linux-kernel - Re: [PATCH 2/2] KEYS: Add per-user_namespace registers for persistent per-UID kerberos caches

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Message-ID: <51FAAF3D.3010806@fifthhorseman.net>
Date:	Thu, 01 Aug 2013 14:55:57 -0400
From:	Daniel Kahn Gillmor <dkg@...thhorseman.net>
To:	Simo Sorce <simo@...hat.com>
CC:	David Howells <dhowells@...hat.com>, keyrings@...ux-nfs.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Serge E. Hallyn" <serge.hallyn@...ntu.com>,
	linux-nfs@...r.kernel.org, krbdev@....edu,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] KEYS: Add per-user_namespace registers for persistent
 per-UID kerberos caches

On 08/01/2013 02:29 PM, Simo Sorce wrote:

> It's called 'abstraction' :-)

Good, I like abstraction :)

>> It seems like a non-privileged user could use this to store arbitrary
>> data in this keyring as a way of hiding what would otherwise be
>> filesystem activity or using it for some sort of odd/sneaky IPC
>> mechanism.  Is this an intentional side effect?
> 
> Just as a user can add data into a shm segment ?
> Is there any difference ?

I guess this raises the question from a different perspective: if the
kernel already supports arbitrary shm segments, filesystem locations,
etc, which can be used for storing/passing opaque bytestrings between
different parts of userspace, what advantages do we gain from having
this new specific mechanism in the kernel?  Why couldn't those parts of
userspace just rely on already-existing mechanisms instead of
introducing this new interface?

Again, i'm not trying to say it's a bad idea; there's probably a
big-picture piece of the puzzle that i don't see that makes this all
obvious.  i just want to understand what it is.  Thanks for your
explanations!

Regards,

	--dkg

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