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=-2.7 required=3.0 tests=BAYES_00,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 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 A3DF8C433ED for ; Thu, 15 Apr 2021 07:14:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6BF3861103 for ; Thu, 15 Apr 2021 07:14:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231134AbhDOHOx (ORCPT ); Thu, 15 Apr 2021 03:14:53 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55250 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230201AbhDOHOw (ORCPT ); Thu, 15 Apr 2021 03:14:52 -0400 Received: from mail-yb1-xb34.google.com (mail-yb1-xb34.google.com [IPv6:2607:f8b0:4864:20::b34]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EA714C061574; Thu, 15 Apr 2021 00:14:29 -0700 (PDT) Received: by mail-yb1-xb34.google.com with SMTP id o10so25025738ybb.10; Thu, 15 Apr 2021 00:14:29 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=AmSJJ7fxEY1qfYfGbCGKBATmW67qLsXWzf2MAF6GFG8=; b=Oyp6JnSut4UGWs81Xjr/IfMcvKPiNWMRVJQsasx4yG0qjhOlEetIuSjXAe3PunijTt UXCdtiIBKpjBRHUb8rkQQ2xh172BOO1IBuYXxZsbzUAmsbQPxK2mckIijtoqEp8ylbZ8 D9ReIkKKfmC/Lbmg1GQt8nwXfNxzBstW2Y9v+nblLlPlOeOwAGLCR5i6dOGeRVS4ogDo iW1B4/DVJ7FsyV48cNcMrlqwfGi8uD1NI71GhfRrLB8Te4fBkLSxezacYGD7IEuDKkXv prZM9gMkfWugOHzq7W9UO9GT0X4qZSdLripEfSFjK765SzyAQ2FLXISNH8UuA3dOsYEd iOWw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=AmSJJ7fxEY1qfYfGbCGKBATmW67qLsXWzf2MAF6GFG8=; b=JH/K8k9Vhx5xWJhETmd8Udyeia+vCdxWDhdcg265gyNBG9R7ZrhBSz+H+ukkADYhJu Me5HYRDbx7SoqXzx/pzCP6AOq80QpBRdcDOXwIzMiHP66vLAdFDvh93DySTEh+QRdrrj SOVQydpAH/7E8iD7h0yzIv9HW7b4aNDQm8pE2HqcVV6FbOZ7GyAl8iKHIKI+5lTnZ07e BWvZrlmwG+fsZIu6HIhscrBwWmzr/14grRgS0qwF3ebhQIxSjmT+//5KxofYyz2MfRrE bBrGk4SsfL/b3WHKSsClegluiZJbCfFIfliBLmcTe2KImuy9ygTyqBM7EGgijITWYlrE lBHA== X-Gm-Message-State: AOAM533kuOQh7M7TzFsewQxVgHireonO5DAFfRR9DecK5Lg38RwmJpk7 pWSZKCNzT44yIlcInVNu6msqWsVGyI7HCDRtlBnk2KIfAj/DSaEH X-Google-Smtp-Source: ABdhPJy1A38856fQapXQ4ezTSfbE2TMGAWH2/Ef3BCDbt6+udhGvDCq4bLHxHdDymv1LLzPEHoNIKWQ4omQMeDAllM4= X-Received: by 2002:a25:cb57:: with SMTP id b84mr2431459ybg.167.1618470869088; Thu, 15 Apr 2021 00:14:29 -0700 (PDT) MIME-Version: 1.0 References: <20210330055957.3684579-1-dkadashev@gmail.com> <20210330055957.3684579-2-dkadashev@gmail.com> <20210330071700.kpjoyp5zlni7uejm@wittgenstein> In-Reply-To: From: Dmitry Kadashev Date: Thu, 15 Apr 2021 14:14:17 +0700 Message-ID: Subject: Re: [PATCH v3 1/2] fs: make do_mkdirat() take struct filename To: Christian Brauner Cc: Jens Axboe , Alexander Viro , Pavel Begunkov , linux-fsdevel@vger.kernel.org, io-uring Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On Thu, Apr 8, 2021 at 3:45 PM Dmitry Kadashev wrote: > > On Tue, Mar 30, 2021 at 2:17 PM Christian Brauner > wrote: > > The only thing that is a bit unpleasant here is that this change > > breaks the consistency between the creation helpers: > > > > do_mkdirat() > > do_symlinkat() > > do_linkat() > > do_mknodat() > > > > All but of them currently take > > const char __user *pathname > > and call > > user_path_create() > > with that do_mkdirat() change that's no longer true. One of the major > > benefits over the recent years in this code is naming and type consistency. > > And since it's just matter of time until io_uring will also gain support > > for do_{symlinkat,linkat,mknodat} I would think switching all of them to > > take a struct filename > > and then have all do_* helpers call getname() might just be nicer in the > > long run. > > So, I've finally got some time to look into this. do_mknodat() and > do_symlinkat() are easy. But do_linkat() is more complicated, I could use some > hints as to what's the reasonable way to implement the change. > > The problem is linkat() requires CAP_DAC_READ_SEARCH capability if AT_EMPTY_PATH > flag is passed. Right now do_linkat checks the capability before calling > getname_flags (essentially). If do_linkat is changed to accept struct filename > then there is no bulletproof way to force CAP_DAC_READ_SEARCH presence (e.g. if > for whatever reason AT_EMPTY_PATH is not in flags passed to do_linkat). Also, it > means that the caller is responsible to process AT_EMPTY_PATH in the first > place, which means logic duplication. > > Any ideas what's the best way to approach this? Ping. If someone can see how we can avoid making do_linkat() callers ensure the process has CAP_DAC_READ_SEARCH capability if AT_EMPTY_PATH was passed then the hints would be really appreciated. The best I could come up with is something like getname_linkat(), which could be used by the do_linkat callers, but this sounds error prone and ugly. Jens, do you want to keep the mkdir change out of 5.13 because of this? -- Dmitry Kadashev On Thu, Apr 8, 2021 at 3:45 PM Dmitry Kadashev wrote: > > On Tue, Mar 30, 2021 at 2:17 PM Christian Brauner > wrote: > > The only thing that is a bit unpleasant here is that this change > > breaks the consistency between the creation helpers: > > > > do_mkdirat() > > do_symlinkat() > > do_linkat() > > do_mknodat() > > > > All but of them currently take > > const char __user *pathname > > and call > > user_path_create() > > with that do_mkdirat() change that's no longer true. One of the major > > benefits over the recent years in this code is naming and type consistency. > > And since it's just matter of time until io_uring will also gain support > > for do_{symlinkat,linkat,mknodat} I would think switching all of them to > > take a struct filename > > and then have all do_* helpers call getname() might just be nicer in the > > long run. > > So, I've finally got some time to look into this. do_mknodat() and > do_symlinkat() are easy. But do_linkat() is more complicated, I could use some > hints as to what's the reasonable way to implement the change. > > The problem is linkat() requires CAP_DAC_READ_SEARCH capability if AT_EMPTY_PATH > flag is passed. Right now do_linkat checks the capability before calling > getname_flags (essentially). If do_linkat is changed to accept struct filename > then there is no bulletproof way to force CAP_DAC_READ_SEARCH presence (e.g. if > for whatever reason AT_EMPTY_PATH is not in flags passed to do_linkat). Also, it > means that the caller is responsible to process AT_EMPTY_PATH in the first > place, which means logic duplication. > > Any ideas what's the best way to approach this? > > Thanks. > > -- > Dmitry Kadashev