From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753220AbeDKOSG (ORCPT ); Wed, 11 Apr 2018 10:18:06 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:46627 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752852AbeDKOSE (ORCPT ); Wed, 11 Apr 2018 10:18:04 -0400 Subject: Re: [PATCH][next] afs: fix integer overflow when shifting 1 more than 32 places To: David Howells Cc: linux-afs@lists.infradead.org, kernel-janitors@vger.kernel.org, linux-kernel@vger.kernel.org References: <62e9abc2-b639-419c-afa7-e89054f7dce9@canonical.com> <20180411132613.18974-1-colin.king@canonical.com> <23535.1523453966@warthog.procyon.org.uk> <24493.1523455816@warthog.procyon.org.uk> From: Colin Ian King Openpgp: preference=signencrypt Autocrypt: addr=colin.king@canonical.com; prefer-encrypt=mutual; keydata= xsFNBE6TJCgBEACo6nMNvy06zNKj5tiwDsXXS+LhT+LwtEsy9EnraKYXAf2xwazcICSjX06e fanlyhB0figzQO0n/tP7BcfMVNG7n1+DC71mSyRK1ZERcG1523ajvdZOxbBCTvTitYOy3bjs +LXKqeVMhK3mRvdTjjmVpWnWqJ1LL+Hn12ysDVVfkbtuIm2NoaSEC8Ae8LSSyCMecd22d9Pn LR4UeFgrWEkQsqROq6ZDJT9pBLGe1ZS0pVGhkRyBP9GP65oPev39SmfAx9R92SYJygCy0pPv BMWKvEZS/7bpetPNx6l2xu9UvwoeEbpzUvH26PHO3DDAv0ynJugPCoxlGPVf3zcfGQxy3oty dNTWkP6Wh3Q85m+AlifgKZudjZLrO6c+fAw/jFu1UMjNuyhgShtFU7NvEzL3RqzFf9O1qM2m uj83IeFQ1FZ65QAiCdTa3npz1vHc7N4uEQBUxyXgXfCI+A5yDnjHwzU0Y3RYS52TA3nfa08y LGPLTf5wyAREkFYou20vh5vRvPASoXx6auVf1MuxokDShVhxLpryBnlKCobs4voxN54BUO7m zuERXN8kadsxGFzItAyfKYzEiJrpUB1yhm78AecDyiPlMjl99xXk0zs9lcKriaByVUv/NsyJ FQj/kmdxox3XHi9K29kopFszm1tFiDwCFr/xumbZcMY17Yi2bQARAQABzSJDb2xpbiBLaW5n IDxjb2xpbi5raW5nQHVidW50dS5jb20+wsF3BBMBCAAhBQJPCrjvAhsDBQsJCAcDBRUKCQgL BRYCAwEAAh4BAheAAAoJEGjCh9/GqAImjVsP/iA8hDQy7LlMYepND9tKJD2haNLmsBC+yuxX BybYprtSjwvMbx6CtmtiJ4nGfdBzbZv3xOJPr/n6wxrdfGHEFn0W8Au97Xvk087P7alCwBXz y1Hk1aTlhLOGunOLv6SWRYRUAHvWEoVlxPSo2UNJ6D01d9tc7IJU08MlAl+u048S6625G5SG tfOJpFyGqaWGazMpkYdbJuY9acNAQAl1GzZPDCyLrxaBJypqmp3W+rb7m9arNRMlygevFU6e UGrR7QiVuumTGebGF9D63H9LD0E/1EhOA4QWHq1/u7CXLr9qo1YyAUtYAICs0wyRbI6wWPyi 5IyOTiWCVP3qSxV4JR8qq8JhGEwxS5fEB76r+XGxcL7qqiQmVx3bkjlT6FnnanPcD7RsMOAg NcpeftVsqignFPA3XHaDeew4t99ef+wKwiiyU7jqduvSt8amLVip5dxN1TYKqWPauIHL3E2A KIKuqsZ9ftUJ3NXClAfI3EHPMYbok6b04nZSWmBttKHr8YkVF5b4jrabMLlVoCg+DGYffyDS YDwy9FPvJWkt6nffUXciearieSlHEt3f12CPp6OOR8yFZWlISYKdD9PDzXP9kJYTEWnr7dD3 feEZK+J9N5wpCU7HvfrA5HCOMJgf8Dcfscrj9H2Qp8vbErMP7jZ6OYapCOV5MZS6W57wlG2k zsFNBE6TJCgBEADF+hz+c0qF0R58DwiM8M/PopzFu5ietBpl0jUzglaKhMZKKW7lAr4pzeE4 PgJ4ZwQd0dSkx63hRqM963Fe35iXrreglpwZxgbbGluRJpoeoGWzuUpXE6Ze0A2nICFLk79a YHsFRwnKyol9M0AyZHCvBXi1HAdj17iXerCYN/ZILD5SO0dDiQl570/1Rp3d1z0l16DuCnK+ X3I7GT8Z9B3WAr6KCRiP0Grvopjxwkj4Z191mP/auf1qpWPXEAPLVAvu5oM7dlTIxX7dYa6f wlcm1uobZvmtXeDEuHJ3TkbFgRHrZwuh50GMLguG1QjhIPXlzE7/PBQszh5zGxPj8cR81txs 6K/0GGRnIrPhCIlOoTU8L+BenxZF31uutdScHw1EAgB6AsRdwdd8a9AR+XdhHGzQel8kGyBp 4MA7508ih0L9+MBPuCrSsccjwV9+mfsTszrbZosIhVpBaeHNrUMphwFe9HbGUwQeS6tOr+py bOtNUHeiJ5aU3Npo3eZkWVGePP2O4vr8rjVQ1xZMIWA18xUaLTvVSarV7/IqjLb0uMTz6Ng7 SceqjsgxO4J35pPOCG8gy85Tmd5NKe46K1xGsNG2zzfXQ6cNkofUyQFGVbLCtdfQyWV7+dgU nOnPhrTKpFfJ5lnWpLpze0LfyW03CpWx9x4yMlwcvIFw2hLaOQARAQABwsFfBBgBCAAJBQJO kyQoAhsMAAoJEGjCh9/GqAImeJYP/jdppMeb7AZnLGVXd8rN7CLBtfMOkXCWaOUhjMRAY7dV IMiF1iPZc6SgiiMSsdG7JJhMjMuLTxA0kX2Z6P0+6dZlO4bDOKMIv4nNGhgSj9NuSKJPRiyi XKKD/wNnPXVFdBZsoHnEXGyAFGnidu4KLUJIiSm4tHJdoMk0ZaJSmwt0dtytuC1IWH8eIaVo /Ah6FxCaznRzvGNFx+9Ofcc7+aMZ15dkg9XagOuiDZ1/r6VuEw9ovnkDT4H5BAsysxo/qykX 4XQ2RQSY/P3td9WNLeXLvt1aJNRcwcIEKgZ5AO3YQbEJt1dEfCU7TAKiRpsjnC/iQiQHGt2I vNci8oZmM3EQEi7yZqD07A6dpGTnRq9OQ7fGhj0SS99yZvooH3fBIHA2LRuvhfDAgTrpbU0w LvkAIo0T2b9SoRCV8FEpHvR2b86NbTU5WN4eqZQbAbnxC7tJp6kLx2Zn2uQMvfXRfnS9R1ja etvpk3h7F+r/RAAh+EvgsPUNaiRJRRLvf9bxTQZhmNrw79eIFNsRIktniLyomJf2+WPOUECz h1lfLqe9yiuUKv+m5uAalXdayhiPbp/JHs1EDRgSq3tiirOsKrh/KMpwz/22qGMRBjFwYBhf 6ozgujmPlO5DVFtzfwOydzNlXTky7t4VU8yTGXZTJprIO+Gs72Q1e+XVIoKl3MIx Message-ID: <1b2c5c1b-0089-5790-6c3a-ff86645a5ec0@canonical.com> Date: Wed, 11 Apr 2018 15:17:59 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 MIME-Version: 1.0 In-Reply-To: <24493.1523455816@warthog.procyon.org.uk> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/04/18 15:10, David Howells wrote: > Colin Ian King wrote: > >>>> - mask = (1 << nr_slots) - 1; >>>> + mask = (1ULL << nr_slots) - 1; >>> >>> nr_slots cannot be larger than 9, so what I wrote is actually fine and is >>> more efficient on a 32-bit machine. >> >> ok, sorry about the noise. > > It would be possible to cast the value to u64 before assigning it, I suppose. > Would that help? E.g.: > > mask = (u64)((1 << nr_slots) - 1); > > It looks a bit odd, though, since the cast is made implicitly anyway. I'm not sure that actually helps, 1 << nr_slots is still evaluating as a 32 bit value, so that final cast does not may any difference. Anyhow, since nr_slots is less than 32 then keeping it the way it was is fine. > > David > -- > To unsubscribe from this list: send the line "unsubscribe kernel-janitors" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > From mboxrd@z Thu Jan 1 00:00:00 1970 From: Colin Ian King Date: Wed, 11 Apr 2018 14:17:59 +0000 Subject: Re: [PATCH][next] afs: fix integer overflow when shifting 1 more than 32 places Message-Id: <1b2c5c1b-0089-5790-6c3a-ff86645a5ec0@canonical.com> List-Id: References: <62e9abc2-b639-419c-afa7-e89054f7dce9@canonical.com> <20180411132613.18974-1-colin.king@canonical.com> <23535.1523453966@warthog.procyon.org.uk> <24493.1523455816@warthog.procyon.org.uk> In-Reply-To: <24493.1523455816@warthog.procyon.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: David Howells Cc: linux-afs@lists.infradead.org, kernel-janitors@vger.kernel.org, linux-kernel@vger.kernel.org On 11/04/18 15:10, David Howells wrote: > Colin Ian King wrote: > >>>> - mask = (1 << nr_slots) - 1; >>>> + mask = (1ULL << nr_slots) - 1; >>> >>> nr_slots cannot be larger than 9, so what I wrote is actually fine and is >>> more efficient on a 32-bit machine. >> >> ok, sorry about the noise. > > It would be possible to cast the value to u64 before assigning it, I suppose. > Would that help? E.g.: > > mask = (u64)((1 << nr_slots) - 1); > > It looks a bit odd, though, since the cast is made implicitly anyway. I'm not sure that actually helps, 1 << nr_slots is still evaluating as a 32 bit value, so that final cast does not may any difference. Anyhow, since nr_slots is less than 32 then keeping it the way it was is fine. > > David > -- > To unsubscribe from this list: send the line "unsubscribe kernel-janitors" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >