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 70BB4C4332B for ; Fri, 20 Mar 2020 13:27:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3B8F22076E for ; Fri, 20 Mar 2020 13:27:14 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="AOugaLk+" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727152AbgCTN1O (ORCPT ); Fri, 20 Mar 2020 09:27:14 -0400 Received: from us-smtp-delivery-74.mimecast.com ([63.128.21.74]:24251 "EHLO us-smtp-delivery-74.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727135AbgCTN1N (ORCPT ); Fri, 20 Mar 2020 09:27:13 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1584710832; 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=POqaw/FzEI0CTYjogTPDNEyESdDoII+GoAasJ6PFXJc=; b=AOugaLk+fvsm+Sh9/dYT7edGGoj/cEp/jrnYM09hLAKYKclgj2+lesXiWuFd38bIWmyN+N n3wrQ+HaKuddTlxbA7cEw1AzWWZiEwrWvyGID07ldVMF/bSdKeIuLLs76zDF5JPjRRzora RxA2EjtfJFTah2IA+lmds30J3AOz/kQ= 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-370-wfUqiJITPG6-L5EefAJGvA-1; Fri, 20 Mar 2020 09:27:10 -0400 X-MC-Unique: wfUqiJITPG6-L5EefAJGvA-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id E2697477; Fri, 20 Mar 2020 13:27:07 +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 E3F4660BFB; Fri, 20 Mar 2020 13:27:03 +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> From: Waiman Long Organization: Red Hat Message-ID: <7dbc524f-6c16-026a-a372-2e80b40eab30@redhat.com> Date: Fri, 20 Mar 2020 09:27:03 -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: <20200320020717.GC183331@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 10.5.11.12 Sender: linux-integrity-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-integrity@vger.kernel.org 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. Cheers, Longman