6.1. pam_access - logdaemon style login access control
pam_access.so [ debug ] [ nodefgroup ] [ noaudit ] [ accessfile=file ] [ fieldsep=sep ] [ listsep=sep ]
The pam_access PAM module is mainly for access management. It provides logdaemon style login access control based on login names, host or domain names, internet addresses or network numbers, or on terminal line names, X $DISPLAY values, or PAM service names in case of non-networked logins.
By default rules for access management are taken from config file /etc/security/access.conf if you don't specify another file. Then individual *.conf files from the /etc/security/access.d/ directory are read. The files are parsed one after another in the order of the system locale. The effect of the individual files is the same as if all the files were concatenated together in the order of parsing. This means that once a pattern is matched in some file no further files are parsed. If a config file is explicitly specified with the accessfile option the files in the above directory are not parsed.
If Linux PAM is compiled with audit support the module will report when it denies access based on origin (host, tty, etc.).
The /etc/security/access.conf file specifies (user/group, host), (user/group, network/netmask), (user/group, tty), (user/group, X-$DISPLAY-value), or (user/group, pam-service-name) combinations for which a login will be either accepted or refused.
When someone logs in, the file access.conf is scanned for the first entry that matches the (user/group, host) or (user/group, network/netmask) combination, or, in case of non-networked logins, the first entry that matches the (user/group, tty) combination, or in the case of non-networked logins without a tty, the first entry that matches the (user/group, X-$DISPLAY-value) or (user/group, pam-service-name/) combination. The permissions field of that table entry determines whether the login will be accepted or refused.
Each line of the login access control table has three fields separated by a ":" character (colon):
permission:users/groups:origins
The first field, the permission field, can be either a "+" character (plus) for access granted or a "-" character (minus) for access denied.
The second field, the users/group field, should be a list of one or more login names, group names, or ALL (which always matches). To differentiate user entries from group entries, group entries should be written with brackets, e.g. (group).
The third field, the origins field, should be a list of one or more tty names (for non-networked logins), X $DISPLAY values or PAM service names (for non-networked logins without a tty), host names, domain names (begin with "."), host addresses, internet network numbers (end with "."), internet network addresses with network mask (where network mask can be a decimal number or an internet address also), ALL (which always matches) or LOCAL. The LOCAL keyword matches if and only if pam_get_item(3), when called with an item_type of PAM_RHOST, returns NULL or an empty string (and therefore the origins field is compared against the return value of pam_get_item(3) called with an item_type of PAM_TTY or, absent that, PAM_SERVICE).
If supported by the system you can use @netgroupname in host or user patterns. The @@netgroupname syntax is supported in the user pattern only and it makes the local system hostname to be passed to the netgroup match call in addition to the user name. This might not work correctly on some libc implementations causing the match to always fail.
The EXCEPT operator makes it possible to write very compact rules.
If the nodefgroup is not set, the group file is searched when a name does not match that of the logged-in user. Only groups are matched in which users are explicitly listed. However the PAM module does not look at the primary group id of a user.
The "#" character at start of line (no space at front) can be used to mark this line as a comment line.
-
accessfile=/path/to/access.conf -
Indicate an alternative
access.confstyle configuration file to override the default. This can be useful when different services need different access lists. -
debug -
A lot of debug information is printed with syslog(3).
-
noaudit -
Do not report logins from disallowed hosts and ttys to the audit subsystem.
-
fieldsep=separators -
This option modifies the field separator character that pam_access will recognize when parsing the access configuration file. For example: fieldsep=| will cause the default `:' character to be treated as part of a field value and `|' becomes the field separator. Doing this may be useful in conjunction with a system that wants to use pam_access with X based applications, since the PAM_TTY item is likely to be of the form "hostname:0" which includes a `:' character in its value. But you should not need this.
-
listsep=separators -
This option modifies the list separator character that pam_access will recognize when parsing the access configuration file. For example: listsep=, will cause the default ` ' (space) and `\t' (tab) characters to be treated as part of a list element value and `,' becomes the only list element separator. Doing this may be useful on a system with group information obtained from a Windows domain, where the default built-in groups "Domain Users", "Domain Admins" contain a space.
-
nodefgroup -
User tokens which are not enclosed in parentheses will not be matched against the group database. The backwards compatible default is to try the group database match even for tokens not enclosed in parentheses.
- PAM_SUCCESS
-
Access was granted.
- PAM_PERM_DENIED
-
Access was not granted.
- PAM_IGNORE
-
pam_setcredwas called which does nothing. - PAM_ABORT
-
Not all relevant data or options could be gotten.
- PAM_USER_UNKNOWN
-
The user is not known to the system.
These are some example lines which might be specified in /etc/security/access.conf.
User root should be allowed to get access via cron, X11 terminal :0, tty1, ..., tty5, tty6.
+:root:crond :0 tty1 tty2 tty3 tty4 tty5 tty6
User root should be allowed to get access from hosts which own the IPv4 addresses. This does not mean that the connection have to be a IPv4 one, a IPv6 connection from a host with one of this IPv4 addresses does work, too.
+:root:192.168.200.1 192.168.200.4 192.168.200.9
+:root:127.0.0.1
User root should get access from network 192.168.201. where the term will be evaluated by string matching. But it might be better to use network/netmask instead. The same meaning of 192.168.201. is 192.168.201.0/24 or 192.168.201.0/255.255.255.0.
+:root:192.168.201.
User root should be able to have access from hosts foo1.bar.org and foo2.bar.org (uses string matching also).
+:root:foo1.bar.org foo2.bar.org
User root should be able to have access from domain foo.bar.org (uses string matching also).
+:root:.foo.bar.org
User root should be denied to get access from all other sources.
-:root:ALL
User foo and members of netgroup admins should be allowed to get access from all sources. This will only work if netgroup service is available.
+:@admins foo:ALL
User john and foo should get access from IPv6 host address.
+:john foo:2001:db8:0:101::1
User john should get access from IPv6 net/mask.
+:john:2001:db8:0:101::/64
Members of group wheel should be allowed to get access from all sources.
+:(wheel):ALL
Disallow console logins to all but the shutdown, sync and all other accounts, which are a member of the wheel group.
-:ALL EXCEPT (wheel) shutdown sync:LOCAL
All other users should be denied to get access from all sources.
-:ALL:ALL
The logdaemon style login access control scheme was designed and implemented by Wietse Venema. The pam_access PAM module was developed by Alexei Nogin <[email protected]>. The IPv6 support and the network(address) / netmask feature was developed and provided by Mike Becher <[email protected]>.
