linux-kernel - Re: [PATCH 3/4] autofs4 - track uid and gid of last mount requestor

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Message-ID: <20080228195118.GA16634@sergelap.austin.ibm.com>
Date:	Thu, 28 Feb 2008 13:51:18 -0600
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	Jeff Moyer <jmoyer@...hat.com>
Cc:	Ian Kent <raven@...maw.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kernel Mailing List <linux-kernel@...r.kernel.org>,
	autofs mailing list <autofs@...ux.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Pavel Emelyanov <xemul@...nvz.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH 3/4] autofs4 - track uid and gid of last mount requestor

Quoting Jeff Moyer (jmoyer@...hat.com):
> Ian Kent <raven@...maw.net> writes:
> 
> > On Wed, 2008-02-27 at 23:23 -0800, Andrew Morton wrote:
> >> On Thu, 28 Feb 2008 16:08:20 +0900 Ian Kent <raven@...maw.net> wrote:
> >> > which includes the process uid and gid, and as part of
> >> > the lookup we set macros for several mount map substitution variables,
> >> > derived from the uid and gid of the process requesting the mount and
> >> > they can be used within autofs maps.
> >> 
> >> yeah, could be a problem.  Hopefully the namespace people can advise. 
> >> Perhaps we need a concept of an exportable-to-userspace namespace-id+uid,
> >> namespace-id+gid, namespace-id+pid, etc for this sort of thing.  It has
> >> come up before.  Recently, but I forget what the context was.
> >
> > I'm all ears to any feedback from others on this, please.
> 
> I think there is some confusion surrounding what the UID and GID are
> used for in this context.  I'll try to explain it as best I can.
> 
> When the automount daemon parses a map entry, it will do some amount of
> variable substitution.  So, let's say you're running on an i386 box, and
> you want to mount a library directory from a server.  You might have a
> map entry that looks like this:
> 
> lib	server:/export/$ARCH/lib
> 
> In this case, the automount daemon will replace $ARCH with i386, and
> will try the following mount command:
> 
> mount -t nfs server:/export/i386/lib /automountdir/lib
> 
> There are cases where it would be helpful to use the requesting
> process's UID in such a variable substitution.  Consider the case of a
> CIFS share, where the automount daemon runs as user root, but we want to
> mount the share using the credentials of the requesting user.  In this
> case, the UID and GID can be helpful in formatting the mount options for
> mounting the share.
> 
> So, the UID and GID are used only for map substitutions.  Now, having
> said all of that, I'll have to look more closely at why we even need to
> keep track of it, given that it only needs to be used when performing
> the lookup, and at that time we have information on the requesting UID
> and GID.

Thanks Jeff.  If that's the case then user namespaces don't affect this
at all.

(Still trying to follow the rest of the thread bc i definately feel like
I'm missing something.  I swear I understood autofs 10+ years ago :)

thanks,
-serge
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