Re: [Qemu-devel] [PATCH for-4.0-maybe] device_tree: Fix integer overflowing in load_device_tree()

[David Gibson <david@gibson.dropbear.id.au>]

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On Tue, Apr 09, 2019 at 08:59:55PM +0200, Philippe Mathieu-Daudé wrote:
> On 4/9/19 7:40 PM, Markus Armbruster wrote:
> > If the value of get_image_size() exceeds INT_MAX / 2 - 10000, the
> > computation of @dt_size overflows to a negative number, which then
> > gets converted to a very large size_t for g_malloc0() and
> > load_image_size().  In the (fortunately improbable) case g_malloc0()
> > succeeds and load_image_size() survives, we'd assign the negative
> > number to *sizep.  What that would do to the callers I can't say, but
> > it's unlikely to be good.
> > 
> > Fix by rejecting images whose size would overflow.
> > 
> > Signed-off-by: Markus Armbruster <armbru@redhat.com>
> > ---
> >  device_tree.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> > 
> > diff --git a/device_tree.c b/device_tree.c
> > index 296278e12a..f8b46b3c73 100644
> > --- a/device_tree.c
> > +++ b/device_tree.c
> > @@ -84,6 +84,10 @@ void *load_device_tree(const char *filename_path, int *sizep)
> >                       filename_path);
> >          goto fail;
> >      }
> > +    if (dt_size > INT_MAX / 2 - 10000) {
> 
> We should avoid magic number duplication.
> That said, this patch looks safe.
> 
> Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>

As Philippe says, the test condition is kinda ugly and I hope we can
refine it in future.  But since it fixes a real problem for now,

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
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http://www.ozlabs.org/~dgibson

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