zfs_ioc_recv, zfs_ioc_send* do not seem to check fd opening mode
It seems that
zfs_ioc_send and possibly other ioctl handlers do not check the fd opening mode.
For example, if a descriptor opened with
O_RDONLY is passed to
zfs_ioc_send, then the latter will happily write to it unless the object can not be written for other reason.
It would be nice if the mode was checked.