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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 D218AC28CF8 for ; Sat, 13 Oct 2018 09:04:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8E88420835 for ; Sat, 13 Oct 2018 09:04:49 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8E88420835 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ZenIV.linux.org.uk 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 S1726827AbeJMQlJ (ORCPT ); Sat, 13 Oct 2018 12:41:09 -0400 Received: from zeniv.linux.org.uk ([195.92.253.2]:48870 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726123AbeJMQlJ (ORCPT ); Sat, 13 Oct 2018 12:41:09 -0400 Received: from viro by ZenIV.linux.org.uk with local (Exim 4.90_1 #2 (Red Hat Linux)) id 1gBFqa-0006TX-Vq; Sat, 13 Oct 2018 09:04:33 +0000 Date: Sat, 13 Oct 2018 10:04:32 +0100 From: Al Viro To: Aleksa Sarai Cc: Aleksa Sarai , Jann Horn , "Eric W. Biederman" , jlayton@kernel.org, Bruce Fields , Arnd Bergmann , Andy Lutomirski , David Howells , christian@brauner.io, Tycho Andersen , David Drysdale , dev@opencontainers.org, containers@lists.linux-foundation.org, linux-fsdevel@vger.kernel.org, kernel list , linux-arch , Linux API Subject: Re: [PATCH v3 3/3] namei: aggressively check for nd->root escape on ".." resolution Message-ID: <20181013090432.GV32577@ZenIV.linux.org.uk> References: <20181009070230.12884-1-cyphar@cyphar.com> <20181009070230.12884-4-cyphar@cyphar.com> <20181009153728.2altaqxclntvyc7b@mikami> <20181013082210.GU32577@ZenIV.linux.org.uk> <20181013085326.gx6rvgqbbyuntfvv@ryuk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181013085326.gx6rvgqbbyuntfvv@ryuk> User-Agent: Mutt/1.9.1 (2017-09-22) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Oct 13, 2018 at 07:53:26PM +1100, Aleksa Sarai wrote: > I didn't know about path_is_under() -- I just checked and it appears to > not take &rename_lock? From my understanding, in order to protect > against the rename attack you need to take &rename_lock (or check > against &rename_lock at least and retry if it changed). > > I could definitely use path_is_under() if you prefer, though I think > that in this case we'd need to take &rename_lock (right?). Also is there > a speed issue with taking the write-side of a seqlock when we are just > reading -- is this more efficient than doing a retry like in __d_path? ??? 1) it uses is_subdir(), which does deal with rename_lock 2) what it does is taking mount_lock.lock. I.e. the same thing as the second retry in __d_path(). _If_ it shows up in profiles, we can switch it to read_seqbegin_or_lock(), but I'd like to see the profiling data first.