[Devel] Re: [PATCH 2/2] hijack: update task_alloc_security

[Serge E. Hallyn]

Quoting Crispin Cowan (crispin at crispincowan.com):
> Serge E. Hallyn wrote:
> > Quoting Crispin Cowan (crispin at crispincowan.com):
> >   
> >> I find that ptrace, specifically CAP_SYS_PTRACE, is overloaded. AppArmor
> >> is having problems because we have to choose between granting
> >> cap_sys_ptrace, or not allowing the process to read /proc/pid/self &
> >> such like. So there, the problem is that we have to grant too much power
> >> to a process to just let it read some /proc stuff about itself.
> >>
> >> Here the problem appears to be the other way. cap_sys_ptrace is powerful
> >> enough to mess with other user's processes on the system, but if ptrace
> >> gives you hijack, then that seems to give you the power to control
> >> processes in someone else's namespace.
> >>     
> > The user namespace patchset I'm working on right now to start having
> > signals respect user namespaces introduces CAP_NS_OVERRIDE.  Once that
> > is in, then hijack would require CAP_NS_OVERRIDE|CAP_SYS_PTRACE.
> >
> > Of course, since we're considering only allowing HIJACK_NS which is
> > only allowed into a different namespace, hijack would then always
> > require CAP_NS_OVERRIDE...
> >
> > Does that suffice?
> >   
> I think that CAP_NS_OVERRIDE|CAP_SYS_PTRACE is a problem because of the

Oops, yeah I meant &.

> | making ptrace more powerful than it is now. If you make it
> CAP_NS_OVERRIDE only, then the problem goes away.

I was seeing CAP_NS_OVERRIDE as more of a modifier to other
capabilities.  So (CAP_NS_OVERRIDE&CAP_KILL) means you can
signal processes in another namespace.
(CAP_NS_OVERRIDE&CAP_DAC_OVERRIDE) means you can override (currently
nonexistent) DAC file access checks in another user namespace.
(CAP_NS_OVERRIDE&CAP_MKNOD) means you can create devices which your
container isn't allowed to create.

Yup, this is all somewhat looking ahead...

-serge
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