Subject: Re: [RCF] [PATCH] unprivileged mount/umount
From: Ram <linuxram@us.ibm.com>
To: Miklos Szeredi <miklos@szeredi.hu>
Cc: jamie@shareable.org, ericvh@gmail.com, 7eggert@gmx.de,
       linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
       smfrench@austin.rr.com, hch@infradead.org
In-Reply-To: <1115946620.6248.299.camel@localhost>
References: <20050511170700.GC2141@mail.shareable.org>
	 <E1DVwGn-0002BB-00@dorka.pomaz.szeredi.hu>
	 <1115840139.6248.181.camel@localhost>
	 <20050511212810.GD5093@mail.shareable.org>
	 <1115851333.6248.225.camel@localhost>
	 <a4e6962a0505111558337dd903@mail.gmail.com>
	 <20050512010215.GB8457@mail.shareable.org>
	 <a4e6962a05051119181e53634e@mail.gmail.com>
	 <20050512064514.GA12315@mail.shareable.org>
	 <a4e6962a0505120623645c0947@mail.gmail.com>
	 <20050512151631.GA16310@mail.shareable.org>
	 <E1DWIms-0005nC-00@dorka.pomaz.szeredi.hu>
	 <1115946620.6248.299.camel@localhost>
Content-Type: text/plain
Organization: IBM 
Message-Id: <1115969123.6248.336.camel@localhost>
Mime-Version: 1.0
Date: Fri, 13 May 2005 00:25:24 -0700
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 2003
Lines: 50

On Thu, 2005-05-12 at 18:10, Ram wrote:
> On Thu, 2005-05-12 at 11:51, Miklos Szeredi wrote:
> > > > I'm not sure passing directory file descriptors is the right semantic
> > > > we want - but at least it provides a point of explicit control (in
> > > > much the same way as a bind).  Are you sure the clone + open("/") +
> > > > pass-to-parent scenario you allows the parent to traverse the child's
> > > > private name space through that fd?
> > > 
> > > Pretty sure.
> > 
> > Yup.  Attached a little program that can be used to try this out.  It
> > creates a new namespace in the child, does a bind mount (so the
> > namespaces can be differentiated), then sends the file descriptor of
> > "/" to the parent.  The parent does fchdir(fd), then starts a shell.
> 
> 
> > So the result is that CWD is under the child namespace, while root is
> > under the initial namespace.
> > 
> 
> r u sure, this program works? Sorry if I am saying something dumb here.
> Correct me.  When a file descriptor is sent from one process to other,
> arn't they referring to different files in each of the processes.
> fd=5 may be pointing to file 'xyz' in parent process, 
> where as fd=5 will be pointing to 'abc' in the child process.  
> 
> This program did not work for me, and I was wondering if adding
> CLONE_FILES in clone() would help. Because that would make sure
>  that both
> the processes share the same file descriptor. It did not work too.
> 
> What am I understanding wrong?

Sorry it works. I was misinterpreting the results. 

> 
> In any case my opinion is if this program works than the hole should
> be closed instead of exploting it to access different namespace. I 
> know Jamie is going to pounce at me. ;)

a patch is due to fix the problem :)

RP


-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/