Re: [PATCH v3 09/17] iommufd: Add IOMMU_HWPT_INVALIDATE

[Jason Gunthorpe]

On Mon, Jul 31, 2023 at 10:07:32AM +0000, Liu, Yi L wrote:
> > > +		goto out_put_hwpt;
> > > +	}
> > > +
> > > +	/*
> > > +	 * Copy the needed fields before reusing the ucmd buffer, this
> > > +	 * avoids memory allocation in this path.
> > > +	 */
> > > +	user_ptr = cmd->data_uptr;
> > > +	user_data_len = cmd->data_len;
> > 
> > Uhh, who checks that klen < the temporary stack struct?
> 
> Take vtd as an example. The invalidate structure is struct iommu_hwpt_vtd_s1_invalidate[1].
> The klen is sizeof(struct iommu_hwpt_vtd_s1_invalidate)[2]. iommu_hwpt_vtd_s1_invalidate
> is also placed in the temporary stack struct (actually it is a union)[1]. So the klen should
> be <= temporary stack.

Ohh, I think I would add a few comments noting that the invalidate
structs need to be added to that union. Easy to miss.

> It's not so explicit though. Perhaps worth to have a check like below in this patch?
> 
> if (unlikely(klen > sizeof(union ucmd_buffer)))
> 	return -EINVAL;

Yes, stick this in the domain allocate path with a WARN_ON. The driver
is broken to allocate a domain with an invalid size.

Jason