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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,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 21724C2B9F4 for ; Mon, 14 Jun 2021 17:03:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0779061246 for ; Mon, 14 Jun 2021 17:03:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235342AbhFNRFy (ORCPT ); Mon, 14 Jun 2021 13:05:54 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34182 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235074AbhFNRFw (ORCPT ); Mon, 14 Jun 2021 13:05:52 -0400 Received: from zeniv-ca.linux.org.uk (zeniv-ca.linux.org.uk [IPv6:2607:5300:60:148a::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E39F3C061574 for ; Mon, 14 Jun 2021 10:03:49 -0700 (PDT) Received: from viro by zeniv-ca.linux.org.uk with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1lspzw-0089t0-Fc; Mon, 14 Jun 2021 17:03:40 +0000 Date: Mon, 14 Jun 2021 17:03:40 +0000 From: Al Viro To: Jhih Ming Huang Cc: Greg KH , fabioaiuto83@gmail.com, ross.schm.dev@gmail.com, maqianga@uniontech.com, marcocesati@gmail.com, linux-staging@lists.linux.dev, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] rtw_security: fix cast to restricted __le32 Message-ID: References: <20210613122858.1433252-1-fbihjmeric@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: Al Viro Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jun 14, 2021 at 11:27:03PM +0800, Jhih Ming Huang wrote: > Thanks for your explanation. > > To clarify, even though it might be false positives in some senses, > following "hold the variable native-endian and check the conversion > done correctly" > is much easier than the other way. And it's exactly the current implementation. > > So it's better to keep the current implementation and ignore the > warnings, right? Umm... If that's the case, the warnings should go away if you use cpu_to_le32() for conversions from native to l-e and le32_to_cpu() for conversions from l-e to native. IOW, the choice between those should annotate what's going on. In your case doing *((u32 *)crc) = le32_to_cpu((__force __le32)~crc32_le(~0, payload, length - 4)); is wrong - you have crc32_le(...) native-endian ~crc32_le(...) - ditto le32_to_cpu(~crc32_le(...)) - byteswapped native-endian on b-e, unchanged on l-e. So result will be little-endian representation of ~crc32(...) in all cases. IOW, it's cpu_to_le32(~crc32_le(...)), misannotated as native-endian instead of little-endian it actually is. Then you store that value (actually __le32) into *(u32 *)crc. Seeing that crc is u8[4] there, that *(u32 *) is misleading - you are actually storing __le32 there (and, AFAICS, doing noting with the result). The same story in rtw_tkip_decrypt(), only there you do use the result later. So just make it __le32 crc and crc = cpu_to_le32(~crc32_le(~0, payload, length - 4)); with if (crc[3] != payload[length - 1] || crc[2] != payload[length - 2] || crc[1] != payload[length - 3] || crc[0] != payload[length - 4]) turned into if (memcmp(&crc, payload + length - 4, 4) != 0) (or (crc != get_unaligned((__le32 *)(payload + length - 4))), for that matter, to document what's going on and let the damn thing pick the optimal implementation for given architecture). Incidentally, your secmicgetuint32() is simply get_unaligned_le32() and secmicputuint32() - put_unaligned_le32(). No need to reinvent that wheel...