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=-8.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,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 7B688C35242 for ; Fri, 14 Feb 2020 21:54:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4D34B2082F for ; Fri, 14 Feb 2020 21:54:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581717299; bh=ia4+nQ8WRA03MfSonkT9d7c8bMEztR6s5yKzyl1EbO4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=OOsLnUFl7TVgxASXFHoblXrqRYRjS5e1IUF7RF591xSLzBDSOnE9IZdbGOOOcyCAI hrlBt4Txi4I+SES3y8jdzBgyaGC1u8VebY86+5+QAl2VhBMZN+h+LI+kL9JIQVBiIN fgo2hf7nthf1gCc73mmcQw3IV1rQpXRGFS1cyxJs= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387870AbgBNVyh (ORCPT ); Fri, 14 Feb 2020 16:54:37 -0500 Received: from mail.kernel.org ([198.145.29.99]:59650 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387816AbgBNVyg (ORCPT ); Fri, 14 Feb 2020 16:54:36 -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 89ABC2081E; Fri, 14 Feb 2020 21:54:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581717275; bh=ia4+nQ8WRA03MfSonkT9d7c8bMEztR6s5yKzyl1EbO4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=SZHeKsvXMgrIUKjUJpQ0UCeB5pXbdeuwq6GwZ8fs8jL2xGr/3rlygof7h9lgcZJRR 0i0OiSwTjJj/JqvZHmnJMpGZmLKwY9jo942qx0eqGnnlFuGgZ0Fwiuhhl73pUHn8mv HV/BzoLrbU4DD1JDaTrBQniQewBd/KzK66DF94I8= Date: Fri, 14 Feb 2020 16:49:02 -0500 From: Greg Kroah-Hartman To: Sasha Levin Cc: linux-kernel@vger.kernel.org, stable@vger.kernel.org, "Gustavo A. R. Silva" , Jiri Slaby Subject: Re: [PATCH AUTOSEL 5.5 451/542] tty: n_hdlc: Use flexible-array member and struct_size() helper Message-ID: <20200214214902.GF4193448@kroah.com> References: <20200214154854.6746-1-sashal@kernel.org> <20200214154854.6746-451-sashal@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200214154854.6746-451-sashal@kernel.org> Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On Fri, Feb 14, 2020 at 10:47:23AM -0500, Sasha Levin wrote: > From: "Gustavo A. R. Silva" > > [ Upstream commit 85f4c95172d606dd66f7ee1fa50c45a245535ffd ] > > 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 > inadvertenly introduced[3] to the codebase from now on. > > Lastly, make use of the struct_size() helper to safely calculate the > allocation size for instances of struct n_hdlc_buf and avoid any potential > type mistakes[4][5]. > > [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") > [4] https://lore.kernel.org/lkml/60e14fb7-8596-e21c-f4be-546ce39e7bdb@embeddedor.com/ > [5] commit 553d66cb1e86 ("iommu/vt-d: Use struct_size() helper") > > Signed-off-by: Gustavo A. R. Silva > Reviewed-by: Jiri Slaby > Link: https://lore.kernel.org/r/20200121172138.GA3162@embeddedor > Signed-off-by: Greg Kroah-Hartman > Signed-off-by: Sasha Levin > --- > drivers/tty/n_hdlc.c | 11 +++++------ > 1 file changed, 5 insertions(+), 6 deletions(-) > > diff --git a/drivers/tty/n_hdlc.c b/drivers/tty/n_hdlc.c > index 98361acd3053f..27b506bf03ced 100644 > --- a/drivers/tty/n_hdlc.c > +++ b/drivers/tty/n_hdlc.c > @@ -115,11 +115,9 @@ > struct n_hdlc_buf { > struct list_head list_item; > int count; > - char buf[1]; > + char buf[]; > }; > > -#define N_HDLC_BUF_SIZE (sizeof(struct n_hdlc_buf) + maxframe) > - > struct n_hdlc_buf_list { > struct list_head list; > int count; > @@ -524,7 +522,8 @@ static void n_hdlc_tty_receive(struct tty_struct *tty, const __u8 *data, > /* no buffers in free list, attempt to allocate another rx buffer */ > /* unless the maximum count has been reached */ > if (n_hdlc->rx_buf_list.count < MAX_RX_BUF_COUNT) > - buf = kmalloc(N_HDLC_BUF_SIZE, GFP_ATOMIC); > + buf = kmalloc(struct_size(buf, buf, maxframe), > + GFP_ATOMIC); > } > > if (!buf) { > @@ -853,7 +852,7 @@ static struct n_hdlc *n_hdlc_alloc(void) > > /* allocate free rx buffer list */ > for(i=0;i - buf = kmalloc(N_HDLC_BUF_SIZE, GFP_KERNEL); > + buf = kmalloc(struct_size(buf, buf, maxframe), GFP_KERNEL); > if (buf) > n_hdlc_buf_put(&n_hdlc->rx_free_buf_list,buf); > else if (debuglevel >= DEBUG_LEVEL_INFO) > @@ -862,7 +861,7 @@ static struct n_hdlc *n_hdlc_alloc(void) > > /* allocate free tx buffer list */ > for(i=0;i - buf = kmalloc(N_HDLC_BUF_SIZE, GFP_KERNEL); > + buf = kmalloc(struct_size(buf, buf, maxframe), GFP_KERNEL); > if (buf) > n_hdlc_buf_put(&n_hdlc->tx_free_buf_list,buf); > else if (debuglevel >= DEBUG_LEVEL_INFO) > -- > 2.20.1 > There's no need for any of these variable length array patches to be backported anywhere. thanks, greg k-h