet a écrit :
> On Thu, 2012-09-27 at 14:33 +0200, Nicolas Dichtel wrote:
>> When jiffies wraps around (for example, 5 minutes after the boot, see
>> INITIAL_JIFFIES) and peer has just been created, now - peer->rate_last can be
>> < XRLIM_BURST_FACTOR * timeout, so token is not set to the maximum value, thus
>> some icmp packets can be unexpectedly dropped.
>>
>> With this patch, it's still possible that last_rate and rate_tokens are 0 at the
>> same time after jiffies wraps round, but the probability is very low and the
>> only consequence is to let some ICMP packets bypass the filter.
>>
>> Signed-off-by: Nicolas Dichtel <nicolas.dichtel@...nd.com>
>> ---
>>   net/ipv4/inetpeer.c | 10 +++++++---
>>   1 file changed, 7 insertions(+), 3 deletions(-)
>>
>> diff --git a/net/ipv4/inetpeer.c b/net/ipv4/inetpeer.c
>> index e1e0a4e..92fec02 100644
>> --- a/net/ipv4/inetpeer.c
>> +++ b/net/ipv4/inetpeer.c
>> @@ -559,10 +559,14 @@ bool inet_peer_xrlim_allow(struct inet_peer *peer, int timeout)
>>
>>   	token = peer->rate_tokens;
>>   	now = jiffies;
>> -	token += now - peer->rate_last;
>> -	peer->rate_last = now;
>> -	if (token > XRLIM_BURST_FACTOR * timeout)
>> +	if (!peer->rate_last && !token)
>>   		token = XRLIM_BURST_FACTOR * timeout;
>> +	else {
>> +		token += now - peer->rate_last;
>> +		if (token > XRLIM_BURST_FACTOR * timeout)
>> +			token = XRLIM_BURST_FACTOR * timeout;
>> +	}
>> +	peer->rate_last = now;
>>   	if (token >= timeout) {
>>   		token -= timeout;
>>   		rc = true;
>
>
> I am sorry I dont understand your patch at all.
>
> Why not init rate_last to a more sensible value ?
>
> diff --git a/net/ipv4/inetpeer.c b/net/ipv4/inetpeer.c
> index e1e0a4e..25ed555 100644
> --- a/net/ipv4/inetpeer.c
> +++ b/net/ipv4/inetpeer.c
> @@ -510,7 +510,7 @@ relookup:
>   					secure_ipv6_id(daddr->addr.a6));
>   		p->metrics[RTAX_LOCK-1] = INETPEER_METRICS_NEW;
>   		p->rate_tokens = 0;
> -		p->rate_last = 0;
> +		p->rate_last = jiffies;
inet_getpeer(...,1) is called just before inet_peer_xrlim_allow().
So the result in inet_peer_xrlim_allow():
    	token = peer->rate_tokens; => 0
    	now = jiffies;
	token += now - peer->rate_last; => token += jiffies - jiffies => 0
So we have no token and packet is dropped.

Am I wrong?
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