Re: [RFC][PATCH] ns: Syscalls for better namespace sharing control.

[Daniel Lezcano <daniel.lezcano-GANU6spQydw@public.gmane.org>]

Eric W. Biederman wrote:
> Daniel Lezcano <daniel.lezcano-GANU6spQydw@public.gmane.org> writes:
>
>   
>> Eric W. Biederman wrote:
>>     
>
>   
>> If the normal rules of parentage apply, that means pid 0 has to wait it's child.
>> If we are in the scenario of pid 0, it's child pid 1234 and we kill the pid 1 of
>> the pid namespace, I suppose pid 1234 will be killed too.
>> The pid 0 will stay in the pid namespace and will able to fork again a new pid
>> 1.
>>
>> I think Serge already reported that...
>>
>> That sounds good :)
>>     
>
> I expect zap_pid_ns_processes should also arrange so we cannot allocate any
> more processes.  We certainly need to do something explicit or pid 1 won't
> be allocated.  It might make sense to resurrect a pid namespace after it's
> death but it is definitely weird.
>   
Mmh, yes. But that was just an idea, maybe a bit out of the scope you 
are aiming.

>>> In a lot of ways I like this idea of sys_hijack/sys_cloneat, and I
>>> don't think anything I am doing fundamentally undermines it.  The use
>>> case of doing things in fork is that there is automatic inheritance of
>>> everything.  All of the namespaces and all of the control groups, and
>>> possibly also the parent process.  
>>>       
>> And also the rootfs for executing the command inside the container
>> (eg. shutdown), the uid/gid (if there is a user namespace), the mount points,
>> ...
>> But I suppose we can do the same with setns for all the namespaces and chrooting
>> within the container rootfs.
>>
>> What I see is a problem with the tty. For example, we cloneat the init process
>> of the container which is usually /sbin/init but this one has its tty mapped to
>> /dev/console, so the output of the exec'ed command will go to the console.
>>     
>
> My original thinking was that the fd's would come from the caller of sys_cloneat....
Oh, ok :s

>>> Overall it sounds like the semantics I have proposed with
>>> unshare(CLONE_NEWPID) are workable, and simple to implement.  The
>>> extra fork is a bit surprising but it certainly does not
>>> look like a show stopper for implementing a pid namespace join.
>>>   
>>>       
>> I agree, it's some kind of "ghost" process.
>> IMO, with a bit of userspace code it would be possible to enter or exec a
>> command inside a container with nsfd, setns.
>>
>> +1 to test your patchset Eric :)
>>     
>
> I will see about reposting sometime soon.
>   
Great ! thanks.

>> Just a mindless suggestion, the "nsopen" / "nsattach" syscall names should be
>> more clear no ?
>>     
>
> Not bad suggestions.
>
> I am going to explore a bit more.  Given that nsfd is using the same
> permission checks as a proc file, I think I can just make it a proc
> file.  Something like "/proc/<pid>/ns/net".  With a little luck that
> won't suck too badly.
>   
Ah ! yes. Good idea.