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=-11.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 E102CC3F68F for ; Fri, 14 Feb 2020 21:54:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B2D372082F for ; Fri, 14 Feb 2020 21:54:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581717298; bh=hYecJEDTMS4sRitWMiS4XFnCF5z2Aq11PjB0ocf5FBA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=HW13/lbyOyBcE1qfULXJFqJYpLZtQWqN5km/LVRmu5vKiRtgDPXi0tx0bP2B05cuA efguoqksMW6F/e3w/PzX3rB5CHZnZkdHq0BBQkc2CGa8PbpTj8HP/hS4TA4qACJdhU +75i7X1Hotcr2kwvuhdsQUR8r8LDA6Iq8zZifiuM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387865AbgBNVyh (ORCPT ); Fri, 14 Feb 2020 16:54:37 -0500 Received: from mail.kernel.org ([198.145.29.99]:59546 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387666AbgBNVyd (ORCPT ); Fri, 14 Feb 2020 16:54:33 -0500 Received: from localhost (unknown [65.119.211.164]) (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 0823B2168B; Fri, 14 Feb 2020 21:54:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581717273; bh=hYecJEDTMS4sRitWMiS4XFnCF5z2Aq11PjB0ocf5FBA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=efxubQc02cob0OZRWoak22UQRTd1ture8757Wvxpl1sJrxttz+uMoE1OapwO9G/CT rPdHFMetp53Bqm3kwxbnxS2qZXXQ3WMJAncji36qMySi33bKGv75PkcEo9jf6eRl2K p0mUjGuYet/enBHsH62vYCeNBn1zQ0HWcBivjdh8= Date: Fri, 14 Feb 2020 16:48:23 -0500 From: Greg Kroah-Hartman To: Sasha Levin Cc: linux-kernel@vger.kernel.org, stable@vger.kernel.org, "Gustavo A. R. Silva" Subject: Re: [PATCH AUTOSEL 5.5 456/542] char: hpet: Use flexible-array member Message-ID: <20200214214823.GD4193448@kroah.com> References: <20200214154854.6746-1-sashal@kernel.org> <20200214154854.6746-456-sashal@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200214154854.6746-456-sashal@kernel.org> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Feb 14, 2020 at 10:47:28AM -0500, Sasha Levin wrote: > From: "Gustavo A. R. Silva" > > [ Upstream commit 987f028b8637cfa7658aa456ae73f8f21a7a7f6f ] > > Old code in the kernel uses 1-byte and 0-byte arrays to indicate the > presence of a "variable length array": > > struct something { > int length; > u8 data[1]; > }; > > struct something *instance; > > instance = kmalloc(sizeof(*instance) + size, GFP_KERNEL); > instance->length = size; > memcpy(instance->data, source, size); > > There is also 0-byte arrays. Both cases pose confusion for things like > sizeof(), CONFIG_FORTIFY_SOURCE, etc.[1] Instead, the preferred mechanism > to declare variable-length types such as the one above is a flexible array > member[2] which need to be the last member of a structure and empty-sized: > > struct something { > int stuff; > u8 data[]; > }; > > Also, 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 > unadvertenly introduced[3] to the codebase from now on. > > [1] https://github.com/KSPP/linux/issues/21 > [2] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html > [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") > > Signed-off-by: Gustavo A. R. Silva > Link: https://lore.kernel.org/r/20200120235326.GA29231@embeddedor.com > Signed-off-by: Greg Kroah-Hartman > Signed-off-by: Sasha Levin > --- > drivers/char/hpet.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/char/hpet.c b/drivers/char/hpet.c > index 9ac6671bb5141..aed2c45f7968c 100644 > --- a/drivers/char/hpet.c > +++ b/drivers/char/hpet.c > @@ -110,7 +110,7 @@ struct hpets { > unsigned long hp_delta; > unsigned int hp_ntimer; > unsigned int hp_which; > - struct hpet_dev hp_dev[1]; > + struct hpet_dev hp_dev[]; > }; > > static struct hpets *hpets; > -- > 2.20.1 > Not needed, please drop from all trees. Along with the other hpet patch that fixes the bug this one introduced :) thanks, greg k-h