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=-11.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,URIBL_BLOCKED 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 0EC3EC43387 for ; Tue, 8 Jan 2019 13:00:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CD33A2087E for ; Tue, 8 Jan 2019 13:00:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1546952401; bh=9v6z0PHx16Srrjjk9bhQq1K2HPnrTbUvfJEX7Vw/Xdg=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=YyGwQFDXYgUyuoQdCpNZuLMPAVEFklFqLAyPlK0WF+T2ETfuBFlkDAQmXAUk39akV 4hDihE3gS7M1ome6PxCcz9U464xDqQvV+GIhsbqmvt6TpRKduGrKd+Ayotg9300N/t 74m+mnShwMRNqPsgi8npP5eofL4tPo44qXlD40+A= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727941AbfAHNAB (ORCPT ); Tue, 8 Jan 2019 08:00:01 -0500 Received: from casper.infradead.org ([85.118.1.10]:49660 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727558AbfAHNAB (ORCPT ); Tue, 8 Jan 2019 08:00:01 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=Content-Transfer-Encoding:Content-Type: MIME-Version:References:In-Reply-To:Message-ID:Subject:Cc:To:From:Date:Sender :Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help: List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=2YxERaHGs9ffLqONjGUrRxyS1EZF8etWUA5pEYx2lN4=; b=oYk12YmW5VgWxP7/5XCJB/V973 zSEqZnPFduOuBHyU/3yZnas9LCLOY3uEVY1pBCMitZ9B2X8Eurnt10+XY+30cFOrDEwjXCBjvmvbT BUHQJ8Rh9NVkfvm4I/QHNH391E1BjZO0dJe2hAUQSSd0xXzPrpH4jlXDLQpLmxxkCoKfhgOWJn+66 u1Yme4OGvnEDPTRBE1D4NRqhE4GEDntb9UXyxCxKQWAhSeRxxSYOWy8Nphua4WfEW4OCQLbCdaAnv z8924/VfXhUyBXp91Z9QYg7MCnwQLhmJToVPQHLl0iNY21yVqM8j93ps8fYLeE31+dX6hhz2QgQJm oGRcLguQ==; Received: from 177.41.113.230.dynamic.adsl.gvt.net.br ([177.41.113.230] helo=coco.lan) by casper.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1ggqz9-0002pM-JG; Tue, 08 Jan 2019 12:59:59 +0000 Date: Tue, 8 Jan 2019 10:59:55 -0200 From: Mauro Carvalho Chehab To: Sakari Ailus Cc: linux-media@vger.kernel.org, hverkuil@xs4all.nl, laurent.pinchart@ideasonboard.com Subject: Re: [PATCH v2 1/3] videobuf2-core: Prevent size alignment wrapping buffer size to 0 Message-ID: <20190108105955.68009949@coco.lan> In-Reply-To: <20190108105212.66837b9a@coco.lan> References: <20190108085836.9376-1-sakari.ailus@linux.intel.com> <20190108085836.9376-2-sakari.ailus@linux.intel.com> <20190108105212.66837b9a@coco.lan> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-media-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org Em Tue, 8 Jan 2019 10:52:12 -0200 Mauro Carvalho Chehab escreveu: > Em Tue, 8 Jan 2019 10:58:34 +0200 > Sakari Ailus escreveu: > > > PAGE_ALIGN() may wrap the buffer size around to 0. Prevent this by > > checking that the aligned value is not smaller than the unaligned one. > > > > Note on backporting to stable: the file used to be under > > drivers/media/v4l2-core, it was moved to the current location after 4.14. > > > > Signed-off-by: Sakari Ailus > > Cc: stable@vger.kernel.org > > Reviewed-by: Hans Verkuil > > --- > > drivers/media/common/videobuf2/videobuf2-core.c | 4 ++++ > > 1 file changed, 4 insertions(+) > > > > diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c > > index 0ca81d495bda..0234ddbfa4de 100644 > > --- a/drivers/media/common/videobuf2/videobuf2-core.c > > +++ b/drivers/media/common/videobuf2/videobuf2-core.c > > @@ -207,6 +207,10 @@ static int __vb2_buf_mem_alloc(struct vb2_buffer *vb) > > for (plane = 0; plane < vb->num_planes; ++plane) { > > unsigned long size = PAGE_ALIGN(vb->planes[plane].length); > > > > + /* Did it wrap around? */ > > + if (size < vb->planes[plane].length) > > + goto free; > > + > > Sorry, but I can't see how this could ever happen (except for a very serious > bug at the compiler or at the hardware). > > See, the definition at PAGE_ALIGN is (from mm.h): > > #define PAGE_ALIGN(addr) ALIGN(addr, PAGE_SIZE) > > and the macro it uses come from kernel.h: > > #define __ALIGN_KERNEL(x, a) __ALIGN_KERNEL_MASK(x, (typeof(x))(a) - 1) > #define __ALIGN_KERNEL_MASK(x, mask) (((x) + (mask)) & ~(mask)) > .. > #define ALIGN(x, a) __ALIGN_KERNEL((x), (a)) > > So, this: > size = PAGE_ALIGN(length); > > (assuming PAGE_SIZE= 0x1000) > > becomes: > > size = (length + 0x0fff) & ~0xfff; > > so, size will *always* be >= length. Hmm... after looking at patch 2, now I understand what's your concern... If someone indeed uses length = INT_MAX, size will indeed be zero. Please adjust the description accordingly, as it doesn't reflect that. Btw, in this particular case, I would use a WARN_ON(), as this is something that indicates not only a driver bug (as the driver is letting someone to request a buffer a way too big), but probably also an attempt from a hacker to try to crack the system. Thanks, Mauro