vfio: Fix ksize arg while copying user struct in vfio_df_ioctl_bind_iommufd()

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")
Cc: [e-mail]
Signed-off-by: Raghavendra Rao Ananta <[e-mail]>
Reviewed-by: Jason Gunthorpe <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alex Williamson <[e-mail]>

drivers/vfio/device_cdev.c

···
 		return ret;
 	if (user_size < minsz)
 		return -EINVAL;
-	ret = copy_struct_from_user(&bind, minsz, arg, user_size);
+	ret = copy_struct_from_user(&bind, sizeof(bind), arg, user_size);
 	if (ret)
 		return ret;