Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755272AbcLNJMR (ORCPT ); Wed, 14 Dec 2016 04:12:17 -0500 Received: from mail-qk0-f169.google.com ([209.85.220.169]:34327 "EHLO mail-qk0-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755018AbcLNJMP (ORCPT ); Wed, 14 Dec 2016 04:12:15 -0500 From: Ard Biesheuvel To: linux-arm-kernel@lists.infradead.org, will.deacon@arm.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org Cc: catalin.marinas@arm.com, akpm@linux-foundation.org, hanjun.guo@linaro.org, xieyisheng1@huawei.com, rrichter@cavium.com, james.morse@arm.com, Ard Biesheuvel Subject: [PATCH 1/2] mm: don't dereference struct page fields of invalid pages Date: Wed, 14 Dec 2016 09:11:46 +0000 Message-Id: <1481706707-6211-2-git-send-email-ard.biesheuvel@linaro.org> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1481706707-6211-1-git-send-email-ard.biesheuvel@linaro.org> References: <1481706707-6211-1-git-send-email-ard.biesheuvel@linaro.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1167 Lines: 37 The VM_BUG_ON() check in move_freepages() checks whether the node id of a page matches the node id of its zone. However, it does this before having checked whether the struct page pointer refers to a valid struct page to begin with. This is guaranteed in most cases, but may not be the case if CONFIG_HOLES_IN_ZONE=y. So reorder the VM_BUG_ON() with the pfn_valid_within() check. Signed-off-by: Ard Biesheuvel --- mm/page_alloc.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index f64e7bcb43b7..4e298e31fa86 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1864,14 +1864,14 @@ int move_freepages(struct zone *zone, #endif for (page = start_page; page <= end_page;) { - /* Make sure we are not inadvertently changing nodes */ - VM_BUG_ON_PAGE(page_to_nid(page) != zone_to_nid(zone), page); - if (!pfn_valid_within(page_to_pfn(page))) { page++; continue; } + /* Make sure we are not inadvertently changing nodes */ + VM_BUG_ON_PAGE(page_to_nid(page) != zone_to_nid(zone), page); + if (!PageBuddy(page)) { page++; continue; -- 2.7.4