Re: [PATCH] kernel buffer overflow kmalloc_slab() fix

[J Freyensee <james_p_freyensee@linux.intel.com>]

On Thu, 2011-05-19 at 16:24 -0500, Christoph Lameter wrote:
> On Thu, 19 May 2011, J Freyensee wrote:
> 
> > On Thu, 2011-05-19 at 15:51 -0500, Christoph Lameter wrote:
> > > On Thu, 19 May 2011, james_p_freyensee@linux.intel.com wrote:
> > >
> > > > From: J Freyensee <james_p_freyensee@linux.intel.com>
> > > >
> > > > Currently, kmalloc_index() can return -1, which can be
> > > > passed right to the kmalloc_caches[] array, cause a
> > >
> > > No kmalloc_index() cannot return -1 for the use case that you are
> > > considering here. The value passed as a size to
> > > kmalloc_slab is bounded by 2 * PAGE_SIZE and kmalloc_slab will only return
> > > -1 for sizes > 4M. So we will have to get machines with page sizes > 2M
> > > before this can be triggered.
> > >
> > >
> >
> > Okay.  I thought it would still be good to check for -1 anyways, even if
> > machines today cannot go above 2M page sizes.  I would think it would be
> > better for software code to always make sure a case that this could
> > never happen instead of relying on whatever physical hardware limits the
> > linux kernel could be running on on today's machines or future machines,
> > because technology has shown limits can change.  I would think
> > regardless what this code runs on, this is still a software flaw that
> > can be considered not a good thing to allow lying around in software
> > code that can easily be fixed.
> 
> This is basically macro style code that is mostly folded at compile time
> and we have to obey certain restrictions to convince the compiler to
> properly do that. Took us a long time to get that right.
> 
> Not sure what to do instead of returning -1 in kmalloc_slab. 

I think returning -1 is fine; I just think code using the function
should be checking for it and protect itself for errors in kernel space.


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