Re: [v2.6.34-stable 134/165] mm: avoid null pointer access in vm_structvia /proc/vmallocinfo

[Paul Gortmaker]

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@xxxxxxxxxxx>
>>
>>                    -------------------
>>     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@xxxxxxxxxxx>
>> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
>> Cc: David Rientjes <rientjes@xxxxxxxxxx>
>> Cc: Namhyung Kim <namhyung@xxxxxxxxx>
>> Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
>> Cc: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>
>> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
>> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
>> [PG: .34 has VMALLOC_START/END vs. start/end in f5252e009d5]
>> Signed-off-by: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
> [...]
> 
> 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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