From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id ABEE0C2D0DB for ; Thu, 30 Jan 2020 15:14:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 87FFA20678 for ; Thu, 30 Jan 2020 15:14:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727239AbgA3POJ (ORCPT ); Thu, 30 Jan 2020 10:14:09 -0500 Received: from youngberry.canonical.com ([91.189.89.112]:33261 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727238AbgA3POJ (ORCPT ); Thu, 30 Jan 2020 10:14:09 -0500 Received: from [109.134.33.162] (helo=wittgenstein) by youngberry.canonical.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.86_2) (envelope-from ) id 1ixBW5-0004Q2-IO; Thu, 30 Jan 2020 15:14:03 +0000 Date: Thu, 30 Jan 2020 16:13:42 +0100 From: Christian Brauner To: Jens Axboe Cc: Jann Horn , Stefan Metzmacher , io-uring , Linux API Mailing List , Pavel Begunkov Subject: Re: IORING_REGISTER_CREDS[_UPDATE]() and credfd_create()? Message-ID: <20200130151342.u554shnaliau42jq@wittgenstein> References: <1ac31828-e915-6180-cdb4-36685442ea75@kernel.dk> <0d4f43d8-a0c4-920b-5b8f-127c1c5a3fad@kernel.dk> <4f833fc5-b4c0-c304-c3c2-f63c050b90a2@kernel.dk> <9ce2e571-ed84-211a-4e99-d830ecdaf0e2@kernel.dk> <20200130102635.ar2bohr7n4li2hyd@wittgenstein> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Sender: io-uring-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On Thu, Jan 30, 2020 at 07:11:08AM -0700, Jens Axboe wrote: > On 1/30/20 3:26 AM, Christian Brauner wrote: > > On Thu, Jan 30, 2020 at 11:11:58AM +0100, Jann Horn wrote: > >> On Thu, Jan 30, 2020 at 2:08 AM Jens Axboe wrote: > >>> On 1/29/20 10:34 AM, Jens Axboe wrote: > >>>> On 1/29/20 7:59 AM, Jann Horn wrote: > >>>>> On Tue, Jan 28, 2020 at 8:42 PM Jens Axboe wrote: > >>>>>> On 1/28/20 11:04 AM, Jens Axboe wrote: > >>>>>>> On 1/28/20 10:19 AM, Jens Axboe wrote: > >>>>> [...] > >>>>>>>> #1 adds support for registering the personality of the invoking task, > >>>>>>>> and #2 adds support for IORING_OP_USE_CREDS. Right now it's limited to > >>>>>>>> just having one link, it doesn't support a chain of them. > >>>>> [...] > >>>>>> I didn't like it becoming a bit too complicated, both in terms of > >>>>>> implementation and use. And the fact that we'd have to jump through > >>>>>> hoops to make this work for a full chain. > >>>>>> > >>>>>> So I punted and just added sqe->personality and IOSQE_PERSONALITY. > >>>>>> This makes it way easier to use. Same branch: > >>>>>> > >>>>>> https://git.kernel.dk/cgit/linux-block/log/?h=for-5.6/io_uring-vfs-creds > >>>>>> > >>>>>> I'd feel much better with this variant for 5.6. > >>>>> > >>>>> Some general feedback from an inspectability/debuggability perspective: > >>>>> > >>>>> At some point, it might be nice if you could add a .show_fdinfo > >>>>> handler to the io_uring_fops that makes it possible to get a rough > >>>>> overview over the state of the uring by reading /proc/$pid/fdinfo/$fd, > >>>>> just like e.g. eventfd (see eventfd_show_fdinfo()). It might be > >>>>> helpful for debugging to be able to see information about the fixed > >>>>> files and buffers that have been registered. Same for the > >>>>> personalities; that information might also be useful when someone is > >>>>> trying to figure out what privileges a running process actually has. > >>>> > >>>> Agree, that would be a very useful addition. I'll take a look at it. > >>> > >>> Jann, how much info are you looking for? Here's a rough start, just > >>> shows the number of registered files and buffers, and lists the > >>> personalities registered. We could also dump the buffer info for > >>> each of them, and ditto for the files. Not sure how much verbosity > >>> is acceptable in fdinfo? > >> > >> At the moment, I personally am just interested in this from the > >> perspective of being able to audit the state of personalities, to make > >> important information about the security state of processes visible. > >> > >> Good point about verbosity in fdinfo - I'm not sure about that myself either. Afaik, there's no rule here. I would expect that it shouldn't exceed 4096kb just because that is the limit that seems to be enforced for writes to proc files atm; other than that it should be the wild west. The fdinfo files are mostly interesting for anon_inode fds imho and the ones that come to mind right now simply don't have a lot of information to provide: eventfd timerfd seccomp_notify_fd Potentially, the mount fds from David could be extended in the future. (Side note: One thing that comes to mind is that we should probably enforce^Wdocument that all fdinfo files use CamelCase?) Christian