Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759336AbbGHRkM (ORCPT ); Wed, 8 Jul 2015 13:40:12 -0400 Received: from mail-la0-f46.google.com ([209.85.215.46]:35206 "EHLO mail-la0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759318AbbGHRkH (ORCPT ); Wed, 8 Jul 2015 13:40:07 -0400 MIME-Version: 1.0 In-Reply-To: <20150708161022.GA1705@odin.com> References: <1436172445-6979-1-git-send-email-avagin@openvz.org> <20150707154345.GA1593@odin.com> <20150708161022.GA1705@odin.com> From: Andy Lutomirski Date: Wed, 8 Jul 2015 10:39:45 -0700 Message-ID: Subject: Re: [PATCH 0/24] kernel: add a netlink interface to get information about processes (v2) To: Andrew Vagin Cc: Andrey Vagin , "linux-kernel@vger.kernel.org" , Linux API , Oleg Nesterov , Andrew Morton , Cyrill Gorcunov , Pavel Emelyanov , Roger Luethi , Arnd Bergmann , Arnaldo Carvalho de Melo , David Ahern , Pavel Odintsov Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3354 Lines: 68 On Wed, Jul 8, 2015 at 9:10 AM, Andrew Vagin wrote: > On Tue, Jul 07, 2015 at 08:56:37AM -0700, Andy Lutomirski wrote: >> On Tue, Jul 7, 2015 at 8:43 AM, Andrew Vagin wrote: >> > On Mon, Jul 06, 2015 at 10:10:32AM -0700, Andy Lutomirski wrote: >> >> On Mon, Jul 6, 2015 at 1:47 AM, Andrey Vagin wrote: >> >> > Currently we use the proc file system, where all information are >> >> > presented in text files, what is convenient for humans. But if we need >> >> > to get information about processes from code (e.g. in C), the procfs >> >> > doesn't look so cool. >> >> > >> >> > From code we would prefer to get information in binary format and to be >> >> > able to specify which information and for which tasks are required. Here >> >> > is a new interface with all these features, which is called task_diag. >> >> > In addition it's much faster than procfs. >> >> > >> >> > task_diag is based on netlink sockets and looks like socket-diag, which >> >> > is used to get information about sockets. >> >> >> >> I think I like this in principle, but I have can see a few potential >> >> problems with using netlink for this: >> >> >> >> 1. Netlink very naturally handles net namespaces, but it doesn't >> >> naturally handle any other kind of namespace. In fact, the taskstats >> >> code that you're building on has highly broken user and pid namespace >> >> support. (Look for some obviously useless init_user_ns and >> >> init_pid_ns references. But that's only the obvious problem. That >> >> code calls current_user_ns() and task_active_pid_ns(current) from >> >> .doit, which is, in turn, called from sys_write, and looking at >> >> current's security state from sys_write is a big no-no.) >> >> >> >> You could partially fix it by looking at f_cred's namespaces, but that >> >> would be a change of what it means to create a netlink socket, and I'm >> >> not sure that's a good idea. >> > >> > If I don't miss something, all problems around pidns and userns are >> > related with multicast functionality. task_diag is using >> > request/response scheme and doesn't send multicast packets. >> >> It has nothing to do with multicast. task_diag needs to know what >> pidns and userns to use for a request, but netlink isn't set up to >> give you any reasonably way to do that. A netlink socket is >> fundamentally tied to a *net* ns (it's a socket, after all). But you >> can send it requests using write(2), and calling current_user_ns() >> from write(2) is bad. There's a long history of bugs and >> vulnerabilities related to thinking that current_cred() and similar >> are acceptable things to use in write(2) implementations. >> > > As far as I understand, socket_diag doesn't have this problem, becaus > each socket has a link on a namespace where it was created. > > What if we will pin the current pidns and credentials to a task_diag > socket in a moment when it's created. That's certainly doable. OTOH, if anything does: socket(AF_NETLINK, ...); unshare(CLONE_PID); fork(); then they now have a (minor) security problem. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/