Re: [PATCH v2] platform/x86/amd/pmf: Use memdup_user()

[Dan Carpenter <dan.carpenter@linaro.org>]

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@linaro.org> 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