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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham 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 47CE4C4646D for ; Mon, 6 Aug 2018 22:59:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F360E214FF for ; Mon, 6 Aug 2018 22:59:31 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org F360E214FF Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387652AbeHGBKr (ORCPT ); Mon, 6 Aug 2018 21:10:47 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:45780 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731200AbeHGBKr (ORCPT ); Mon, 6 Aug 2018 21:10:47 -0400 Received: from localhost.localdomain (c-24-4-125-7.hsd1.ca.comcast.net [24.4.125.7]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id D9F37EC3; Mon, 6 Aug 2018 22:59:28 +0000 (UTC) Date: Mon, 6 Aug 2018 15:59:27 -0700 From: Andrew Morton To: Jan Kara Cc: Chengguang Xu , mgorman@techsingularity.net, jlayton@redhat.com, ak@linux.intel.com, mawilcox@microsoft.com, tim.c.chen@linux.intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Al Viro Subject: Re: [PATCH] mm: adjust max read count in generic_file_buffered_read() Message-Id: <20180806155927.4740babd057df9d5078281b1@linux-foundation.org> In-Reply-To: <20180806102203.hmobd26cujmlfcsw@quack2.suse.cz> References: <20180719081726.3341-1-cgxu519@gmx.com> <20180719085812.sjup2odrjyuigt3l@quack2.suse.cz> <20180720161429.d63dccb9f66799dc0ff74dba@linux-foundation.org> <20180806102203.hmobd26cujmlfcsw@quack2.suse.cz> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 6 Aug 2018 12:22:03 +0200 Jan Kara wrote: > On Fri 20-07-18 16:14:29, Andrew Morton wrote: > > On Thu, 19 Jul 2018 10:58:12 +0200 Jan Kara wrote: > > > > > On Thu 19-07-18 16:17:26, Chengguang Xu wrote: > > > > When we try to truncate read count in generic_file_buffered_read(), > > > > should deliver (sb->s_maxbytes - offset) as maximum count not > > > > sb->s_maxbytes itself. > > > > > > > > Signed-off-by: Chengguang Xu > > > > > > Looks good to me. You can add: > > > > > > Reviewed-by: Jan Kara > > > > Yup. > > > > What are the runtime effects of this bug? > > Good question. I think ->readpage() could be called for index beyond > maximum file size supported by the filesystem leading to weird filesystem > behavior due to overflows in internal calculations. > Sure. But is it possible for userspace to trigger this behaviour? Possibly all callers have already sanitized the arguments by this stage in which case the statement is arguably redundant. I guess I'll put a cc:stable on it and send it in for 4.19-rc1, so we get a bit more time to poke at it. But we should have a better understanding of the userspace impact.