NAME¶

lcmaps_posix_enf.mod - LCMAPS plugin to switch user identity

SYNOPSIS¶

lcmaps_posix_enf.mod [-maxuid number of uids] [-maxpgid number of primary gids] [-maxsgid number of secondary gids]

DESCRIPTION¶

The Posix Enforcement plugin will enforce (apply) the gathered credentials that are stacked in the datastructure of the Plugin Manager. The plugin will get the credential information that is gathered by one or more Acquisition plugins. This implies that at least one Acquisition should have been run prior to this Enforcement. All of the gathered information will be checked by looking into the 'passwd' file of the system (FIXME: shouldn't that be getpwent(2)?). These files have information about all registered system account and its user groups.

The Posix Enforcement plugin does not check whether the secondary groups have the primary UID as a member, so it is possible to end up with more group memberships than what is defined in the group database.

The (BSD/POSIX) functions setreuid(2), setregid(2) and setgroups(2) are used to change the privileges of the process from root to that of a local user.

OPTIONS¶

-maxuid number of uids

In principle, this will set the maximum number of allowed UIDs that this plugin will handle, but at the moment only the first UID found will be enforced; the others will discarded. By setting the value to a maximum there will be a failure raised when the amount of UIDs exceed the set maximum. Without this value the plugin will continue and will enforce only the first found value in the credential data structure.

-maxpgid number of primary gids

This will set the maximum number of allowed Primary GIDs that this plugin will handle, similar to -maxuid. Also here only the first primary GID found will be taken into account.

-maxsgid number of secondary gids

This will set the maximum allowed Secondary GIDs that this plugin will handle. This number is limited by the system (NGROUPS) and is usually 32. If the plugin cannot determine the system value, it limits itself to 32.

The remaining options are considered dangerous, as they have the potential to allow a client process to gain root privileges. The use of these options is strongly discouraged.

-set_only_euid {yes|no}

The result of setting this option to 'yes' is that only the effective uid is set. In other words, it is still possible to regain root (uid) privileges for the process. This is definitely undesirable if this module is used from a process like the gatekeeper, since it would be possible for user jobs to get root privileges.

-set_only_egid {yes|no}

Analogue to the previous option the result of setting this option to 'yes' is that only the effective (primary) gid is set. In other words, it is still possible to regain root (gid) privileges for the process. This is definitely undesirable if this module is used from a process like the gatekeeper, since it would be possible for user jobs to get root privileges. Possibly this option should be set if the module is used by gridFTP, since this service does not spawn user jobs and has to regain root pivileges at the end.

RETURN VALUES¶

LCMAPS_MOD_SUCCESS

Success.

LCMAPS_MOD_FAIL

Failure.

BUGS¶

Please report any errors to the Nikhef Grid Middleware Security Team <grid-mw-security-support@nikhef.nl>.

SEE ALSO¶

lcmaps.db(5), lcmaps(3), getpwent(3), getgrent(3), setreuid(2), setregid(2), setgroups(2).

AUTHORS¶

LCMAPS and the LCMAPS plug-ins were written by the Grid Middleware Security Team <grid-mw-security@nikhef.nl>.