On 06.10.2013 23:55, Eric W. Biederman wrote: > "Serge E. Hallyn" <serge@xxxxxxxxxx> 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 -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
