Re: [PATCH v3 08/17] iommufd: IOMMU_HWPT_ALLOC allocation with user data

[Jason Gunthorpe]

On Wed, Aug 02, 2023 at 04:42:10PM -0700, Nicolin Chen wrote:
> On Mon, Jul 31, 2023 at 10:16:17AM -0300, Jason Gunthorpe wrote:
>  
> > > Ideally expanding uAPI structure size should come with new flag bits.
> > 
> > Flags or some kind of 'zero is the same behavior as a smaller struct'
> > scheme.
> > 
> > This patch is doing the zero option:
> > 
> >  	__u32 __reserved;
> > +	__u32 hwpt_type;
> > +	__u32 data_len;
> > +	__aligned_u64 data_uptr;
> >  };
> > 
> > hwpt_type == 0 means default type
> > data_len == 0 means no data
> > data_uptr is ignored (zero is safe)
> > 
> > So there is no need to change it
> 
> TEST_LENGTH passing ".size = sizeof(struct _struct) - 1" expects a
> -EINVAL error code from "if (ucmd.user_size < op->min_size)" check
> in the iommufd_fops_ioctl(). This has been working when min_size is
> exactly the size of the structure.
> 
> When the size of the structure becomes larger than min_size, i.e.
> the passing size above is larger than min_size, it bypasses that
> min_size sanity and goes down to an ioctl handler with a potential
> risk. And actually, the size range can be [min_size, struct_size),
> making it harder for us to sanitize with the existing code.
> 
> I wonder what's the generic way of sanitizing this case? And, it
> seems that TEST_LENGTH needs some rework to test min_size only?

Yes, it should technically test using offsetof and a matching set of
struct members.

Jason