[Devel] Re: [PATCHSET] 2.6.20-rc4-mm1-lxc2

[Daniel Lezcano]

Cedric Le Goater wrote:
> All,
> 
> We've been gathering and porting patches related to namespaces in
> a lxc patchset for a while now. Mostly working on the network
> namespace which will require some extra work to be usable. 
> 
>  * It's available here :
> 
> 	http://www.sr71.net/patches/2.6.20/2.6.20-rc4-mm1-lxc2/
> 
> * Caveats :
> 
>   namespace syscalls are still under construction.
> 
>   network namespace is broken : 
> 
>   . the nsproxy backpointer in net_ns is flaky. 
>   . the push_net_ns() and pop_net_ns() can be called under 
>     irq and are using current. this seems inappropriate.
>   . there is a race on ->nsproxy between push_net_ns() and 
>     exit_task_namespaces()

Hi Dmitry,

we are experiencing NULL address access when using the nsproxy in 
push_net_ns function without any unshare.

It appears the exit_task_namespace function sets current->nsproxy to 
NULL and we are interrupted by an incoming packet. The netif_receive_skb 
does push_net_ns(dev->net_ns). The push_net_ns function retrieves the 
current->nsproxy to use it. But it was previously set to NULL by the 
exit_task_namespace function.

The bug can be reproduced with the following command launched from 
another host.

while $(true); do ssh myaddress ls > /dev/null && echo -n .; done

After a time (between 1 second - 3 minutes), the kernel panics.

I think this will be very hard to fix and perhaps we should redesign 
some part. Instead of using nsproxy swapping, perhaps we should pass 
net_ns as parameter to functions, but that will breaks a lot of API.

What is your feeling on that ?

Regards.

   -- Daniel.
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