If your Linux box is a Samba Server and you wish to enable access to it from other computers on your LAN.

Use these ufw commands to work the magic.

sudo ufw allow proto tcp from 10.11.12.0/24 to 10.11.12.19 port 445
sudo ufw allow proto udp from 10.11.12.0/24 to 10.11.12.19 port 137
sudo ufw allow proto udp from 10.11.12.0/24 to 10.11.12.19 port 138
sudo ufw allow proto tcp from 10.11.12.0/24 to 10.11.12.19 port 139

# Where 10.11.12.0/24 is your LAN's subnet address 
# and 10.11.12.19 is your Linux Samba box's IP Address.

# when you run ufw status you should get:
sudo ufw status
Status: active

To                         Action      From
--                         ------      ----
10.11.12.19 445/tcp      ALLOW       10.11.12.0/24
10.11.12.19 137/udp      ALLOW       10.11.12.0/24
10.11.12.19 138/udp      ALLOW       10.11.12.0/24
10.11.12.19 139/tcp      ALLOW       10.11.12.0/24

Port Information from here