maddy/cmd/maddy-shadow-helper

maddy-shadow-helper

External helper binary for interaction with shadow passwords database. Unlike maddy-pam-helper it supports only local shadow database but it does not have any C dependencies.

Installation

maddy-shadow-helper is kinda dangerous binary and should not be allowed to be executed by everybody but maddy's user. At the same moment it needs to have access to read-protected files. For this reason installation should be done very carefully to make sure to not introduce any security "holes".

First method

chown maddy: /usr/bin/maddy-shadow-helper
chmod u+x,g-x,o-x /usr/bin/maddy-shadow-helper

Also maddy-shadow-helper needs access to /etc/shadow, one of the ways to provide it is to set file capability CAP_DAC_READ_SEARCH:

setcap cap_dac_read_search+ep /usr/bin/maddy-shadow-helper

Second method

Another, less restrictive is to make it setuid-root (assuming you have both maddy user and group):

chown root:maddy /usr/bin/maddy-shadow-helper
chmod u+xs,g+x,o-x /usr/bin/maddy-shadow-helper

Third method

The best way actually is to create shadow group and grant access to /etc/shadow to it and then make maddy-shadow-helper setgid-shadow:

groupadd shadow
chown :shadow /etc/shadow
chmod g+r /etc/shadow
chown maddy:shadow /usr/bin/maddy-shadow-helper
chmod u+x,g+xs /usr/bin/maddy-shadow-helper

Pick what works best for you.