Messages in this thread | | | Date | Tue, 6 Jan 2009 14:57:41 +0900 | From | KAMEZAWA Hiroyuki <> | Subject | Re: [PATCH] mm: __nr_to_section - make it safe against overflow v2 |
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On Mon, 5 Jan 2009 16:37:42 -0800 Andrew Morton <akpm@linux-foundation.org> wrote:
> On Mon, 5 Jan 2009 13:31:32 +0300 > Cyrill Gorcunov <gorcunov@gmail.com> wrote: > > > __nr_to_section should check for array bound overflow. > > We should better get NULL dereference then silently > > pass some memory snippet out of bounds to a caller. > > > > Are there actually any known problems here? >
IIRC, I never saw any problem. (But I may see in memory-hotplug development.) I don't like adding any check here.
This __nr_to_section[] is very internal function and will not be accessed directly by codes other than VM(of sparsemem and memory hotplug).
For general users, this function will be called via pfn_to_page(). So, this means what this patch should really do is checking "pfn" argugments to pfn_to_page(). Of course, I don't want any check in pfn_to_page()'s "pfn" range.But, pfn_to_page() is usually called with pfn_valid() if necessary. pfn_valid() and pfn_present(), other callers of this, check this in explicit way.
Cyrill, if you really want to do check "idx", please add
== __nr_to_section_direct(unsigned long nr) (or some better name) { BUG_ON(nr >NR_SECTION_ROOTS); return __nr_to_section(nr); } == to, mm/internal.h or somewhere. and use this in sparse.c and memhotplug.c
So, Nack from me for now.
Thanks, -Kame
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