[LARTC] Re: IMQ device problems with iptables: dead looping?

[LARTC] Re: IMQ device problems with iptables: dead looping?

[Patrick McHardy]

Andrew Hall wrote:

>Hello,
>
>I am using the IMQ with iptables (latest versions) and asking all packets to
>be enqueued to IMQ0 from both prerouting and postrouting (using different
>iptables rules to mark different streams). When I do this I get the kernel
>saying:
>
>"Dead loop on netdevice imq0, fix it urgently!" and communications stop
>intermittently. If I remove the jump from either preroute or postroute it
>works fine but won't work together.
>
>Is this what is mean't to happen, because as far as I can see there is no
>loop happening here?
>

You probably forward packets. The loop happening ist
input-device -> prerouting -> imq (xmit_lock locked) -> reinject -> ... 
-> postrouting -> imq (LOCKED!!)

To avoid this one has to drop xmit_lock in imq_xmit function before 
reinjecteing and grab it back afterwards.
unfortunately this allows for endless recursion which is not possible in 
the kernel due to limited stack space.
I've completed a version which should hopefully fix this as many people 
requested such a feature.
I haven't released it yet because i have to do alot for my university 
atm and haven't got the time for testing
although i promised the new version to some people for january ;(
In about two weeks my semester-vacation start, i hope to release the new 
version very quickly afterwards.

Thanks for your patience,
Patrick

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[LARTC] Re: IMQ device problems with iptables: dead looping?

[Andrew Hall]

Hi Patrick,

Just wondering if you've had a chance to get your new version of the IMQ
device completed as yet to fix this deadlooping problem?

thanks and regards,

Andrew.
----- Original Message -----
From: "Patrick McHardy" <kaber@trash.net>
To: "Andrew Hall" <temp02@bluereef.com.au>
Cc: <lartc@mailman.ds9a.nl>
Sent: Wednesday, February 19, 2003 9:43 PM
Subject: Re: IMQ device problems with iptables: dead looping?


> Andrew Hall wrote:
>
> >Hello,
> >
> >I am using the IMQ with iptables (latest versions) and asking all packets
to
> >be enqueued to IMQ0 from both prerouting and postrouting (using different
> >iptables rules to mark different streams). When I do this I get the
kernel
> >saying:
> >
> >"Dead loop on netdevice imq0, fix it urgently!" and communications stop
> >intermittently. If I remove the jump from either preroute or postroute it
> >works fine but won't work together.
> >
> >Is this what is mean't to happen, because as far as I can see there is no
> >loop happening here?
> >
>
> You probably forward packets. The loop happening ist
> input-device -> prerouting -> imq (xmit_lock locked) -> reinject -> ...
> -> postrouting -> imq (LOCKED!!)
>
> To avoid this one has to drop xmit_lock in imq_xmit function before
> reinjecteing and grab it back afterwards.
> unfortunately this allows for endless recursion which is not possible in
> the kernel due to limited stack space.
> I've completed a version which should hopefully fix this as many people
> requested such a feature.
> I haven't released it yet because i have to do alot for my university
> atm and haven't got the time for testing
> although i promised the new version to some people for january ;(
> In about two weeks my semester-vacation start, i hope to release the new
> version very quickly afterwards.
>
> Thanks for your patience,
> Patrick
>
>

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