linux-kernel - Re: [PATCH 0/2] Fix /proc/net in presence of net namespaces

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Message-ID: <47C7BF4D.6020202@openvz.org>
Date:	Fri, 29 Feb 2008 11:16:13 +0300
From:	Pavel Emelyanov <xemul@...nvz.org>
To:	serge@...lyn.com
CC:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Miller <davem@...emloft.net>,
	Alexey Dobriyan <adobriyan@...nvz.org>,
	Linux Netdev List <netdev@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/2] Fix /proc/net in presence of net namespaces

[snip]

>> However at least for visibility and inspection we want that.
>> We want to inspect what is happening to other processes.  If we didn't
>> care then all of the pid namespaces could just be disjoint.
> 
> But the way Pavel has it coded, only tasks in the init namespace can
> view /proc/.net/* for any other net namespaces.

This is not essential part of the patch :) I did so to make my
life in init namespace easier. This part can be dropped.

[snip]

>> Think of user space processes inspecting /proc etc.
> 
> Well a task in one pid namespace cannot view the /proc for another pid
> namespace, right?

No. Pid namespace provides another pid-to-task map, but have noting
to do with VFS visibility.

>> Having directory
>> names change out form under you for no apparent reason is pretty nasty.
> 
> Yes, but they won't just 'change out' from under you, you ask for it...
> But here like I said I do prefer an approach where /proc/net is bind
> mounted by the user.  But I have no good reason to back it up...

If you make /proc/net be a bund mount then you have to force all of
the users to update their init scripts. I tried to make so with sysctl 
filesystem, but this thread was not very popular :)

Another way to do so - is to mount this one from inside the kernel, 
but are you ready to fight with Al Viro for this? :)

[snip]

>> So I think /proc/.netns/ or simply /proc/netns/ is a good choice. We
>> just need a non-global id for our directory entries so we don't paint
>> ourselves into a corner.
> 
> But I don't see how this is going to work.  If you're using a pid_nr
> inside a pid namespace, then you're not guaranteeing that the pid_nr
> will be unique, so you may not be able to create th e/proc/.netns/X
> directory.  If you're using the global pid, then you're not guaranteeing
> that it will be available upon a container restart.

Right - this is the same as using other ids, which I propose.

>> And honestly pid visibility is a very natural choice for which network
>> namespaces you can see.  You can see the namespace of any process you
>> can see.  Which especially means your children.  It is an arbitrary
>> rule, it is a simple rule to explain, and it works recursively unlike
> 
> But apparently not simple enough for a simpleton like me to understand,
> sorry :(
> 
>> any init_net is special rule.
>>
>> Eric
> 

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