On Thu, 16 Nov 2000, Dan Aloni wrote:
> On Wed, 15 Nov 2000, Guus Sliepen wrote:
>
> > > I was DDoS'd today while away and came home to find the firewall unable to
> > > do anything network related (although my connection to irc was still
> > > working oddly). a quick dmesg showed the problem.
> > > ip_conntrack: maximum limit of 2048 entries exceeded
> > [...]
> >
> > I have also seen this happen on a box which ran test9. Apparently because of
> > it's long uptime, because the logs should no signs of an attack.
> >
> > I guess conntrack forgets to flush some entries? Or maybe there is no way it can
> > recover from a full conntrack table? Is it maybe necessary to make the maximum
> > size a configurable option? Or a userspace conntrack daemon like the arpd?
>
> >From reading the sources I got the impression that the use count of
> the ip_conntrack struct isn't decremented properly. This causes
> destroy_conntrack() not to free ip_conntrack's - which results allocation
> until the maximum (ip_conntrack_max), and failing to allocate new ones.
I think I got something, icmp_error_track() increases the use count
(calling ip_conntrack_find_get()) when it returns with no error (not NULL).
Whoever calls icmp_error_track() and gets a valid pointer to ip_conntrack,
must call ip_conntrack_put() - look at ip_conntrack_in(), line 685, the
pointer is just used in a boolean expression without calling
ip_conntrack_put(). I'm not sure if other places needed fixing, but anyway
try this patch:
--- linux-2.4.0-test11-pre5/net/ipv4/netfilter/ip_conntrack_core.c Tue Nov 14
09:56:16 2000
+++ linux/net/ipv4/netfilter/ip_conntrack_core.c Thu Nov 16 01:35:13 2000
@@ -682,8 +682,10 @@
/* It may be an icmp error... */
if ((*pskb)->nh.iph->protocol == IPPROTO_ICMP
- && icmp_error_track(*pskb, &ctinfo, hooknum))
+ && (ct = icmp_error_track(*pskb, &ctinfo, hooknum))) {
+ ip_conntrack_put(ct);
return NF_ACCEPT;
+ }
if (!(ct = resolve_normal_ct(*pskb, proto,&set_reply,hooknum,&ctinfo)))
/* Not valid part of a connection */
--
Dan Aloni
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