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=-11.7 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 B53BAC43387 for ; Wed, 9 Jan 2019 12:13:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8357D2075C for ; Wed, 9 Jan 2019 12:13:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1547036030; bh=nIGWwD0klcXnbcLAvxM6/dCplJl11L1HQKEl3jZsPp8=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=e9rxuip5T31SUxU2JE254Xj6LdsCP1HJZPcjWL+8GEcndWKENDh/ikbe3tUdTNgF6 N8nGhtZmPcLO48aHEu91DcSzEGs/hM95jBNNajcWchYYhbzFXhO+NsswFLtFyT8F0g kSJDP1N1zNXiy1ZJVcIeEnO61pVaWqvX+7CT6oNA= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730544AbfAIMNu (ORCPT ); Wed, 9 Jan 2019 07:13:50 -0500 Received: from casper.infradead.org ([85.118.1.10]:58738 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730481AbfAIMNt (ORCPT ); Wed, 9 Jan 2019 07:13:49 -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=Cv4R96iykOaNa1kUSjLrXfKxwhDS33yToWCf/sw0PZA=; b=LEuZzfLvLWbCBZXJyEEoos+gSL JEqyl+rHLwn58F+rJ74jC6gcWE9ByPPaNc4IZ3qQ93Ep6RRutRwJM7v7I7NQu17NpTH8vno5AGjiK zM3ZweMhaRcfNAD6ct8sAb6JRA+7pTsK+CYDvmEcAHipLg0gmkWnkVw83YvT6C6W06ZW78lUmG51K 2G7wxHd3JnBWojhVlyUWrFYqy0ch38XLCVeeZFALnuhFUgr6c9EYpnx/6vq68iXD1lft+H8dRGdpB tUZKczaF0kaipvmRFhCNqncBRsge7AC8NaGJ54s3UxVJ6xyYN/QVhxXckkEWtacEbUShZz2y5imPl vx1+AScQ==; 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 1ghCjy-0000Js-TV; Wed, 09 Jan 2019 12:13:47 +0000 Date: Wed, 9 Jan 2019 10:13:42 -0200 From: Mauro Carvalho Chehab To: Laurent Pinchart Cc: Sakari Ailus , linux-media@vger.kernel.org, hverkuil@xs4all.nl Subject: Re: [PATCH v2 1/3] videobuf2-core: Prevent size alignment wrapping buffer size to 0 Message-ID: <20190109101342.54aa1373@coco.lan> In-Reply-To: <6971566.pIWyMH2Lze@avalon> References: <20190108085836.9376-1-sakari.ailus@linux.intel.com> <20190108134046.pxymxscc6cmlwyrq@paasikivi.fi.intel.com> <20190108123022.5dbead5b@coco.lan> <6971566.pIWyMH2Lze@avalon> 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, 08 Jan 2019 18:05:57 +0200 Laurent Pinchart escreveu: > On Tuesday, 8 January 2019 16:30:22 EET Mauro Carvalho Chehab wrote: > > Em Tue, 8 Jan 2019 15:40:47 +0200 > > > > Sakari Ailus escreveu: > > > On Tue, Jan 08, 2019 at 10:59:55AM -0200, Mauro Carvalho Chehab wrote: > > > > 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. > > > > > > How about: > > > > > > PAGE_ALIGN() may wrap the buffer length around to 0 if the value to be > > > aligned is close to the top of the value range of the type. Prevent this > > > by > > > checking that the aligned value is not smaller than the unaligned one. > > > > I would be a way more clear, as this is there to prevent a single > > special case: length == ULEN_MAX. Something like: > > > > If one tried to allocate a buffer with sizeof(ULEN_MAX), this will cause > > an overflow at PAGE_ALIGN(), making it return zero as the size of the > > buffer, causing the code to fail. > > > > I would even let it clearer at the code itself. So, instead of the > > hunk you proposed, I would do: > > > > unsigned long size = vb->planes[plane].length; > > > > /* Prevent PAGE_ALIGN overflow */ > > if (WARN_ON(size == ULONG_MAX)) > > goto free; > > ULONG_MAX - PAGE_SIZE + 2 to ULONG_MAX would all cause the same issue. True. The actual check should be: if (WARN_ON(size > ULONG_MAX - PAGE_SIZE + 1)) Not that the original proposal of checking after the overflow is wrong, but, IMHO, something linking the size to ULONG_MAX makes clearer about what kind of issue the code is meant to solve. A good comment before that would work fine. Thanks, Mauro