linux-kernel - Re: [v2.6.34-stable 134/165] mm: avoid null pointer access in vm

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Message-ID: <502E8CC7.4070401@windriver.com>
Date:	Fri, 17 Aug 2012 14:26:15 -0400
From:	Paul Gortmaker <paul.gortmaker@...driver.com>
To:	Herton Ronaldo Krzesinski <herton.krzesinski@...onical.com>
CC:	<stable@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	Mitsuo Hayasaka <mitsuo.hayasaka.hu@...achi.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>,
	Namhyung Kim <namhyung@...il.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>,
	Luciano Chavez <lnx1138@...ux.vnet.ibm.com>,
	Rik van Riel <riel@...hat.com>, Willy Tarreau <w@....eu>
Subject: Re: [v2.6.34-stable 134/165] mm: avoid null pointer access in vm_struct
 via /proc/vmallocinfo

On 12-08-17 11:22 AM, Herton Ronaldo Krzesinski wrote:
> On Wed, Aug 15, 2012 at 03:47:58PM -0400, Paul Gortmaker wrote:
>> From: Mitsuo Hayasaka <mitsuo.hayasaka.hu@...achi.com>
>>
>>                    -------------------
>>     This is a commit scheduled for the next v2.6.34 longterm release.
>>     http://git.kernel.org/?p=linux/kernel/git/paulg/longterm-queue-2.6.34.git
>>     If you see a problem with using this for longterm, please comment.
>>                    -------------------
>>
>> commit f5252e009d5b87071a919221e4f6624184005368 upstream.
>>
>> 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.  This results in a null
>> pointer access and leads to a kernel panic.
>>
>> Why this happens: In __vmalloc_node_range() called from vmalloc(), newly
>> allocated vm_struct is added to vmlist at __get_vm_area_node() and then,
>> some fields of vm_struct such as nr_pages and pages are set at
>> __vmalloc_area_node().  In other words, it is added to vmlist before it is
>> fully initialized.  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.
>>
>> The patch adds the newly allocated vm_struct to the vmlist *after* it is
>> fully initialized.  So, it can avoid accessing the pages field with
>> unallocated page when show_numa_info() is called.
>>
>> Signed-off-by: Mitsuo Hayasaka <mitsuo.hayasaka.hu@...achi.com>
>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>> Cc: David Rientjes <rientjes@...gle.com>
>> Cc: Namhyung Kim <namhyung@...il.com>
>> Cc: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
>> Cc: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
>> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
>> Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
>> [PG: .34 has VMALLOC_START/END vs. start/end in f5252e009d5]
>> Signed-off-by: Paul Gortmaker <paul.gortmaker@...driver.com>
> [...]
> 
> commit 1368edf0647ac112d8cfa6ce47257dc950c50f5c ("mm: vmalloc: check for
> page allocation failure before vmlist insertion") addresses a regression
> on this change, something to consider for inclusion in this stable
> update as well.

Thanks Herton.

I've added Willy to CC, since v2.6.32.49 added f5252e but does
not have 1368edf0 yet in any 2.6.32.x

Paul.
--

> 
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