Re: [PATCH] vfio: Fix ksize arg while copying user struct in vfio_df_ioctl_bind_iommufd()

[Jason Gunthorpe]

On Thu, Oct 30, 2025 at 05:12:38PM +0000, Raghavendra Rao Ananta wrote:
> For the cases where user includes a non-zero value in 'token_uuid_ptr'
> field of 'struct vfio_device_bind_iommufd', the copy_struct_from_user()
> in vfio_df_ioctl_bind_iommufd() fails with -E2BIG. For the 'minsz' passed,
> copy_struct_from_user() expects the newly introduced field to be zero-ed,
> which would be incorrect in this case.
> 
> Fix this by passing the actual size of the kernel struct. If working
> with a newer userspace, copy_struct_from_user() would copy the
> 'token_uuid_ptr' field, and if working with an old userspace, it would
> zero out this field, thus still retaining backward compatibility.
> 
> Fixes: 86624ba3b522 ("vfio/pci: Do vf_token checks for VFIO_DEVICE_BIND_IOMMUFD")
> Signed-off-by: Raghavendra Rao Ananta <rananta@xxxxxxxxxx>
> ---
>  drivers/vfio/device_cdev.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Cc: stable@xxxxxxxxxxxxxxx
Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>

Though I feel this was copied from some other spot in vfio so I wonder
if we have a larger set of things that are a little off..

Jason