Re: [PATCH net-next 1/3] bpf: introduce current->pid, tgid, uid, gid, comm accessors

[Alexei Starovoitov]

On 6/12/15 5:03 PM, Andy Lutomirski wrote:
> On Fri, Jun 12, 2015 at 4:55 PM, Alexei Starovoitov <ast@xxxxxxxxxxxx> wrote:
> > On 6/12/15 4:47 PM, Andy Lutomirski wrote:
> > > On Fri, Jun 12, 2015 at 4:38 PM, Alexei Starovoitov <ast@xxxxxxxxxxxx>
> > > wrote:
> > > > On 6/12/15 4:25 PM, Andy Lutomirski wrote:
> > > > > It's a dangerous tool.  Also, shouldn't the returned uid match the
> > > > > namespace of the task that installed the probe, not the task that's
> > > > > being probed?
> > > >
> > > >
> > > >
> > > > so leaking info to unprivileged apps is the concern?
> > > > The whole thing is for root only as you know.
> > > > The non-root is still far away. Today root needs to see the whole
> > > > kernel. That was the goal from the beginning.
> > >
> > > This is more of a correctness issue than a security issue.  ISTM using
> > > current_user_ns() in a kprobe is asking for trouble.  It certainly
> > > allows any unprivilege user to show any uid it wants to the probe,
> > > which is probably not what the installer of the probe expects.
> >
> >
> > probe doesn't expect anything. it doesn't make any decisions.
> > bpf is read only. it's _visibility_ into the kernel.
> > It's not used for security.
> > When we start connecting eBPF to seccomp I would agree that uid
> > handling needs to be done carefully, but we're not there yet.
> > I don't want to kill _visibility_ because in some distant future
> > bpf becomes a decision making tool in security area and
> > get_current_uid() will return numbers that shouldn't be blindly
> > used to reject/accept a user requesting something. That's far away.
>
> All that is true, but the code that *installed* the bpf probe might
> get might confused when it logs that uid 0 did such-and-such when
> really some unprivileged userns root did it.

so what specifically you proposing?
Use from_kuid(&init_user_ns,...) instead?

> Also, as you start calling more and more non-trivial functions from
> bpf, you might need to start preventing bpf probe installations in
> those functions.

yes. may be. I don't want to blacklist stuff yet, unless it
causes crashes. Recursive check is already there. Probably
something else will be needed.

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