Re: [PATCH -mm 5/7] add user namespace

[Cedric Le Goater <clg@fr.ibm.com>]

Eric W. Biederman wrote:

>> I think user namespace should be unshared with filesystem. if not, the
>> user/admin should know what is doing.
> 
> No.  The uids in a filesystem are interpreted in some user namespace
> context.  We can discover that context at the first mount of the
> filesystem. 

ok. so once you're in such a user namespace, you can't unshare from it
without loosing access to all your files ?

> Assuming the uids on a filesystem are the same set of uids your process
> is using is just wrong.

well, this is what is currently done without user namespaces.

>>> I believe some of the key infrastructure which is roughly kerberos
>>> authentication tokens could be used for this purpose.
>> please elaborate ? i'm not sure to understand why you want to use the keys
>> to map users.
> 
> keys are essentially security credentials for something besides the
> local kernel.  Think kerberos tickets.  That makes the keys the
> obvious place to say what uid you are in a different user namespace
> and similar things.

what about performance ? wouldn't that slow the checking ?

thanks,

C.