From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <SRS0=Fmhj=NM=vger.kernel.org=linux-kernel-owner@kernel.org>
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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,
	MAILING_LIST_MULTI,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 E6937C6786F
	for <linux-kernel@archiver.kernel.org>; Thu,  1 Nov 2018 21:47:32 +0000 (UTC)
Received: from vger.kernel.org (vger.kernel.org [209.132.180.67])
	by mail.kernel.org (Postfix) with ESMTP id B426220820
	for <linux-kernel@archiver.kernel.org>; Thu,  1 Nov 2018 21:47:32 +0000 (UTC)
DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B426220820
Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org
Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1727602AbeKBGwQ (ORCPT
        <rfc822;linux-kernel@archiver.kernel.org>);
        Fri, 2 Nov 2018 02:52:16 -0400
Received: from mail.linuxfoundation.org ([140.211.169.12]:33824 "EHLO
        mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1726167AbeKBGwQ (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Fri, 2 Nov 2018 02:52:16 -0400
Received: from akpm3.svl.corp.google.com (unknown [104.133.8.65])
        by mail.linuxfoundation.org (Postfix) with ESMTPSA id 815D4AA6;
        Thu,  1 Nov 2018 21:47:29 +0000 (UTC)
Date:   Thu, 1 Nov 2018 14:47:23 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     <miles.chen@mediatek.com>
Cc:     Michal Hocko <mhocko@suse.com>, Joe Perches <joe@perches.com>,
        Matthew Wilcox <willy@infradead.org>, <linux-mm@kvack.org>,
        <linux-kernel@vger.kernel.org>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-mediatek@lists.infradead.org>, <wsd_upstream@mediatek.com>,
        Michal Hocko <mhocko@kernel.org>
Subject: Re: [PATCH v4] mm/page_owner: clamp read count to PAGE_SIZE
Message-Id: <20181101144723.3ddc1fa1ab7f81184bc2fdb8@linux-foundation.org>
In-Reply-To: <1541091607-27402-1-git-send-email-miles.chen@mediatek.com>
References: <1541091607-27402-1-git-send-email-miles.chen@mediatek.com>
X-Mailer: Sylpheed 3.6.0 (GTK+ 2.24.31; x86_64-pc-linux-gnu)
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Fri, 2 Nov 2018 01:00:07 +0800 <miles.chen@mediatek.com> wrote:

> From: Miles Chen <miles.chen@mediatek.com>
> 
> The page owner read might allocate a large size of memory with
> a large read count. Allocation fails can easily occur when doing
> high order allocations.
> 
> Clamp buffer size to PAGE_SIZE to avoid arbitrary size allocation
> and avoid allocation fails due to high order allocation.
> 
> ...
>
> --- a/mm/page_owner.c
> +++ b/mm/page_owner.c
> @@ -351,6 +351,7 @@ print_page_owner(char __user *buf, size_t count, unsigned long pfn,
>  		.skip = 0
>  	};
>  
> +	count = count > PAGE_SIZE ? PAGE_SIZE : count;
>  	kbuf = kmalloc(count, GFP_KERNEL);
>  	if (!kbuf)
>  		return -ENOMEM;

A bit tidier:

--- a/mm/page_owner.c~mm-page_owner-clamp-read-count-to-page_size-fix
+++ a/mm/page_owner.c
@@ -351,7 +351,7 @@ print_page_owner(char __user *buf, size_
 		.skip = 0
 	};
 
-	count = count > PAGE_SIZE ? PAGE_SIZE : count;
+	count = min_t(size_t, count, PAGE_SIZE);
 	kbuf = kmalloc(count, GFP_KERNEL);
 	if (!kbuf)
 		return -ENOMEM;