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

[Herton Ronaldo Krzesinski]

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.

-- 
[]'s
Herton
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