From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail6.bemta8.messagelabs.com (mail6.bemta8.messagelabs.com [216.82.243.55]) by kanga.kvack.org (Postfix) with ESMTP id 9643D6B0169 for ; Sat, 20 Aug 2011 00:22:49 -0400 (EDT) Message-ID: <4E4F367B.8060904@hitachi.com> Date: Sat, 20 Aug 2011 13:22:19 +0900 From: HAYASAKA Mitsuo MIME-Version: 1.0 Subject: Re: [PATCH v2] avoid null pointer access in vm_struct References: <20110819105133.7504.62129.stgit@ltc219.sdl.hitachi.co.jp> <20110819155238.b11d19fb.akpm@linux-foundation.org> In-Reply-To: <20110819155238.b11d19fb.akpm@linux-foundation.org> Content-Type: text/plain; charset=ISO-2022-JP Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton , "Paul E. McKenney" Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, KOSAKI Motohiro , yrl.pp-manager.tt@hitachi.com, Namhyung Kim , David Rientjes , Jeremy Fitzhardinge Hi Paul and Andrew, (2011/08/20 3:53), Paul E. McKenney wrote: >> @@ -1562,6 +1561,7 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask, >> } >> area->pages[i] = page; >> } > Don't we need something here to prevent the compiler and/or the CPU > from reordering the assignment? Or am I missing how this is otherwise > prevented? > (2011/08/20 7:52), Andrew Morton wrote: > I think this is still just a workaround to fix up the real bug, and > that the real bug is that the vm_struct is installed into the vmlist > *before* it is fully initialised. It's just wrong to insert an object > into a globally-visible list and to then start populating it! If we > were instead to fully initialise the vm_struct and *then* insert it > into vmlist, the bug is fixed. > > Also I'd agree with Paul's concern regarding cross-CPU memory ordering. > I deeply agreed with both of your concern and comments. I'd like to create the patch where the vm_struct is installed into the vmlist *after* it is fully initialized. Thanks. (2011/08/20 7:52), Andrew Morton wrote: > On Fri, 19 Aug 2011 19:51:33 +0900 > Mitsuo Hayasaka wrote: > >> The /proc/vmallocinfo shows information about vmalloc allocations in vmlist >> that is a linklist of vm_struct. It, however, may access pages field of >> vm_struct where a page was not allocated, which results in a null pointer >> access and leads to a kernel panic. >> >> Why this happen: >> In __vmalloc_area_node(), the nr_pages field of vm_struct are set to the >> expected number of pages to be allocated, before the actual pages >> allocations. At the same time, when the /proc/vmallocinfo is read, it >> accesses the pages field of vm_struct according to the nr_pages field at >> show_numa_info(). Thus, a null pointer access happens. >> >> Patch: >> This patch sets nr_pages field of vm_struct AFTER the pages allocations >> finished in __vmalloc_area_node(). So, it can avoid accessing the pages >> field with unallocated page when show_numa_info() is called. > > I think this is still just a workaround to fix up the real bug, and > that the real bug is that the vm_struct is installed into the vmlist > *before* it is fully initialised. It's just wrong to insert an object > into a globally-visible list and to then start populating it! If we > were instead to fully initialise the vm_struct and *then* insert it > into vmlist, the bug is fixed. > > Also I'd agree with Paul's concern regarding cross-CPU memory ordering. > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org