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pam_group — PAM module for group access
The pam_group PAM module does not authenticate the user, but instead it grants
group memberships (in the credential setting phase of the authentication
module) to the user. Such memberships are based on the service they are
By default rules for group memberships are taken from config file /etc/security
This module's usefulness relies on the file-systems accessible to the user. The
point being that once granted the membership of a group, the user may attempt
to create a setgid binary with a restricted group ownership. Later, when the
user is not given membership to this group, they can recover group membership
with the precompiled binary. The reason that the file-systems that the user has
access to are so significant, is the fact that when a system is mounted nosuid
the user is unable to create or execute such a binary file. For this module to
provide any level of security, all file-systems that the user has write access
to should be mounted nosuid.
The pam_group module functions in parallel with the /etc/group file. If the
user is granted any groups based on the behavior of this module, they are
granted in addition to those entries /etc/group (or equivalent).
These are some example lines which might be specified in /etc/security/
Running 'xsh' on tty* (any ttyXXX device), the user 'us' is given access to the
floppy (through membership of the floppy group)
Running 'xsh' on tty* (any ttyXXX device), the user 'sword' is given access to
games (through membership of the floppy group) after work hours.
xsh; tty* ;sword;!Wk0900-1800;games, sound
xsh; tty* ;*;Al0900-1800;floppy
Any member of the group 'admin' running 'xsh' on tty*, is granted access (at
any time) to the group 'plugdev'
xsh; tty* ;%admin;Al0000-2400;plugdev