Messages in this thread | | | From | (Eric W. Biederman) | Date | Tue, 07 Oct 2014 13:52:35 -0700 | Subject | Re: [PATCH] [RFC] mnt: add ability to clone mntns starting with the current root |
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Serge Hallyn <serge.hallyn@ubuntu.com> writes:
> Quoting Eric W. Biederman (ebiederm@xmission.com): >> Al Viro <viro@ZenIV.linux.org.uk> writes: >> >> 2> On Tue, Oct 07, 2014 at 02:30:40PM +0100, Al Viro wrote: >> >> On Tue, Oct 07, 2014 at 04:12:57PM +0400, Andrey Vagin wrote: >> >> > Another problem is that rootfs can't be hidden from a container, because >> >> > rootfs can't be moved or umounted. >> >> >> >> ... which is a bug in mntns_install(), AFAICS. >> > >> > Ability to get to exposed rootfs, that is. >> >> The container side of this argument is pretty bogus. It only applies >> if user namespaces are not used for the container. > > User namespaces are still far too restricted for many container use > cases. We can't say "we have user namespaces so now privileged > containers can be ignored". Yes you never should have handed the > keys to a privileged container to an untrusted person, but we do > still try to protect the host from accidental damage due to a > privileged container.
What I meant is that it isn't about containers. It is about something root can do. So this is not a "container" problem.
>> So it is only root (and not root in a container) who can get to the >> exposed rootfs. >> >> I have a vague memory someone actually had a real use in miminal systems >> for being able to get back to the rootfs and being able to use rootfs as >> the rootfs. There was even a patch at that time that Andrew Morton was >> carrying for a time to allow unmounting root and get at rootfs, and to >> prevent the oops on rootfs unmount in some way. >> >> So not only do I not think it is a bug to get back too rootfs, I think >> it is a feature that some people have expressed at least half-way sane >> uses for. > > They can still do that if they want, using chroot :)
It would take fchdir or fchroot and a directory file descriptor open on rootfs. Frequently there is no appropriate directory file descriptor.
Eric
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