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=-10.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FSL_HELO_FAKE,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 8EF29C35242 for ; Fri, 14 Feb 2020 23:47:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5F56F217F4 for ; Fri, 14 Feb 2020 23:47:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581724062; bh=Rqtm7Fu5SgzWDdiDN1MI1B+q475GFErOrffFo0i7x7M=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=cSDSig1q1NXFiqAAlUTby8MQtq5Jz5PFU+i5d0qUyuLN7bhTR1CoTv0LdcnR7U5E+ NUy9GO4D+55+ai1abKWgZr4xXvDDrrdEDjsmIrmmxS4AhusBHrVN224SIaPyCBAb6y ZIR8QXuIkBZVlSj3PfLXZW26aGLmBEh3/ylulUCw= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728404AbgBNXrm (ORCPT ); Fri, 14 Feb 2020 18:47:42 -0500 Received: from mail.kernel.org ([198.145.29.99]:34246 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728405AbgBNXrl (ORCPT ); Fri, 14 Feb 2020 18:47:41 -0500 Received: from gmail.com (unknown [104.132.1.77]) (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 C633720848; Fri, 14 Feb 2020 23:47:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581724061; bh=Rqtm7Fu5SgzWDdiDN1MI1B+q475GFErOrffFo0i7x7M=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=qV2UV5I9WQNUxXwgMQQUw4LUgdTsDqIOzNrYrVlR5/UZOudwgqo3t7B5TbNOwKKn+ 9tsHgyxs2B3ALAvZMmn1i2x6Zo1hODtZebIqIEoHp++0NP/SjgIknVBG5Q9o0TiKKY pP68FVYKrJYPwA91ifXJorXkWOZYhXURXbqC0QYY= Date: Fri, 14 Feb 2020 15:47:39 -0800 From: Eric Biggers To: Sasha Levin 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: <20200214234738.GB1985@gmail.com> References: <20200214162425.21071-1-sashal@kernel.org> <20200214162425.21071-80-sashal@kernel.org> <20200214174314.GA250980@gmail.com> <20200214233650.GF1734@sasha-vm> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200214233650.GF1734@sasha-vm> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On Fri, Feb 14, 2020 at 06:36:50PM -0500, Sasha Levin wrote: > 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. If there is commit A which is fixed by commit B, and commit A applies to the stable branch but commit B does not, then commit A shouldn't be backported without manually fixing commit B first -- since otherwise a known bug would be backported. You really need to be handling this as part of your AUTOSEL process. If it happened here, it has happened elsewhere too, given the hundreds/thousands of commits you're selecting for stable. - Eric