On Thu, May 30, 2024 at 04:15:51PM +0200, Thorsten Blum wrote:
> Hi Dan,
>
> On 27. May 2024, at 12:38, Dan Carpenter <dan.carpenter@xxxxxxxxxx> wrote:
> > Also this check isn't great:
> >
> > if (dev->policy_sz < header->length + 512)
> >
> > header->length is a u32 that comes from the user, so the addition can
> > overflow. I can't immediately see how to exploit this though since we
> > don't seem to use header->length after this (by itself).
>
> How about
>
> if (header->length > U32_MAX - 512 || dev->policy_sz < header->length + 512)
> return -EINVAL;
>
> to prevent a possible overflow?
I've been thinking about this and actually we could do something simpler:
if (dev->policy_sz < size_add(header->length, 512)) {
>
> header->length is used in the next line
>
> dev->policy_sz = header->length + 512;
Yeah, but it's not used by itself. The "header->length + 512" has been
verified as a valid value whether it overflows or not. Only
"header->length" is wrong.
>
> and if the addition overflows, we end up setting dev->policy_sz to an
> invalid value.
regards,
dan carpenter
