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

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Date:	Thu, 27 Sep 2012 15:30:00 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	nicolas.dichtel@...nd.com
Cc:	netdev@...r.kernel.org, davem@...emloft.net
Subject: Re: [PATCH] inetpeer: ensure to set the maximum tokens the first
 time

On Thu, 2012-09-27 at 15:21 +0200, Nicolas Dichtel wrote:
> 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?

So find the right initializer ?

p->rate_last = jiffies;
p->rate_tokens = TOKENS_INIT;



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