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=-3.8 required=3.0 tests=BAYES_00, 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 0A721C4320A for ; Tue, 31 Aug 2021 16:02:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E6ED460FE6 for ; Tue, 31 Aug 2021 16:02:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239482AbhHaQDA (ORCPT ); Tue, 31 Aug 2021 12:03:00 -0400 Received: from mail.kernel.org ([198.145.29.99]:39366 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232770AbhHaQC7 (ORCPT ); Tue, 31 Aug 2021 12:02:59 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id B0F4160F6B; Tue, 31 Aug 2021 16:02:01 +0000 (UTC) Date: Tue, 31 Aug 2021 17:01:58 +0100 From: Catalin Marinas To: Al Viro Cc: Linus Torvalds , Andreas Gruenbacher , Christoph Hellwig , "Darrick J. Wong" , Jan Kara , Matthew Wilcox , cluster-devel , linux-fsdevel , Linux Kernel Mailing List , "ocfs2-devel@oss.oracle.com" , Josef Bacik , Will Deacon Subject: Re: [RFC][arm64] possible infinite loop in btrfs search_ioctl() Message-ID: References: <20210827164926.1726765-6-agruenba@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Tue, Aug 31, 2021 at 03:28:57PM +0000, Al Viro wrote: > On Tue, Aug 31, 2021 at 02:54:50PM +0100, Catalin Marinas wrote: > > > An arm64-specific workaround would be for pagefault_disable() to disable > > tag checking. It's a pretty big hammer, weakening the out of bounds > > access detection of MTE. My preference would be a fix in the btrfs code. > > > > A btrfs option would be for copy_to_sk() to return an indication of > > where the fault occurred and get fault_in_pages_writeable() to check > > that location, even if the copying would restart from an earlier offset > > (this requires open-coding copy_to_user_nofault()). An attempt below, > > untested and does not cover read_extent_buffer_to_user_nofault(): > > Umm... There's another copy_to_user_nofault() call in the same function > (same story, AFAICS). Yeah, I was too lazy to do it all and I don't have a setup to test the patch quickly either. BTW, my hack is missing an access_ok() check. I wonder whether copy_{to,from}_user_nofault() could actually return the number of bytes left to copy, just like their non-nofault counterparts. These are only used in a few places, so fairly easy to change. If we go for a btrfs fix along the lines of my diff, it saves us from duplicating the copy_to_user_nofault() code. -- Catalin