From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755284AbbFMAQF (ORCPT ); Fri, 12 Jun 2015 20:16:05 -0400 Received: from mail-pd0-f175.google.com ([209.85.192.175]:36479 "EHLO mail-pd0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753310AbbFMAQB (ORCPT ); Fri, 12 Jun 2015 20:16:01 -0400 Message-ID: <557B763F.7000003@plumgrid.com> Date: Fri, 12 Jun 2015 17:15:59 -0700 From: Alexei Starovoitov User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: Andy Lutomirski CC: "David S. Miller" , Ingo Molnar , Steven Rostedt , Wang Nan , Li Zefan , Daniel Wagner , Daniel Borkmann , Linux API , Network Development , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH net-next 1/3] bpf: introduce current->pid, tgid, uid, gid, comm accessors References: <1434145226-17892-1-git-send-email-ast@plumgrid.com> <1434145226-17892-2-git-send-email-ast@plumgrid.com> <557B60DB.5030200@plumgrid.com> <557B6A00.7000600@plumgrid.com> <557B6D74.2070305@plumgrid.com> <557B718B.80604@plumgrid.com> In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 6/12/15 5:03 PM, Andy Lutomirski wrote: > On Fri, Jun 12, 2015 at 4:55 PM, Alexei Starovoitov wrote: >> On 6/12/15 4:47 PM, Andy Lutomirski wrote: >>> >>> On Fri, Jun 12, 2015 at 4:38 PM, Alexei Starovoitov >>> 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.