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=-13.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 45044C3F68F for ; Fri, 14 Feb 2020 23:36:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1D49C217F4 for ; Fri, 14 Feb 2020 23:36:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581723414; bh=CQufoR7vHijqQ6Q1/0cEdB0Ync1D9nO2IZkeI2H75Sc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=CQ1KE8z6qpZ1MGjNFz0xArSH4iGn7nfq0IiOmVXUBhq9OnAr20Gyfv8ys12fBVTjw 7VP2GVYZO6gyh1Pi3DUuM1HG9Wl6/odWG8MvXy6YJZOm9Am+bVxA/PeDnoByCN5gGd mbapBZdb1Yoi0yhxJbdg7rfpa710ixrSeAAT+iao= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728062AbgBNXgx (ORCPT ); Fri, 14 Feb 2020 18:36:53 -0500 Received: from mail.kernel.org ([198.145.29.99]:58560 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727529AbgBNXgx (ORCPT ); Fri, 14 Feb 2020 18:36:53 -0500 Received: from localhost (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (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 072F620848; Fri, 14 Feb 2020 23:36:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581723412; bh=CQufoR7vHijqQ6Q1/0cEdB0Ync1D9nO2IZkeI2H75Sc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=yrgmy2q8EpweD7RUkFgiP8HX+Qp1QWR8CzgtZf5aGrXo1Vdar0+Idl9I1sraSBoWV tjuBzFH0WwkRBq9QqLyUV8ngZhQxffr3nY1hqpgeQkh0SaQGwFw2dOqFmGxC2B2efv OXZZdEqJhCLqWa3xB2PDpmEw8YE3nz1+/r0FUj+8= Date: Fri, 14 Feb 2020 18:36:50 -0500 From: Sasha Levin To: Eric Biggers Cc: linux-kernel@vger.kernel.org, stable@vger.kernel.org, "Gustavo A. R. Silva" , Greg Kroah-Hartman Subject: Re: [PATCH AUTOSEL 4.4 080/100] char: hpet: Use flexible-array member Message-ID: <20200214233650.GF1734@sasha-vm> References: <20200214162425.21071-1-sashal@kernel.org> <20200214162425.21071-80-sashal@kernel.org> <20200214174314.GA250980@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20200214174314.GA250980@gmail.com> User-Agent: Mutt/1.10.1 (2018-07-13) 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 09:43:14AM -0800, Eric Biggers wrote: >On Fri, Feb 14, 2020 at 11:24:04AM -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 5b38d7a8202a1..38c2ae93ce492 100644 >> --- a/drivers/char/hpet.c >> +++ b/drivers/char/hpet.c >> @@ -112,7 +112,7 @@ 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[]; >> }; >> > >Umm, why are you backporting this without the commit that fixes it? Does your mhm, for some reason it failed to apply to 4.19 and older. I can look at that. >AUTOSEL process really still not pay attention to Fixes tags? They are there >for a reason. Yes, it looks at the Fixes tag, thank you for the explanation. >And for that matter, why are you backporting it all, given that this is a >cleanup and not a fix? If I recall correctly CONFIG_FORTIFY_SOURCE=y results in user visible warnings, which we try to fix in the stable kernel. -- Thanks, Sasha