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=-2.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 77DD5C2D0DB for ; Wed, 29 Jan 2020 13:41:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 401AB2071E for ; Wed, 29 Jan 2020 13:41:29 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="ZzSj0KFU" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726186AbgA2Nl2 (ORCPT ); Wed, 29 Jan 2020 08:41:28 -0500 Received: from mail-lf1-f65.google.com ([209.85.167.65]:45367 "EHLO mail-lf1-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726178AbgA2Nl2 (ORCPT ); Wed, 29 Jan 2020 08:41:28 -0500 Received: by mail-lf1-f65.google.com with SMTP id 203so11875579lfa.12; Wed, 29 Jan 2020 05:41:26 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=l0u5WHmdUM6QOorSCuU0hXeCuOESdwfl8W0or7sC/p0=; b=ZzSj0KFUsblFkfZ8JM1YmuLQtJz39EMqJr/AwhnmBpeJVwCKJLWeA2KL8figj6KLM4 5pl+cxLNpIjKM5fuTNsvcv5Z0DEiLjeLp9PrK27R6J+n8NzsYy3Axtvl8niVDHWG7vEh BRfiRXANFxQT7Efa6IOj/5wlTjUziYMA5K6fFqAtioFqNQReh+y/4bjENnJy5h2V6QP5 8FjpWenUluP6NhV1yJcIZw1oxe0zBNtFgSEgscypBqDe8DumtVzqN+rZhWIr+3Gvjtto zXmC/CcVNVGulGpWNvaZS1lYRlENojUc+f5z5nBwyS/hUT8Q7VLs427feIceMCQ+kZW1 d7aA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=l0u5WHmdUM6QOorSCuU0hXeCuOESdwfl8W0or7sC/p0=; b=rVbfbRnPY91+1U6ArwOKB7p3rSBvXjkRWBWwRGSujyHSDOz9Z0Uf1Tup4HAl+0aF8C eNG6QPJyEFrOgBlr46cde4mM9lUR2SemDVo21KlQ38FA1CAuD7FL3+9FPE3t73+qWJv0 jqkCXQlXrsan0oPDEkZNuxZU1o86/z9tvq3qle9fXRmH35eG8Eem22ueYgfV6+b9BD83 asnDOBajilwtLPatFkyNqWoeXLgM5DwwriJJQU6acwYO+m4Zn/9jsJ8+W09HtFOesQT1 buM1PtElP4bkisnLQkLspU26cghQAQ/E2akd1h1BpSssNVsqLC9ZY36olwKtUvgUTSwI Fdzg== X-Gm-Message-State: APjAAAXCym3nXc5MstUE5jKmNlPsK0ZR3B055VUyN2zBSIiN1fp//7GF jtPB5OHyV1NW6YWeTfI6pX5qlrpu+8k= X-Google-Smtp-Source: APXvYqxKw+UDSzFPorj7gQLjp60qCAQLfwlLORGcNaod/wqAnoKknk0JoX4ZoTzkswj9Cu3BmvbE1Q== X-Received: by 2002:ac2:47ec:: with SMTP id b12mr5653974lfp.162.1580305282902; Wed, 29 Jan 2020 05:41:22 -0800 (PST) Received: from [172.31.190.83] ([86.57.146.226]) by smtp.gmail.com with ESMTPSA id a28sm975257ljn.75.2020.01.29.05.41.21 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 29 Jan 2020 05:41:22 -0800 (PST) Subject: Re: IORING_REGISTER_CREDS[_UPDATE]() and credfd_create()? To: Stefan Metzmacher , Jens Axboe Cc: io-uring , Linux API Mailing List References: <688e187a-75dd-89d9-921c-67de228605ce@samba.org> <1ac31828-e915-6180-cdb4-36685442ea75@kernel.dk> <0d4f43d8-a0c4-920b-5b8f-127c1c5a3fad@kernel.dk> <2d7e7fa2-e725-8beb-90b9-6476d48bdb33@gmail.com> <6c401e23-de7c-1fc1-4122-33d53fcf9700@kernel.dk> <35eebae7-76dd-52ee-58b2-4f9e85caee40@kernel.dk> <6e5ab6bf-6ff1-14df-1988-a80a7c6c9294@gmail.com> <2019e952-df2a-6b57-3571-73c525c5ba1a@kernel.dk> <0df4904f-780b-5d5f-8700-41df47a1b470@kernel.dk> <5406612e-299d-9d6e-96fc-c962eb93887f@gmail.com> <821243e7-b470-ad7a-c1a5-535bee58e76d@samba.org> From: Pavel Begunkov Message-ID: <9a419bc5-4445-318d-87aa-1474b49266dd@gmail.com> Date: Wed, 29 Jan 2020 16:41:18 +0300 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: <821243e7-b470-ad7a-c1a5-535bee58e76d@samba.org> 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 1/29/2020 4:11 PM, Stefan Metzmacher wrote: > Am 29.01.20 um 11:17 schrieb Pavel Begunkov: >> On 29/01/2020 03:54, Jens Axboe wrote: >>> On 1/28/20 5:24 PM, Jens Axboe wrote: >>>> On 1/28/20 5:21 PM, Pavel Begunkov wrote: >>>>> On 29/01/2020 03:20, Jens Axboe wrote: >>>>>> On 1/28/20 5:10 PM, Pavel Begunkov wrote: >>>>>>>>>> Checked out ("don't use static creds/mm assignments") >>>>>>>>>> >>>>>>>>>> 1. do we miscount cred refs? We grab one in get_current_cred() for each async >>>>>>>>>> request, but if (worker->creds != work->creds) it will never be put. >>>>>>>>> >>>>>>>>> Yeah I think you're right, that needs a bit of fixing up. >>>>>>>> >>>>>>> >>>>>>> Hmm, it seems it leaks it unconditionally, as it grabs in a ref in >>>>>>> override_creds(). >>>>>>> >>>>>> >>>>>> We grab one there, and an extra one. Then we drop one of them inline, >>>>>> and the other in __io_req_aux_free(). >>>>>> >>>>> Yeah, with the last patch it should make it even >>>> >>>> OK good we agree on that. I should probably pull back that bit to the >>>> original patch to avoid having a hole in there... >>> >>> Done >>> >> >> ("io_uring/io-wq: don't use static creds/mm assignments") and ("io_uring: >> support using a registered personality for commands") looks good now. >> >> Reviewed-by: Pavel Begunkov > > > I'm very happy with the design, thanks! > That exactly what I had in mind:-) > > It would also work with IORING_SETUP_SQPOLL, correct? > Yep > However I think there're a few things to improve/simplify. > Since 5.6 is already semi-open, it'd be great to have an incremental patch for that. I'll retoss things as usual, if nobody do it before. >> https://git.kernel.dk/cgit/linux-block/commit/?h=for-5.6/io_uring-vfs&id=a26d26412e1e1783473f9dc8f030c3af3d54b1a6 > > In fs/io_uring.c mmgrab() and get_current_cred() are used together in > two places, why is put_cred() called in __io_req_aux_free while > mmdrop() is called from io_put_work(). I think both should be called > in io_put_work(), that makes the code much easier to understand. > > My guess is that you choose __io_req_aux_free() for put_cred() because > of the following patches, but I'll explain on the other commit > why it's not needed. > >> https://git.kernel.dk/cgit/linux-block/commit/?h=for-5.6/io_uring-vfs&id=d9db233adf034bd7855ba06190525e10a05868be > > A minor one would be starting with 1 instead of 0 and using > idr_alloc_cyclic() in order to avoid immediate reuse of ids. > That way we could include the id in the tracing message and > 0 would mean the current creds were used. > >> +static int io_remove_personalities(int id, void *p, void *data) >> +{ >> + struct io_ring_ctx *ctx = data; >> + >> + idr_remove(&ctx->personality_idr, id); > > Here we need something like: > put_creds((const struct cred *)p); Good catch > >> + return 0; >> +} > > > The io_uring_register() calles would look like this, correct? > > id = io_uring_register(ring_fd, IORING_REGISTER_PERSONALITY, NULL, 0); > io_uring_register(ring_fd, IORING_UNREGISTER_PERSONALITY, NULL, id); > >> https://git.kernel.dk/cgit/linux-block/commit/?h=for-5.6/io_uring-vfs&id=eec9e69e0ad9ad364e1b6a5dfc52ad576afee235 >> + >> + if (sqe_flags & IOSQE_PERSONALITY) { >> + int id = READ_ONCE(sqe->personality); >> + >> + req->work.creds = idr_find(&ctx->personality_idr, id); >> + if (unlikely(!req->work.creds)) { >> + ret = -EINVAL; >> + goto err_req; >> + } >> + get_cred(req->work.creds);> + old_creds = override_creds(req->work.creds); >> + } >> + > > Here we could use a helper variable > const struct cred *personality_creds; > and leave req->work.creds as NULL. > It means we can avoid the explicit get_cred() call > and can skip the following hunk too: > >> @@ -3977,7 +3977,8 @@ static int io_req_defer_prep(struct io_kiocb *req, >> mmgrab(current->mm); >> req->work.mm = current->mm; >> } >> - req->work.creds = get_current_cred(); >> + if (!req->work.creds) >> + req->work.creds = get_current_cred(); >> >> switch (req->opcode) { >> case IORING_OP_NOP: > > The override_creds(personality_creds) has changed current->cred > and get_current_cred() will just pick it up as in the default case. > > This would make the patch much simpler and allows put_cred() to be > in io_put_work() instead of __io_req_aux_free() as explained above. > It's one extra get_current_cred(). I'd prefer to find another way to clean this up. -- Pavel Begunkov