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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 45FA5C433F5 for ; Mon, 14 Feb 2022 17:16:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1357033AbiBNRQU convert rfc822-to-8bit (ORCPT ); Mon, 14 Feb 2022 12:16:20 -0500 Received: from mxb-00190b01.gslb.pphosted.com ([23.128.96.19]:46994 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1356970AbiBNRQS (ORCPT ); Mon, 14 Feb 2022 12:16:18 -0500 Received: from eu-smtp-delivery-151.mimecast.com (eu-smtp-delivery-151.mimecast.com [185.58.85.151]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id EFB47652C3 for ; Mon, 14 Feb 2022 09:16:09 -0800 (PST) Received: from AcuMS.aculab.com (156.67.243.121 [156.67.243.121]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384) id uk-mta-196-yVufUhzxMf6aRMAEmkShMQ-1; Mon, 14 Feb 2022 17:16:07 +0000 X-MC-Unique: yVufUhzxMf6aRMAEmkShMQ-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) by AcuMS.aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) with Microsoft SMTP Server (TLS) id 15.0.1497.28; Mon, 14 Feb 2022 17:16:06 +0000 Received: from AcuMS.Aculab.com ([fe80::994c:f5c2:35d6:9b65]) by AcuMS.aculab.com ([fe80::994c:f5c2:35d6:9b65%12]) with mapi id 15.00.1497.028; Mon, 14 Feb 2022 17:16:06 +0000 From: David Laight To: 'Solar Designer' , "Eric W. Biederman" CC: "linux-kernel@vger.kernel.org" , "Alexey Gladkov" , Kees Cook , Shuah Khan , Christian Brauner , Ran Xiaokai , Michal Koutn?? , "stable@vger.kernel.org" Subject: RE: [PATCH 5/8] ucounts: Handle wrapping in is_ucounts_overlimit Thread-Topic: [PATCH 5/8] ucounts: Handle wrapping in is_ucounts_overlimit Thread-Index: AQHYIGEwFCfhAMi5WkKLr8caSZ9ypKyTSxMw Date: Mon, 14 Feb 2022 17:16:06 +0000 Message-ID: References: <87o83e2mbu.fsf@email.froward.int.ebiederm.org> <20220211021324.4116773-5-ebiederm@xmission.com> <20220212223638.GB29214@openwall.com> In-Reply-To: <20220212223638.GB29214@openwall.com> Accept-Language: en-GB, en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=C51A453 smtp.mailfrom=david.laight@aculab.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Solar Designer > Sent: 12 February 2022 22:37 ... > bool is_ucounts_overlimit(struct ucounts *ucounts, enum ucount_type type, unsigned long rlimit) > { > struct ucounts *iter; > long max = rlimit; > if (rlimit > LONG_MAX) > max = LONG_MAX; > > The assignment on "long max = rlimit;" would have already been UB if > "rlimit > LONG_MAX", which is only checked afterwards. I think the > above would be better written as: I'm pretty sure assignments and casts of negative values to unsigned types are actually well defined. Although the actual value may differ for ones-compliment and sign-overpunch systems. But I suspect Linux requires twos-compliment negative numbers. (In much the same way as it requires that NULL be the all zero bit pattern - although a load of annoying compiler warnings are only relevant if that isn't the case.) David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)