From patchwork Thu May 7 19:21:59 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Gustavo A. R. Silva" X-Patchwork-Id: 11534781 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 9703E92A for ; Thu, 7 May 2020 19:17:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7F162221F7 for ; Thu, 7 May 2020 19:17:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588879054; bh=TZeZW0+jfLlh4ZcEbv2LeoEqpPZMjTCgCitS0tjDun8=; h=Date:From:To:Cc:Subject:List-ID:From; b=yVeKQInjEGmhgsK8P3J6oo1uVnaBgqVpKPxS6mL5gWVqgbmZiQ8FJ7+xOE65PB48l 5Fjpjay9eUxmYJ6W04Hsxi0VNdnG9mn+RyAR1/ckP4MSTpG7MMI76Xcv+oGzq1IW8e 8z+7wEjh3DBPQgECVkROqX/IvE/fdhNfqMVQNycE= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728528AbgEGTRd (ORCPT ); Thu, 7 May 2020 15:17:33 -0400 Received: from mail.kernel.org ([198.145.29.99]:40536 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726367AbgEGTRd (ORCPT ); Thu, 7 May 2020 15:17:33 -0400 Received: from embeddedor (unknown [189.207.59.248]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 2C32A21835; Thu, 7 May 2020 19:17:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588879052; bh=TZeZW0+jfLlh4ZcEbv2LeoEqpPZMjTCgCitS0tjDun8=; h=Date:From:To:Cc:Subject:From; b=BOuwfW0y3gjqHMtue8yu0YfM2wr9KuUYdQ3Ijgzdyg0YG0Bh4kArsZPf/Q0JfZTnz j3qBjujXHQFDfHMYW9J1OghpLwKiwHEqdjhgBPEgWGP7xXMM09hKEkHO4ahQ5m8T01 CQmAzxBNFcoFdP5bbOLUAxk0NounFW1Qjqw3f4a4= Date: Thu, 7 May 2020 14:21:59 -0500 From: "Gustavo A. R. Silva" To: James Morris , "Serge E. Hallyn" Cc: linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] ima: Replace zero-length array with flexible-array Message-ID: <20200507192159.GA16250@embeddedor> MIME-Version: 1.0 Content-Disposition: inline User-Agent: Mutt/1.9.4 (2018-02-28) Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: The current codebase makes use of the zero-length array language extension to the C90 standard, but the preferred mechanism to declare variable-length types such as these ones is a flexible array member[1][2], introduced in C99: struct foo { int stuff; struct boo array[]; }; By making use of the mechanism above, we will get a compiler warning in case the flexible array does not occur last in the structure, which will help us prevent some kind of undefined behavior bugs from being inadvertently introduced[3] to the codebase from now on. Also, notice that, dynamic memory allocations won't be affected by this change: "Flexible array members have incomplete type, and so the sizeof operator may not be applied. As a quirk of the original implementation of zero-length arrays, sizeof evaluates to zero."[1] sizeof(flexible-array-member) triggers a warning because flexible array members have incomplete type[1]. There are some instances of code in which the sizeof operator is being incorrectly/erroneously applied to zero-length arrays and the result is zero. Such instances may be hiding some bugs. So, this work (flexible-array member conversions) will also help to get completely rid of those sorts of issues. This issue was found with the help of Coccinelle. [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html [2] https://github.com/KSPP/linux/issues/21 [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") Signed-off-by: Gustavo A. R. Silva --- security/integrity/integrity.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/security/integrity/integrity.h b/security/integrity/integrity.h index 298b73794d8b..16c1894c29bb 100644 --- a/security/integrity/integrity.h +++ b/security/integrity/integrity.h @@ -107,7 +107,7 @@ struct ima_digest_data { } ng; u8 data[2]; } xattr; - u8 digest[0]; + u8 digest[]; } __packed; /* @@ -119,7 +119,7 @@ struct signature_v2_hdr { uint8_t hash_algo; /* Digest algorithm [enum hash_algo] */ __be32 keyid; /* IMA key identifier - not X509/PGP specific */ __be16 sig_size; /* signature size */ - uint8_t sig[0]; /* signature payload */ + uint8_t sig[]; /* signature payload */ } __packed; /* integrity data associated with an inode */