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    SubjectRe: + sys_getppid-oopses-on-debug-kernel.patch added to -mm tree
    On 2006.08.08 17:39:37 +0300, Muli Ben-Yehuda wrote:
    > On Tue, Aug 08, 2006 at 07:32:51AM -0700, akpm@osdl.org wrote:
    > >
    > > The patch titled
    > >
    > > sys_getppid() oopses on debug kernel
    > >
    > > has been added to the -mm tree. Its filename is
    > >
    > > sys_getppid-oopses-on-debug-kernel.patch
    > >
    > > See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
    > > out what to do about this
    > >
    > > ------------------------------------------------------
    > > Subject: sys_getppid() oopses on debug kernel
    > > From: Kirill Korotaev <dev@sw.ru>
    > >
    > > sys_getppid() optimization can access a freed memory. On kernels with
    > > DEBUG_SLAB turned ON, this results in Oops.
    > >
    > > Signed-off-by: Kirill Korotaev <dev@openvz.org>
    > > Cc: <stable@kernel.org>
    > > Signed-off-by: Andrew Morton <akpm@osdl.org>
    >
    > I'm probably missing something, but is it really valid to access freed
    > kernel memory even if CONFIG_DEBUG_SLAB is off - as this patch does?

    There's a note right above the function that explains it:
    * NOTE! This depends on the fact that even if we _do_
    * get an old value of "parent", we can happily dereference
    * the pointer (it was and remains a dereferencable kernel pointer
    * no matter what): we just can't necessarily trust the result
    * until we know that the parent pointer is valid.

    HTH
    Björn
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