pam_group.so
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 applying for.
By default rules for group memberships are taken from config file
/etc/security/group.conf.
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).
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 applying for.
For this module to function correctly there must be a correctly
formatted /etc/security/group.conf file present.
White spaces are ignored and lines maybe extended with '\' (escaped
newlines). Text following a '#' is ignored to the end of the line.
The syntax of the lines is as follows:
services;ttys;users;times;groups
The first field, the services field, is a logic list
of PAM service names that the rule applies to.
The second field, the tty
field, is a logic list of terminal names that this rule applies to.
The third field, the users
field, is a logic list of users, or a UNIX group, or a netgroup of
users to whom this rule applies. Group names are preceded by a '%'
symbol, while netgroup names are preceded by a '@' symbol.
A logic list namely means individual tokens that are optionally prefixed with '!' (logical not) and separated with '&' (logical and) and '|' (logical or).
For these items the simple wildcard '*' may be used only once. With UNIX groups or netgroups no wildcards or logic operators are allowed.
The times field is used to indicate "when"
these groups are to be given to the user. The format here is a logic
list of day/time-range entries. The days are specified by a sequence of
two character entries, MoTuSa for example is Monday Tuesday and Saturday.
Note that repeated days are unset MoMo = no day, and MoWk = all weekdays
bar Monday. The two character combinations accepted are Mo Tu We Th Fr Sa
Su Wk Wd Al, the last two being week-end days and all 7 days of the week
respectively. As a final example, AlFr means all days except Friday.
Each day/time-range can be prefixed with a '!' to indicate "anything but". The time-range part is two 24-hour times HHMM, separated by a hyphen, indicating the start and finish time (if the finish time is smaller than the start time it is deemed to apply on the following day).
The groups field is a comma or space
separated list of groups that the user inherits membership of. These
groups are added if the previous fields are satisfied by the user's request.
For a rule to be active, ALL of service+ttys+users must be satisfied by the applying process.
group membership was granted.
Not all relevant data could be gotten.
Memory buffer error.
Group membership was not granted.
pam_sm_authenticate was called which does nothing.
The user is not known to the system.
These are some example lines which might be specified in
/etc/security/group.conf.
Running 'xsh' on tty* (any ttyXXX device), the user 'us' is given access to the floppy (through membership of the floppy group)
xsh;tty*&!ttyp*;us;Al0000-2400;floppy
Running 'xsh' on tty* (any ttyXXX device), the users 'sword', 'pike' and 'shield' are given access to games (through membership of the floppy group) after work hours.
xsh; tty* ;sword|pike|shield;!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