LOGIN_CAP(3)

NAME
login_close, login_getcapbool, login_getcaplist, login_getcapnum, login_getcapstr, login_getcapsize, login_getcaptime, login_getclass, login_getclassbyname, login_getpwclass, login_getstyle, login_getuserclass - functions for accessing the login class capabilities database.

LIBRARY
libutil

SYNOPSIS
#include <sys/types.h>
#include <login_cap.h>
void
login_close(login_cap_t *lc);
login_cap_t *
login_getclassbyname(const char *nam, const struct passwd *pwd);
login_cap_t *
login_getclass(const char *nam);
login_cap_t *
login_getpwclass(const struct passwd *pwd);
login_cap_t *
login_getuserclass(const struct passwd *pwd);
char *
login_getcapstr(login_cap_t *lc, const char *cap, char *def, char *error);
char **
login_getcaplist(login_cap_t *lc, const char *cap, const char *chars);
char *
login_getpath(login_cap_t *lc, const char *cap, char *error);
rlim_t
login_getcaptime(login_cap_t *lc, const char *cap, rlim_t def, rlim_t error);
rlim_t
login_getcapnum(login_cap_t *lc, const char *cap, rlim_t def, rlim_t error);
rlim_t
login_getcapsize(login_cap_t *lc, const char *cap, rlim_t def, rlim_t error);
int
login_getcapbool(login_cap_t *lc, const char *cap, int def);
char *
login_getstyle(login_cap_t *lc, char *style, const char *auth);

DESCRIPTION
These functions represent a programming interface to the login classes database provided in login.conf(5). This database contains capabilities, attributes and default environment and accounting settings for users and programs running as specific users, as determined by the login class field within entries in /etc/master.passwd.

Entries in login.conf(5) consist of colon ‘’: separated fields, the first field in each record being one or more identifiers for the record (which must be unique for the entire database), each separated by a '|', and may optionally include a description as the last 'name'. Remaining fields in the record consist of keyword/data pairs. Long lines may be continued with a backslash within empty entries, with the second and subsequent lines optionally indented for readability. This is similar to the format used in termcap(5), except that keywords are not limited to two significant characters, and are usually longer for improved readability. As with termcap entries, multiple records can be linked together (one record including another) using a field containing tc=<recordid>. The result is that the entire record referenced by <recordid> replaces the tc= field at the point at which it occurs. See getcap(3) for further details on the format and use of a capabilities database.

The login_cap interface provides a convenient means of retrieving login class records with all tc= references expanded. A program will typically call one of login_getclass(), login_getpwclass(), login_getuserclass() or login_getclassbyname() according to its requirements. Each of these functions returns a login capabilities structure, login_cap_t, which may subsequently be used to interrogate the database for specific values using the rest of the API. Once the login_cap_t is of no further use, the login_close() function should be called to free all resources used.

The structure of login_cap_t is defined in login_cap.h, as:

    typedef struct {
    	char *lc_class;
    	char *lc_cap;
    	char *lc_style;
    } login_cap_t;

The lc_class member contains a pointer to the name of the login class retrieved. This may not necessarily be the same as the one requested, either directly via login_getclassbyname(), indirectly via a user's login record using login_getpwclass(), by class name using login_getclass(), or login_getuserclass(). If the referenced user has no login class specified in /etc/master.passwd, the class name is NULL or an empty string. If the class specified does not exist in the database, each of these functions will search for a record with an id of "default", with that name returned in the lc_class field. In addition, if the referenced user has a UID of 0 (normally, "root", although the user name is not considered) then login_getpwclass() will search for a record with an id of "root" before it searches for the record with the id of "default".

The lc_cap field is used internally by the library to contain the expanded login capabilities record. Programs with unusual requirements may wish to use this with the lower-level getcap() style functions to access the record directly.

The lc_style field is set by the login_getstyle() function to the authorisation style, according to the requirements of the program handling a login itself.

As noted above, the get*class() functions return a login_cap_t object which is used to access the matching or default record in the capabilities database. getclassbyname() accepts two arguments: the first one is the record identifier of the record to be retrieved, the second is an optional directory name. If the first name argument is NULL, an empty string, or a class that does not exist in the supplemental or system login class database, then the system default record is returned instead. If the second dir parameter is NULL, then only the system login class database is used, but when not NULL, the named directory is searched for a login database file called ".login_conf", and capability records contained within it may override the system defaults. This scheme allows users to override some login settings from those in the system login class database by creating class records for their own private class with a record id of `me'. In the context of a login, it should be noted that some options cannot by overridden by users for two reasons; many options, such as resource settings and default process priorities, require root privileges in order to take effect, and other fields in the user's file are not be consulted at all during the early phases of login for security or administrative reasons. See login.conf(5) for more information on which settings a user is able to override. Typically, these are limited purely to the user's default login environment which might otherwise have been overridden in shell startup scripts in any case. The user's .login_conf merely provides a convenient way for a user to set up their preferred login environment before the shell is invoked on login.

If the specified record is NULL, empty or does not exist, and the system has no "default" record available to fall back to, there is a memory allocation error or for some reason cgetent(3) is unable to access the login capabilities database, this function returns NULL.

The functions login_getpwclass(), login_getclass() and login_getuserclass() retrieve the applicable login class record for the user's passwd entry or class name by calling login_getclassbyname(). On failure, NULL is returned. The difference between these functions is that login_getuserclass() includes the user's overriding .login_conf that exists in the user's home directory, and login_getpwclass() and login_getclass() restrict lookup only to the system login class database in /etc/login.conf. As explained earlier, login_getpwclass() only differs from login_getclass() in that it allows the default class for user 'root' as "root" if none has been specified in the password database. Otherwise, if the passwd pointer is NULL, or the user record has no login class, then the system "default" entry is retrieved.

Once a program no longer wishes to use a login_cap_t object, login_close() may be called to free all resources used by the login class. login_close() may be passed a NULL pointer with no harmful side-effects.

The remaining functions may be used to retrieve individual capability records. Each function takes a login_cap_t object as its first parameter, a capability tag as the second, and remaining parameters being default and error values that are returned if the capability is not found. The type of the additional parameters passed and returned depend on the type of capability each deals with, be it a simple string, a list, a time value, a file or memory size value, a path (consisting of a colon-separated list of directories) or a boolean flag. The manpage for login.conf(5) deals in specific tags and their type.

Note that with all functions in this group, you should not call free(3) on any pointers returned. Memory allocated during retrieval or processing of capability tags is automatically reused by subsequent calls to functions in this group, or deallocated on calling login_close().

login_getcapstr()
    This function returns a simple string capability. If the string is not found, then the value in def is returned as the default value, or if an error occurs, the value in the error parameter is returned.

login_getcaplist()
    This function returns the value corresponding to the named capability tag as a list of values in a NULL terminated array. Within the login class database, some tags are of type list, which consist of one or more comma- or space separated values. Usually, this function is not called directly from an application, but is used indirectly via login_getstyle().

login_getpath()
    This function returns a list of directories separated by colons ‘&:’. Capability tags for which this function is called consist of a list of directories separated by spaces.

login_getcaptime()
    This function returns a time value associated with a particular capability tag with the value expressed in seconds (the default), minutes, hours, days, weeks or (365 day) years or any combination of these. A suffix determines the units used: S for seconds, M for minutes, H for hours, D for days, W for weeks and Y for 365 day years. Case of the units suffix is ignored.

    Time values are normally used for setting resource, accounting and session limits. If supported by the operating system and compiler (which is true of FreeBSD ), the value returned is a quad (long long), of type rlim_t. A value "inf" or "infinity" may be used to express an infinite value, in which case RLIM_INFINITY is returned.

login_getcapnum()
    This function returns a numeric value for a tag, expressed either as tag=<value> or the standard cgetnum() format tag#<value>. The first format should be used in preference to the second, the second format is provided for compatibility and consistency with the getcap(3) database format where numeric types use the ‘#’ as the delimiter for numeric values. If in the first format, then the value given may be "inf" or "infinity" which results in a return value of RLIM_INFINITY. If the given capability tag cannot be found, the def parameter is returned, and if an error occurs, the error parameter is returned.

login_getcapsize()
    login_getcapsize() returns a value representing a size (typically, file or memory) which may be expressed as bytes (the default), 512 byte blocks, kilobytes, megabytes, gigabytes, and on systems that support the long long type, terabytes. The suffix used determines the units, and multiple values and units may be used in combination (e.g. 1m500k = 1.5 megabytes). A value with no suffix is interpreted as bytes, B as 512-byte blocks, K as kilobytes, M as megabytes, G as gigabytes and T as terrabytes. Case is ignored. The error value is returned if there is a login capabilities database error, if an invalid suffix is used, or if a numeric value cannot be interpreted.

login_getcapbool()
    This function returns a boolean value tied to a particular flag. It returns 0 if the given capability tag is not present or is negated by the presence of a "tag@" (See getcap(3) for more information on boolean flags), and returns 1 if the tag is found.

login_getstyle()
    This function is used by the login authorisation system to determine the style of login available in a particular case. The function accepts three parameters, the login_cap entry itself and two optional parameters, and authorisation type 'auth' and 'style', and applies these to determine the authorisation style that best suites these rules.

    •   If 'auth' is neither NULL nor an empty string, look for a tag of type "auth-<auth>" in the capability record. If not present, then look for the default tag "auth=".

    •   If no valid authorisation list was found from the previous step, then default to "passwd" as the authorisation list.

    •   If 'style' is not NULL or empty, look for it in the list of authorisation methods found from the pprevious step. If 'style' is NULL or an empty string, then default to "passwd" authorisation.

    •   If 'style' is found in the chosen list of authorisation methods, then return that, otherwise return NULL.

    This scheme allows the administrator to determine the types of authorisation methods accepted by the system, depending on the means by which the access occurs. For example, the administrator may require skey or kerberos as the authentication method used for access to the system via the network, and standard methods via direct dialup or console logins, significantly reducing the risk of password discovery by "snooping" network packets.

SEE ALSO
getcap(3), login_class(3), login.conf(5), termcap(5)