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=-0.8 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, 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 7F1E9C2BA83 for ; Wed, 12 Feb 2020 06:34:56 +0000 (UTC) Received: from lists.sourceforge.net (lists.sourceforge.net [216.105.38.7]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 4E9CA206DB for ; Wed, 12 Feb 2020 06:34:56 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=sourceforge.net header.i=@sourceforge.net header.b="IQXwc/Z9"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=sf.net header.i=@sf.net header.b="L4TJL+/X"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="d4g4lNmp" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4E9CA206DB Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linux-f2fs-devel-bounces@lists.sourceforge.net Received: from [127.0.0.1] (helo=sfs-ml-2.v29.lw.sourceforge.com) by sfs-ml-2.v29.lw.sourceforge.com with esmtp (Exim 4.90_1) (envelope-from ) id 1j1lbr-0007yA-Rz; Wed, 12 Feb 2020 06:34:55 +0000 Received: from [172.30.20.202] (helo=mx.sourceforge.net) by sfs-ml-2.v29.lw.sourceforge.com with esmtps (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.90_1) (envelope-from ) id 1j1lbq-0007y2-D8 for linux-f2fs-devel@lists.sourceforge.net; Wed, 12 Feb 2020 06:34:54 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=sourceforge.net; s=x; h=In-Reply-To:Content-Type:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To:Content-Transfer-Encoding: Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender: Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help:List-Unsubscribe: List-Subscribe:List-Post:List-Owner:List-Archive; bh=fjO3CKjzgbhDec3VmE/h7cQTzvhn7qgldujhYbFENeU=; b=IQXwc/Z9S2OSaEo7OJNHSc4IcA ATIJyJVN4NtL6p7CxfuNOFV1EA/dIvwR1UniZevpkjdA2uyDAZmv0PgAbSgpzo05xS/PWue+IjMYR U8MrSrIxhkhIyeYJGcyiucbh6BLBwg5cwFVcCPSsxwx5V8EBeb7b3YAY1e4pIMJsY7Xo=; DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=sf.net; s=x ; h=In-Reply-To:Content-Type:MIME-Version:References:Message-ID:Subject:Cc:To :From:Date:Sender:Reply-To:Content-Transfer-Encoding:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Id:List-Help:List-Unsubscribe:List-Subscribe: List-Post:List-Owner:List-Archive; bh=fjO3CKjzgbhDec3VmE/h7cQTzvhn7qgldujhYbFENeU=; b=L4TJL+/XA8+icg1EZ0wAlsOCwO 0/E4T/PP7pXkTFeREMRfpcPmpgPVrGNk45jKlpOvxLDxOOTizgMpGrot16If9XlNYHk900hXDlGWS MD7tsACfSvAVXnl+cLTdXePL2E0PRkZ1o9kn0uHzmA5J1du0tS7+54kG1rI0Gw5m0baQ=; Received: from mail.kernel.org ([198.145.29.99]) by sfi-mx-1.v28.lw.sourceforge.com with esmtps (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.92.2) id 1j1lbk-009JA9-F4 for linux-f2fs-devel@lists.sourceforge.net; Wed, 12 Feb 2020 06:34:54 +0000 Received: from sol.localdomain (c-107-3-166-239.hsd1.ca.comcast.net [107.3.166.239]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 53335206DB; Wed, 12 Feb 2020 06:34:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581489282; bh=CzRudUeDo+wVwa7/TNw7sOyO0DwUDMqITe6/PlMG8AQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=d4g4lNmp0zgUEvD5Jg1HZ/pSYEOYUwWzEbd72XucSsanE7PW6E7KaMoizocCC9c/t fLsIxOWqbCUmHAYQrB/RRoUcW3yXF6qgwvTwkbZNe8+cBgUnJcRi5dGGEeKdxlXsX9 ZfevMBE0eHrc3SnIROac5ZH1k6H9MTGLrsW4OB+M= Date: Tue, 11 Feb 2020 22:34:40 -0800 From: Eric Biggers To: Al Viro Message-ID: <20200212063440.GL870@sol.localdomain> References: <20200208013552.241832-1-drosen@google.com> <20200208013552.241832-3-drosen@google.com> <20200208021216.GE23230@ZenIV.linux.org.uk> <20200210234207.GJ23230@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200210234207.GJ23230@ZenIV.linux.org.uk> X-Headers-End: 1j1lbk-009JA9-F4 Subject: Re: [f2fs-dev] [PATCH v7 2/8] fs: Add standard casefolding support X-BeenThere: linux-f2fs-devel@lists.sourceforge.net X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kernel-team@android.com, Theodore Ts'o , Daniel Rosenberg , Jonathan Corbet , Richard Weinberger , Andreas Dilger , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-fscrypt@vger.kernel.org, linux-mtd@lists.infradead.org, linux-fsdevel@vger.kernel.org, Jaegeuk Kim , linux-ext4@vger.kernel.org, Gabriel Krisman Bertazi Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: linux-f2fs-devel-bounces@lists.sourceforge.net On Mon, Feb 10, 2020 at 11:42:07PM +0000, Al Viro wrote: > On Mon, Feb 10, 2020 at 03:11:13PM -0800, Daniel Rosenberg wrote: > > On Fri, Feb 7, 2020 at 6:12 PM Al Viro wrote: > > > > > > On Fri, Feb 07, 2020 at 05:35:46PM -0800, Daniel Rosenberg wrote: > > > > > > > > > Again, is that safe in case when the contents of the string str points to > > > keeps changing under you? > > > > I'm not sure what you mean. I thought it was safe to use the str and > > len passed into d_compare. Even if it gets changed under RCU > > conditions I thought there was some code to ensure that the name/len > > pair passed in is consistent, and any other inconsistencies would get > > caught by d_seq later. Are there unsafe code paths that can follow? > > If you ever fetch the same byte twice, you might see different values. > You need a fairly careful use of READ_ONCE() or equivalents to make > sure that you don't get screwed over by that. > > Sure, ->d_seq mismatch will throw the result out, but you need to make > sure you won't oops/step on uninitialized memory/etc. in process. > > It's not impossible to get right, but it's not trivial and you need all > code working with that much more careful than normal for string handling. It looks like this is a real problem, not just a "theoretical" data race. For example, see: utf8ncursor(): /* The first byte of s may not be an utf8 continuation. */ if (len > 0 && (*s & 0xC0) == 0x80) return -1; and then utf8byte(): } else if ((*u8c->s & 0xC0) == 0x80) { /* This is a continuation of the current character. */ if (!u8c->p) u8c->len--; return (unsigned char)*u8c->s++; The first byte of the string is checked in two different functions, so it's very likely to be loaded twice. In between, it could change from a non-continuation byte to a continuation byte. That would cause the string length to be decremented from 0 to UINT_MAX. Then utf8_strncasecmp() would run beyond the bounds of the string until something happened to mismatch. That's just an example that I found right away; there are probably more. IMO, this needs to be fixed before anyone can actually use the ext4 and f2fs casefolding stuff. I don't know the best solution. One option is to fix fs/unicode/ to handle concurrently modified strings. Another could be to see what it would take to serialize lookups and renames for casefolded directories... - Eric _______________________________________________ Linux-f2fs-devel mailing list Linux-f2fs-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel