Subject: Re: deleting a conntrack record

From: Patrick McHardy <[email-masked]>
Date: Thu, 17 Jun 2004 18:42:35 +0200

Tobias DiPasquale wrote:
> On Thu, 17 Jun 2004 18:02:16 +0200, Patrick McHardy <[email-masked]> wrote:
> 
>>The function passed to ip_ct_selective_cleanup is supposed to decide
>>if a conntrack should be destroyed by returning 0/1, not to do it
>>itself. ip_ct_selective_cleanup tries to destroy the already destroyed
>>conntrack.
> 
> This results in a memory leak in the conntrack slab cache. If you
> don't call ip_conntrack_put(), the conntrack entry leaves the
> ip_ct_selective_cleanup() function with a value >0 and thus is a
> permanent part of the scenery in RAM. As well, its been removed from
> the conntrack hash table, so it no longer appears in
> /proc/net/ip_conntrack, but you can see the effects by viewing
> /proc/slabinfo.

Now I remember - the reason why ctnetlink called ip_conntrack_put
in ctnetlink_kill is because it uses ip_conntrack_find_get before,
which increments the reference count. This is wrong because the
conntrack is then destroyed immediately after returning 1 to
ip_ct_selective_cleanup, but still used for comparing the tuple.
You (and ctnetlink) need to call ip_conntrack_put after the
call to ip_ct_selective_cleanup. In fact you shouldn't use
ip_ct_selective_cleanup at all but destroy it yourself. You
already have a reference, so there is no need to iterate through
the entire hash.

Regards
Patrick