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    SubjectRe: [v2.6.34-stable 134/165] mm: avoid null pointer access in vm_struct via /proc/vmallocinfo
    On Wed, Aug 15, 2012 at 03:47:58PM -0400, Paul Gortmaker wrote:
    > From: Mitsuo Hayasaka <mitsuo.hayasaka.hu@hitachi.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@hitachi.com>
    > Cc: Andrew Morton <akpm@linux-foundation.org>
    > Cc: David Rientjes <rientjes@google.com>
    > Cc: Namhyung Kim <namhyung@gmail.com>
    > Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
    > Cc: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
    > Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    > Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    > [PG: .34 has VMALLOC_START/END vs. start/end in f5252e009d5]
    > Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.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.

    --
    []'s
    Herton


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