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

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Date:	Fri, 12 Jun 2015 16:55:55 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	Andy Lutomirski <luto@...capital.net>
CC:	"David S. Miller" <davem@...emloft.net>,
	Ingo Molnar <mingo@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Wang Nan <wangnan0@...wei.com>, Li Zefan <lizefan@...wei.com>,
	Daniel Wagner <daniel.wagner@...-carit.de>,
	Daniel Borkmann <daniel@...earbox.net>,
	Linux API <linux-api@...r.kernel.org>,
	Network Development <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next 1/3] bpf: introduce current->pid, tgid, uid,
 gid, comm accessors

On 6/12/15 4:47 PM, Andy Lutomirski wrote:
> On Fri, Jun 12, 2015 at 4:38 PM, Alexei Starovoitov <ast@...mgrid.com> 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.

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