According to this writeup ufs kernel module is compiled with only read permissions. I could mount a ufs partition with this command:
sudo mount -t ufs -r -o ufstype=ufs2 /dev/mapper/loop0p1 /mnt/freebsd/
And it mounts the filesystem without write permissions. There is a ufs-utils package for Debian/Ubuntu but I could not figure out how to use it. So there any way to get read/write permissions work for ufs on Ubuntu/Linux.