[Devel] Re: [patch -mm 08/17] nsproxy: add hashtable

[Eric W. Biederman]

"Serge E. Hallyn" <serue at us.ibm.com> writes:

> Quoting Serge E. Hallyn (serue at us.ibm.com):
>> Quoting Eric W. Biederman (ebiederm at xmission.com):
>> > Herbert Poetzl <herbert at 13thfloor.at> writes:
>> > >> Beyond that yes it seems to make sense to let user space
>> > >> maintain any mapping of containers to ids.
>> > >
>> > > I agree with that, but we need something to move
>> > > around between the various spaces ...
>> >
>> > If you have CAP_SYS_PTRACE or you have a child process
>> > in a container you can create another with ptrace.
>> >
>> > Now I don't mind optimizing that case, with something like
>> > the proposed bind_ns syscall.  But we need to be darn certain
>> > why it is safe, and does not change the security model that
>> > we currently have.
>> 
>> Sigh, and that's going to have to be a discussion per namespace.
>
> Well, assuming that we're using pids as identifiers, that means
> we can only enter decendent namespaces, which means 'we' must
> have created them.  So anything we could do by entering the ns,
> we could have done by creating it as well, right?

It isn't strict descendents who we can see.  i.e.  init can create
the thing, and we could have just logged into the network but init
and us still share the same pid namespace.

But yes it would be we can only enter descendent namespaces, for
some definition of enter. 

There are two issues.
1) We may have a namespace we want to create and then remove the ability
   for the sysadmin to fiddle with, so it can play with encrypted data or
   something like that safely.  Not quite unix but it is certainly worth
   considering.

2) When we only partially enter a namespace it is very easy for additional
   properties to enter that namespace.  For example we enter the pid
   namespace and the mount namespace, but keep our current working directory
   in the previous namespace.  Then a process in the restricted namespace
   can get out by cd into /proc/<?>/cwd.

If someones permissions to various objects does not depend on the namespace
they are in quite possibly this is a non-issue.  If we actually depend on
the isolation to keep things secure enter is a setup for a first rate escape.

Eric
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