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=-0.6 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 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 CD375C432C0 for ; Tue, 3 Dec 2019 01:52:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A5584206DC for ; Tue, 3 Dec 2019 01:52:29 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="Xah07E77" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726350AbfLCBw0 (ORCPT ); Mon, 2 Dec 2019 20:52:26 -0500 Received: from mail-io1-f67.google.com ([209.85.166.67]:33967 "EHLO mail-io1-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726066AbfLCBw0 (ORCPT ); Mon, 2 Dec 2019 20:52:26 -0500 Received: by mail-io1-f67.google.com with SMTP id z193so1859356iof.1; Mon, 02 Dec 2019 17:52:25 -0800 (PST) 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=TxhmjFxB0fSH7WF0Z6dyOJrwDyDBweaa0/5KnNO4AIw=; b=Xah07E77EL/ykU6H/9fOr3zX6G7oIlWdMl7pW0DtOY4vE5v7mHQywBuRicQbOxpksI oVlMR+lFoPd7LKC19a9HB2/wy/+jDp1nqd76VCZFCXYDbcb0C0lFjdfWx07BFtI61NyQ ULUpd+qRbkc1lNFMKvsoL6LpvtelvqGIpA+TiKw+pssj6AYPYx8QilsR5BTdNjSgzXV4 TzOcqVnnTq03A9VJMHGxKZI9llFscQefkxFMrIAIJ8purFDg+fn3Sgw7mITq1bI0VNc4 ggGt0dKL3T+x/JX3njY7HBts2xJIycvxD925/sF8Btt8swkgBaabvykwCkAgzw+wuURe 7mSA== 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=TxhmjFxB0fSH7WF0Z6dyOJrwDyDBweaa0/5KnNO4AIw=; b=hU6FQJAWDthk/buOxzAm/mmxDjZ12pcNOatoFfO1OFMXT4sRKOU5BiLmjzDrpptUhi HIzseY1+gdmSy1NdmtVooRUYFfX4QRPKMNhK7Xi5H4JMufM8AeHTvMyu1/Qfcxa0qxUq Cr4zOyPyjQ9g2b7FPlk5t8sUn3b7TYAadjMBzhukwDJojB6tjLNwC81r5v0XFaa84uje nMHZJVc7ReqOxsUitYgrjwdLmvAXN0SaiFlsdKGfWwPd5KUJ1ZY21BoH0a7mbUhZmF5E ypHBHvP+lkTI2qoYTAarcHhelx4xGuR3IKTuEPfOSKzvL4+4JXyr01mtaFojCEhk4zL3 6k3A== X-Gm-Message-State: APjAAAXp4RK/6DGAd1ivw/hL1rRWrV89kMpM25mPaUzgVatIQBdz4MQJ Qz1wpl1hQsMCGbnAMxADpiDnc5+8UKUrtQesH7U= X-Google-Smtp-Source: APXvYqz/HtSAKmFvtGA3vewcbEqy6GpkXcTpGWeY7zvzD8UPDmBHZYqWa5qgMjPw9AT+xjcV03w5DfEQU74871jze0c= X-Received: by 2002:a02:a915:: with SMTP id n21mr3314772jam.117.1575337945183; Mon, 02 Dec 2019 17:52:25 -0800 (PST) MIME-Version: 1.0 References: <20191129142045.7215-1-agruenba@redhat.com> In-Reply-To: From: =?UTF-8?Q?Andreas_Gr=C3=BCnbacher?= Date: Tue, 3 Dec 2019 02:52:13 +0100 Message-ID: Subject: Re: [PATCH v2] fs: Fix page_mkwrite off-by-one errors To: Linus Torvalds Cc: Andreas Gruenbacher , Christoph Hellwig , "Darrick J. Wong" , Linux Kernel Mailing List , Alexander Viro , Jeff Layton , Sage Weil , Ilya Dryomov , "Theodore Ts'o" , Andreas Dilger , Jaegeuk Kim , Chao Yu , linux-xfs , linux-fsdevel , Richard Weinberger , Artem Bityutskiy , Adrian Hunter , Ceph Development , Ext4 Developers List , linux-f2fs-devel@lists.sourceforge.net, linux-mtd@lists.infradead.org, Chris Mason , Josef Bacik , David Sterba , linux-btrfs@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Sender: linux-xfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org Am Di., 3. Dez. 2019 um 02:09 Uhr schrieb Linus Torvalds : > > On Fri, Nov 29, 2019 at 6:21 AM Andreas Gruenbacher wrote: > > > > +/** > > + * page_mkwrite_check_truncate - check if page was truncated > > + * @page: the page to check > > + * @inode: the inode to check the page against > > + * > > + * Returns the number of bytes in the page up to EOF, > > + * or -EFAULT if the page was truncated. > > + */ > > +static inline int page_mkwrite_check_truncate(struct page *page, > > + struct inode *inode) > > +{ > > + loff_t size = i_size_read(inode); > > + pgoff_t end_index = (size + PAGE_SIZE - 1) >> PAGE_SHIFT; > > This special end_index calculation seems to be redundant. > > You later want "size >> PAGE_SHIFT" for another test, and that's > actually the important part. > > The "+ PAGE_SIZE - 1" case is purely to handle the "AT the page > boundary is special" case, but since you have to calculate > "offset_in_page(size)" anyway, that's entirely redundant - the answer > is part of that. > > So I think it would be better to write the logic as > > loff_t size = i_size_read(inode); > pgoff_t index = size >> PAGE_SHIFT; > int offset = offset_in_page(size); > > if (page->mapping != inode->i_mapping) > return -EFAULT; > > /* Page is wholly past the EOF page */ > if (page->index > index) > return -EFAULT; > /* page is wholly inside EOF */ > if (page->index < index) > return PAGE_SIZE; > /* bytes in a page? If 0, it's past EOF */ > return offset ? offset : -PAGE_SIZE; > > instead. That avoids the unnecessary "round up" part, and simply uses > the same EOF index for everything. And if we rearrange things slightly, we end up with: /* page is wholly inside EOF */ if (page->index < index) return PAGE_SIZE; /* page is wholly past EOF */ if (page->index > index || !offset) return -EFAULT; /* page is partially inside EOF */ return offset; Thanks, Andreas