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=-2.2 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 37F54C33CB3 for ; Tue, 28 Jan 2020 19:42:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 02389206A2 for ; Tue, 28 Jan 2020 19:42:36 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=kernel-dk.20150623.gappssmtp.com header.i=@kernel-dk.20150623.gappssmtp.com header.b="NCpei043" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726143AbgA1Tmf (ORCPT ); Tue, 28 Jan 2020 14:42:35 -0500 Received: from mail-io1-f65.google.com ([209.85.166.65]:40430 "EHLO mail-io1-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726066AbgA1Tmf (ORCPT ); Tue, 28 Jan 2020 14:42:35 -0500 Received: by mail-io1-f65.google.com with SMTP id x1so15771639iop.7 for ; Tue, 28 Jan 2020 11:42:34 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel-dk.20150623.gappssmtp.com; s=20150623; h=subject:from:to:cc:references:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=cficbeQi0omLSQ5aB+E1peoKmYMRi/UKI45hekpbJJE=; b=NCpei043MopK1q15HT40ka5PtNTznQmAUxAClRwpXixcrYrcUUijAM7bGWtOAhlH28 ClYuoC4n9GmQD72DWBwxJrlUsCZ6n8SCeqo4M5s2hKP2/+NS7n4rCHexhLgV/po1LZP1 I5LDZ+N7todVlDRG4WKR6FcG83CF3mH95mWsnpHW3y8Viq3JVtb3s0/0HcgnpLjmuIZO /Xjkd3O/H02Y3Eiq9e06VEbUrtdumhKZcNgG3reat1C8mmJ2RWVo1V/B1kT7515L3pmF xypXfVi0os2zhAhgOgA/bMGeEhvjG9mVmrSz0mUuxP3gXQYT2NG2Ja66lcaTTCFgLQEP 4WEw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:from:to:cc:references:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=cficbeQi0omLSQ5aB+E1peoKmYMRi/UKI45hekpbJJE=; b=dgTV66c6zCEOZh509AFRXEj3KqbnixAoqVJ2VcHleRYT42JZ4lcMD1tF3xQRU9J9KO du3ILpk07Uk+YwqgxQOIVzzQP/u3GWXOB+wfyXL+HLcgO6LTiPOb3Bet3jZht5UefrOv BkVSTnpxseQENgEtGfG//4ukuk54zQul8UTWglWNyxDdac2mNsp9B4LfE/SHEjED2Hyo EynSN0enS/2VMoan0/1StW3X+IiB7vrjEnTGKNaV3xyxaYFwVmle+dMZBjQgh1zNvH2J aIdyXl+ZB6nf00S9/VHdSBJ25MTIIJgNRoxgpIJAcycd3a+VBR2FQUOY85V3LMXBo2tB 5Nqw== X-Gm-Message-State: APjAAAUh8rGmvRxB39gYgkeSzYcMd1iHMN9nexFBTgGFh/iC/5Dfp6+5 uwpnNObbtesU0MmJjBzUjwUSsw== X-Google-Smtp-Source: APXvYqyc/0Yu8YMWgviWXHCV41mMmiqboCZnKL3O8Rh79koUfRqQ0ej82STukfEZv34HyNLgRrKiIQ== X-Received: by 2002:a02:51c3:: with SMTP id s186mr9929271jaa.127.1580240554275; Tue, 28 Jan 2020 11:42:34 -0800 (PST) Received: from [192.168.1.159] ([65.144.74.34]) by smtp.gmail.com with ESMTPSA id w5sm4662481iob.26.2020.01.28.11.42.33 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 28 Jan 2020 11:42:33 -0800 (PST) Subject: Re: IORING_REGISTER_CREDS[_UPDATE]() and credfd_create()? From: Jens Axboe To: Stefan Metzmacher Cc: io-uring , Linux API Mailing List , Pavel Begunkov References: <688e187a-75dd-89d9-921c-67de228605ce@samba.org> <1ac31828-e915-6180-cdb4-36685442ea75@kernel.dk> <0d4f43d8-a0c4-920b-5b8f-127c1c5a3fad@kernel.dk> Message-ID: Date: Tue, 28 Jan 2020 12:42:32 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: <0d4f43d8-a0c4-920b-5b8f-127c1c5a3fad@kernel.dk> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: io-uring-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 1/28/20 11:04 AM, Jens Axboe wrote: > On 1/28/20 10:19 AM, Jens Axboe wrote: >> On 1/28/20 9:19 AM, Jens Axboe wrote: >>> On 1/28/20 9:17 AM, Stefan Metzmacher wrote: >>>> Am 28.01.20 um 17:10 schrieb Jens Axboe: >>>>> On 1/28/20 3:18 AM, Stefan Metzmacher wrote: >>>>>> Hi Jens, >>>>>> >>>>>> now that we have IORING_FEAT_CUR_PERSONALITY... >>>>>> >>>>>> How can we optimize the fileserver case now, in order to avoid the >>>>>> overhead of always calling 5 syscalls before io_uring_enter()?: >>>>>> >>>>>> /* gain root again */ >>>>>> setresuid(-1,0,-1); setresgid(-1,0,-1) >>>>>> /* impersonate the user with groups */ >>>>>> setgroups(num, grps); setresgid(-1,gid,-1); setresuid(-1,uid,-1); >>>>>> /* trigger the operation */ >>>>>> io_uring_enter(); >>>>>> >>>>>> I guess some kind of IORING_REGISTER_CREDS[_UPDATE] would be >>>>>> good, together with a IOSQE_FIXED_CREDS in order to specify >>>>>> credentials per operation. >>>>>> >>>>>> Or we make it much more generic and introduce a credsfd_create() >>>>>> syscall in order to get an fd for a credential handle, maybe >>>>>> together with another syscall to activate the credentials of >>>>>> the current thread (or let a write to the fd trigger the activation >>>>>> in order to avoid an additional syscall number). >>>>>> >>>>>> Having just an fd would allow IORING_REGISTER_CREDS[_UPDATE] >>>>>> to be just an array of int values instead of a more complex >>>>>> structure to define the credentials. >>>>> >>>>> I'd rather avoid having to add more infrastructure for this, even if >>>>> credsfd_create() would be nifty. >>>>> >>>>> With that in mind, something like: >>>>> >>>>> - Application does IORING_REGISTER_CREDS, which returns some index >>>>> >>>>> - Add a IORING_OP_USE_CREDS opcode, which sets the creds associated >>>>> with dependent commands >>>>> - Actual request is linked to the IORING_OP_USE_CREDS command, any >>>>> link off IORING_OP_USE_CREDS will use those credentials >>>> >>>> Using links for this sounds ok. >>> >>> Great! I'll try and hack this up and see how it turns out. >>> >>>>> - IORING_UNREGISTER_CREDS removes the registered creds >>>>> >>>>> Just throwing that out there, definitely willing to entertain other >>>>> methods that make sense for this. Trying to avoid needing to put this >>>>> information in the SQE itself, hence the idea to use a chain of links >>>>> for it. >>>>> >>>>> The downside is that we'll need to maintain an array of key -> creds, >>>>> but that's probably not a big deal. >>>>> >>>>> What do you think? >>>> >>>> So IORING_REGISTER_CREDS would be a simple operation that just takes a >>>> snapshot of the current_cred() and returns an id that can be passed to >>>> IORING_OP_USE_CREDS or IORING_UNREGISTER_CREDS? >>> >>> Right, you would not pass in any arguments, it'd have to be run from the >>> personality you wish to register. It simply returns an integer, which is >>> a key to use for IORING_OP_USE_CREDS, or at the end for >>> IORING_UNREGISTER_CREDS when you no longer wish to use this personality. >>> >>>>> Ideally I'd like to get this done for 5.6 even if we >>>>> are a bit late, so you'll have everything you need with that release. >>>> >>>> That would be great! >>> >>> Crossing fingers... >> >> OK, so here are two patches for testing: >> >> https://git.kernel.dk/cgit/linux-block/log/?h=for-5.6/io_uring-vfs-creds >> >> #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'll try and write a test case for this just to see if it actually works, >> so far it's totally untested. >> >> Adding Pavel to the CC. > > Minor tweak to ensuring we do the right thing for async offload as well, > and it tests fine for me. Test case is: > > - Run as root > - Register personality for root > - create root only file > - check we can IORING_OP_OPENAT the file > - switch to user id test > - check we cannot IORING_OP_OPENAT the file > - check that we can open the file with IORING_OP_USE_CREDS linked 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. -- Jens Axboe