Re: [RFC][PATCH] VFS: create /proc//mountinfo

Ram Pai
2008-01-21T21:55:16Z

On Mon, 2008-01-21 at 22:25 +0100, Miklos Szeredi wrote:
> > You have removed the code that checked if the peer or
> > master mount was in the same namespace before reporting their
> > corresponding mount-ids. One downside of that approach is the
> > user will see an mount_id in the output with no corresponding
> > line to explain the details of the mount_id.
>
> Before the change, the peer and master ID's were basically randomly
> chosen from the peers, which means, it wasn't possible to always
> determine, that two mounts were peers, or that they were slaves to the
> same peer group.
>
> After the change, this is possible, since the peer ID will be the same
> for all mounts which are peers. This means, that even though the peer
> ID might be in a different namespace, it is possible to determine all
> peers within the same namespace by comparing their peer ID's.

I agree with your reasoning on the random id; showing a single
id avoids clutter. But my point is, why not show a
id for the master or peer residing in the same namespace?
Showing a id with no corresponding entry for that id, can be
intriguing.

If no master-mount exists in the same namespace then print -1
meaning "masked".

there is always atleast one peer-mount in a given namespace; so no
issue there.

> >
> > And reporting the mount-id of a mount is some other namespace
> > could subtly mean information-leak?
>
> I don't think the mount ID itself can be sensitive, it really doesn't
> contain any information, other than being an identifier.
>
> > One other comment I had received offline from Steve French was
> > that the patch did not consider the following case:
> >
> > "Have you thought about whether this could handle the case in which cifs mounts with
> > a relative path e.g. currently
> > mount -t cifs //server/share /mnt
> >
> > can not be distinguished from
> > mount -t cifs //server/share/subdirectory /mnt
> >
> > when you run the mount command (ie the cifs "prefixpath" in this case
> > "/subdirectory" is not displayed)"
>
> Why cifs not displaying '//server/share/subdirectory' as the source of
> the mount?

dont know. not tried it myself.

RP
>
> Miklos