Messages in this thread | | | Date | Tue, 8 Oct 2013 12:42:02 +0200 | From | Matthias Schniedermeyer <> | Subject | Re: [RFC][PATCH 4/3] vfs: Allow rmdir to remove mounts in all but the current mount namespace |
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On 06.10.2013 23:55, Eric W. Biederman wrote: > "Serge E. Hallyn" <serge@hallyn.com> writes: > > So if we can feel safe just depending on the parent directory > permissions (which are not hidden by a mount) protecting our mount > points, I feel much better about this patchset.
As far as i can tell, the permissions of the host-directory of a mount-point are hidden, at least for user-space. (Ignoring (bind-)mounting the parent-mount somewhere else)
As root: $ mkdir /tmp/test $ ls -ld /tmp/test drwxr-xr-x 2 root root 40 Oct 8 12:33 /tmp/test
$ mount tmpfs -t tmpfs /tmp/test $ ls -ld /tmp/test drwxrwxrwt 2 root root 40 Oct 8 12:33 /tmp/test
$ chown nobody.users /tmp/test $ ls -ld /tmp/test drwxrwxrwt 2 nobody users 40 Oct 8 12:33 /tmp/test
$ umount /tmp/test $ ls -ld /tmp/test drwxr-xr-x 2 root root 40 Oct 8 12:33 /tmp/test
So if the kernel would check the host-directory-permissions for allowing umounting by rmdir it follows that a "plain user" doesn't have any possibility to know beforehand if rmdir/umount would be possible.
--
Matthias
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