Re: [PATCH] virt: acrn: Prefer array_syze and struct_size over open coded arithmetic

Kees Cook
2021-10-13T07:29:17Z

On Tue, Oct 12, 2021 at 09:34:29AM +0800, Li Fei1 wrote:
> On Mon, Oct 11, 2021 at 12:39:02PM +0200, Len Baker wrote:
> > As noted in the "Deprecated Interfaces, Language Features, Attributes,
> > and Conventions" documentation [1], size calculations (especially
> > multiplication) should not be performed in memory allocator (or similar)
> > function arguments due to the risk of them overflowing. This could lead
> > to values wrapping around and a smaller allocation being made than the
> > caller was expecting. Using those allocations could lead to linear
> > overflows of heap memory and other misbehaviors.
> >
> > So, use the array_size() helper to do the arithmetic instead of the
> > argument "count * size" in the vzalloc() function.
> >
> > Also, take the opportunity to add a flexible array member of struct
> > vm_memory_region_op to the vm_memory_region_batch structure. And then,
> > change the code accordingly and use the struct_size() helper to do the
> > arithmetic instead of the argument "size + size * count" in the kzalloc
> > function.
> >
> > This code was detected with the help of Coccinelle and audited and fixed
> > manually.
> >
> > [1] https://www.kernel.org/doc/html/latest/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments
> >
> > Signed-off-by: Len Baker <len.baker@gmx.com>
>
> Hi Baker
>
> Thanks for helping us to fix this issue. This patch looks good to me.
> Please add Signed-off-by: Fei Li <fei1.li@intel.com>.
> Only two minor comments.

For v2, please fix the Subject typo, too. :) "syze" -> "size".

-Kees

--
Kees Cook