Hello Eric,
>>> Creating of a mount namespace in a user namespace automatically does
>>> 'mount("", "/", MS_SLAVE | MS_REC, NULL);' if the starting mount
>>> namespace was not created in that user namespace. AKA creating
>>> a mount namespace in a user namespace does the unshare for you.
>>
>> Oh -- I had forgotten that detail. But it is documented
>> (by you, I think) in mount_namespaces(7):
>>
>> * A mount namespace has an owner user namespace. A
>> mount namespace whose owner user namespace is differ‐
>> ent from the owner user namespace of its parent mount
>> namespace is considered a less privileged mount names‐
>> pace.
>>
>> * When creating a less privileged mount namespace,
>> shared mounts are reduced to slave mounts. (Shared
>> and slave mounts are discussed below.) This ensures
>> that mappings performed in less privileged mount
>> namespaces will not propagate to more privileged mount
>> namespaces.
>>
>> There's one point that description that troubles me. There is a
>> reference to "parent mount namespace", but as I understand things
>> there is no parental relationship among mount namespaces instances
>> (or am I wrong?). Should that wording not be rather something
>> like "the mount namespace of the process that created this mount
>> namespace"?
>
> How about "the mount namespace this mount namespace started as a copy of"
>
> You are absolutely correct there is no relationship between mount
> namespaces. There is just the propagation tree between mounts. (Which
> acts similarly to a parent/child relationship but is not at all the same
> thing).
Thanks. I made the text as follows:
* Each mount namespace has an owner user namespace. As noted
above, when a new mount namespace is created, it inherits a
copy of the mount points from the mount namespace of the
process that created the new mount namespace. If the two mount
namespaces are owned by different user namespaces, then the new
mount namespace is considered less privileged.
Cheers,
Michael
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
