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

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Message-ID: <51FAA0CC.7010106@fifthhorseman.net>
Date:	Thu, 01 Aug 2013 13:54:20 -0400
From:	Daniel Kahn Gillmor <dkg@...thhorseman.net>
To:	David Howells <dhowells@...hat.com>
CC:	keyrings@...ux-nfs.org, linux-nfs@...r.kernel.org, krbdev@....edu,
	"Serge E. Hallyn" <serge.hallyn@...ntu.com>,
	linux-kernel@...r.kernel.org, simo@...hat.com,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH 2/2] KEYS: Add per-user_namespace registers for persistent
 per-UID kerberos caches

On 08/01/2013 01:39 PM, David Howells wrote:
> The uid is -1 or the user's own UID for the user's own cache or the uid of some
> other user's cache (requires CAP_SETUID).  This permits rpc.gssd or whatever to
> mess with the cache.

Is the goal here eventually to be able to avoid the upcall to rpc.gssd
entirely?  It seems a little bit roundabout to have the kernel call up
into userspace for the credentials, only to talk to a process which then
calls back into the kernel for something that the kernel has already
well-defined internally.

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?

Sorry if these are obvious questions.  feel free to point me to
already-documented answers if they exist.

Thanks for all your work on this!

Regards,

	--dkg

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