linux-kernel - Re: [patch] unprivileged mounts update

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Date:	Thu, 26 Apr 2007 22:10:31 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	jengelh@...ux01.gwdg.de, akpm@...ux-foundation.org,
	serue@...ibm.com, viro@....linux.org.uk, linuxram@...ibm.com,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	containers@...ts.osdl.org, hpa@...or.com
Subject: Re: [patch] unprivileged mounts update

Miklos Szeredi <miklos@...redi.hu> writes:

>> On Apr 25 2007 11:21, Eric W. Biederman wrote:
>> >>
>> >> Why did we want to use fsuid, exactly?
>> >
>> >- Because ruid is completely the wrong thing we want mounts owned
>> >  by whomever's permissions we are using to perform the mount.
>> 
>> Think nfs. I access some nfs file as an unprivileged user. knfsd, by
>> nature, would run as euid=0, uid=0, but it needs fsuid=jengelh for
>> most permission logic to work as expected.
>
> I don't think knfsd will ever want to call mount(2).
>
> But yeah, I've been convinced, that using fsuid is the right thing to
> do.

Actually knfsd does call mount when it crosses a mount point on the nfs
server it generates an equivalent mount point in linux.  At least I think
that is the what it is doing.  It is very similar to our mount propagation
path.

However as a special case I don't think the permission checking is likely
to bite us there.  It is worth double checking once we have the other details
ironed out.

Eric
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