From mboxrd@z Thu Jan 1 00:00:00 1970 From: Waiman Long Date: Fri, 20 Mar 2020 15:09:32 +0000 Subject: Re: [PATCH v5 2/2] KEYS: Avoid false positive ENOMEM error on key read Message-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit List-Id: References: <20200318221457.1330-1-longman@redhat.com> <20200318221457.1330-3-longman@redhat.com> <20200319194650.GA24804@linux.intel.com> <20200320020717.GC183331@linux.intel.com> <7dbc524f-6c16-026a-a372-2e80b40eab30@redhat.com> <20200320143547.GB3629@linux.intel.com> In-Reply-To: <20200320143547.GB3629@linux.intel.com> To: Jarkko Sakkinen Cc: David Howells , James Morris , "Serge E. Hallyn" , Mimi Zohar , "David S. Miller" , Jakub Kicinski , keyrings@vger.kernel.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, linux-integrity@vger.kernel.org, netdev@vger.kernel.org, linux-afs@lists.infradead.org, Sumit Garg , Jerry Snitselaar , Roberto Sassu , Eric Biggers , Chris von Recklinghausen On 3/20/20 10:35 AM, Jarkko Sakkinen wrote: > On Fri, Mar 20, 2020 at 09:27:03AM -0400, Waiman Long wrote: >> On 3/19/20 10:07 PM, Jarkko Sakkinen wrote: >>> On Thu, Mar 19, 2020 at 08:07:55PM -0400, Waiman Long wrote: >>>> On 3/19/20 3:46 PM, Jarkko Sakkinen wrote: >>>>> On Wed, Mar 18, 2020 at 06:14:57PM -0400, Waiman Long wrote: >>>>>> + * It is possible, though unlikely, that the key >>>>>> + * changes in between the up_read->down_read period. >>>>>> + * If the key becomes longer, we will have to >>>>>> + * allocate a larger buffer and redo the key read >>>>>> + * again. >>>>>> + */ >>>>>> + if (!tmpbuf || unlikely(ret > tmpbuflen)) { >>>>> Shouldn't you check that tmpbuflen stays below buflen (why else >>>>> you had made copy of buflen otherwise)? >>>> The check above this thunk: >>>> >>>> if ((ret > 0) && (ret <= buflen)) { >>>> >>>> will make sure that ret will not be larger than buflen. So tmpbuflen > >> will never be bigger than buflen. > > Ah right, of course, thanks. >>> What would go wrong if the condition was instead >>> ((ret > 0) && (ret <= tmpbuflen))? >> That if statement is a check to see if the actual key length is longer >> than the user-supplied buffer (buflen). If that is the case, it will >> just return the expected length without storing anything into the user >> buffer. For the case that buflen >= ret > tmpbuflen, the revised check >> above will incorrectly skip the storing step causing the caller to >> incorrectly think the key is there in the buffer. >> >> Maybe I should clarify that a bit more in the comment. > OK, right because it is possible in-between tmpbuflen could be > larger. Got it. > > I think that longish key_data and key_data_len would be better > names than tmpbuf and tpmbuflen. > > Also the comments are somewat overkill IMHO. > > I'd replace them along the lines of > > /* Cap the user supplied buffer length to PAGE_SIZE. */ > > /* Key data can change as we don not hold key->sem. */ I am fine with the rename, will sent out a v6 soon. Cheers, Longman 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=-2.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 9B7A6C43332 for ; Fri, 20 Mar 2020 15:09:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 722E82072C for ; Fri, 20 Mar 2020 15:09:45 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="XiD+H/RX" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727144AbgCTPJo (ORCPT ); Fri, 20 Mar 2020 11:09:44 -0400 Received: from us-smtp-delivery-74.mimecast.com ([216.205.24.74]:29983 "EHLO us-smtp-delivery-74.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727148AbgCTPJn (ORCPT ); Fri, 20 Mar 2020 11:09:43 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1584716982; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=5+aUM1Yn2Y/IYb21uZgrRPO9zmI5FLmUctu7OcB3Czc=; b=XiD+H/RXSTTxQTYwdKnrIo8aDRuPzqrQ1c+6jR9qNwCVhu2JuIO0XoqNm095CLdAuDekZp gebchWus8myKinQ6dSPcihZBO8jvgWRGG1+U41DqTSLb6PyH6O65sRm8OolMR6rJcPvicL fa7tFowa6mZ1KJLAJRfucs2E1H18jL4= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-339-t2-NJVv6NAmkytbnxuHV-w-1; Fri, 20 Mar 2020 11:09:39 -0400 X-MC-Unique: t2-NJVv6NAmkytbnxuHV-w-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 354B018AB2C4; Fri, 20 Mar 2020 15:09:36 +0000 (UTC) Received: from llong.remote.csb (ovpn-118-190.rdu2.redhat.com [10.10.118.190]) by smtp.corp.redhat.com (Postfix) with ESMTP id ACDE25C1B8; Fri, 20 Mar 2020 15:09:32 +0000 (UTC) Subject: Re: [PATCH v5 2/2] KEYS: Avoid false positive ENOMEM error on key read To: Jarkko Sakkinen Cc: David Howells , James Morris , "Serge E. Hallyn" , Mimi Zohar , "David S. Miller" , Jakub Kicinski , keyrings@vger.kernel.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, linux-integrity@vger.kernel.org, netdev@vger.kernel.org, linux-afs@lists.infradead.org, Sumit Garg , Jerry Snitselaar , Roberto Sassu , Eric Biggers , Chris von Recklinghausen References: <20200318221457.1330-1-longman@redhat.com> <20200318221457.1330-3-longman@redhat.com> <20200319194650.GA24804@linux.intel.com> <20200320020717.GC183331@linux.intel.com> <7dbc524f-6c16-026a-a372-2e80b40eab30@redhat.com> <20200320143547.GB3629@linux.intel.com> From: Waiman Long Organization: Red Hat Message-ID: Date: Fri, 20 Mar 2020 11:09:32 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: <20200320143547.GB3629@linux.intel.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 3/20/20 10:35 AM, Jarkko Sakkinen wrote: > On Fri, Mar 20, 2020 at 09:27:03AM -0400, Waiman Long wrote: >> On 3/19/20 10:07 PM, Jarkko Sakkinen wrote: >>> On Thu, Mar 19, 2020 at 08:07:55PM -0400, Waiman Long wrote: >>>> On 3/19/20 3:46 PM, Jarkko Sakkinen wrote: >>>>> On Wed, Mar 18, 2020 at 06:14:57PM -0400, Waiman Long wrote: >>>>>> + * It is possible, though unlikely, that the key >>>>>> + * changes in between the up_read->down_read period. >>>>>> + * If the key becomes longer, we will have to >>>>>> + * allocate a larger buffer and redo the key read >>>>>> + * again. >>>>>> + */ >>>>>> + if (!tmpbuf || unlikely(ret > tmpbuflen)) { >>>>> Shouldn't you check that tmpbuflen stays below buflen (why else >>>>> you had made copy of buflen otherwise)? >>>> The check above this thunk: >>>> >>>> if ((ret > 0) && (ret <= buflen)) { >>>> >>>> will make sure that ret will not be larger than buflen. So tmpbuflen > >> will never be bigger than buflen. > > Ah right, of course, thanks. >>> What would go wrong if the condition was instead >>> ((ret > 0) && (ret <= tmpbuflen))? >> That if statement is a check to see if the actual key length is longer >> than the user-supplied buffer (buflen). If that is the case, it will >> just return the expected length without storing anything into the user >> buffer. For the case that buflen >= ret > tmpbuflen, the revised check >> above will incorrectly skip the storing step causing the caller to >> incorrectly think the key is there in the buffer. >> >> Maybe I should clarify that a bit more in the comment. > OK, right because it is possible in-between tmpbuflen could be > larger. Got it. > > I think that longish key_data and key_data_len would be better > names than tmpbuf and tpmbuflen. > > Also the comments are somewat overkill IMHO. > > I'd replace them along the lines of > > /* Cap the user supplied buffer length to PAGE_SIZE. */ > > /* Key data can change as we don not hold key->sem. */ I am fine with the rename, will sent out a v6 soon. Cheers, Longman