Re: [RCF] [PATCH] unprivileged mount/umount
From: Ram (linuxram_at_us.ibm.com)
Date: 05/13/05
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To: Miklos Szeredi <miklos@szeredi.hu> Date: Fri, 13 May 2005 01:59:40 -0700
On Fri, 2005-05-13 at 00:25, Ram wrote:
> 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 :)
attached a patch that can fix the problem, if everybody agrees that its
a problem.
> RP
>
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