Andy Lutomirski <[email protected]> writes:

> On Thu, Feb 19, 2015 at 8:38 AM, Alexander Larsson <[email protected]> wrote:
>> On Tue, 2015-02-17 at 13:23 -0800, Andy Lutomirski wrote:
>>
>>>  - setuid / privileged helper.  Why do you need a privileged helper?
>>> You should be able to do all of this using user namespaces.  The
>>> Sandstorm code linked above does exactly this.
>>
>> I tried this a bit, but i ran into two snags i don't understand.
>>
>> First of all, as uid/gid 1000 i can put "1000 1000 1"
>> in /proc/self/uid_map from the child. However, i cannot put "1000 1000
>> 1" into gid_map, as i get EPERM.
>> I don't understand this, is this not supposed to work?
>
> You need newer manpages :-/  Try the attached variant.

Yeah.  You need to disable setgroups for that to work.

>> Secondly, i'm failing to mount another instance of devpts. It fails with
>> EINVAL.
>
> Hmm.  Off the top of my head, there's no good reason that devpts with
> the newinstance option couldn't be allowed in a userns.  Eric, any
> thoughts here?  The patch would be straightforward.

Looking at the code you have to have uid 0 and gid 0 mapped and you have
to specify newinstance.  But devepts is mountable without being the
global root user.

The restriction of having uid 0 and gid 0 mapped is just that /dev/ptmx is
and has alwasy been owned by root and so mknod_ptmx just won't let you
create a device inode as with a uid or gid you can't map.

Eric
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