Re: [patch] PID namespace design bug, workaround

[david@lang.hm]

On Sat, 3 Nov 2007, Arjan van de Ven wrote:

> On Sat, 3 Nov 2007 15:40:48 -0700 (PDT)
> Linus Torvalds <torvalds@linux-foundation.org> wrote:
>
> > I don't understand how you can call this a "PID namespace design
> > bug", when it clearly has nothing what-so-ever to do with pid
> > namespaces, and everything to do with the *futexes* that blithely
> > assume that pid's are unique and that made it part of the
> > user-visible interface.
> >
> > OF COURSE any pid namespace design will always break such
> > assumptions, but that's not because of any PID namespace bugs. It's
> > what the whole *point* of PID namespaces are. If you use pid's
> > (instead of some opaque cookies), you will not be able to use such
> > things across pid-separation.
>
> well... kind of.
> THere are 2 things around pid namespaces: which pids you can see/touch
> (in proc or signals or otherwise), and the non-uniqueness.
>
> For containers you clearly want the first part... but... is there a
> strong reason to not just *not* create duplicate pids even across
> namespaces? there's no rule in posix or anything similar to fd's afaik
> concerning which pids we can hand out... so we could just make then
> unique globally but just with limited visibility....

two problems that I can think of

1. the container people would like to eventually have the ability to 
migrate containers from one system to another (or to suspend a container) 
in this sort of case trying to fit the allocated PIDs from the container 
into a running system is a problem if PIDs are not allowed to overlap.

2. it seems to me that there is porobably a latent security issue in 
having a global PID namespace with just limited visability. the types of 
bugs that may let you affect a process seem easier to make if the only 
protection is visability rather then complete seperation.

David Lang
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