login_getclass

LOGIN_CAP(3)                Library Functions Manual              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, login_setcryptfmt — functions for accessing the login
     class capabilities database

LIBRARY
     System Utilities Library (libutil, -lutil)

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);

     const char *
     login_getcapstr(login_cap_t *lc, const char *cap, const char *def,
         const char *error);

     const char **
     login_getcaplist(login_cap_t *lc, const char *cap, const char *chars);

     const char *
     login_getpath(login_cap_t *lc, const char *cap, const 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);

     const char *
     login_getstyle(login_cap_t *lc, const char *style, const char *auth);

     const char *
     login_setcryptfmt(login_cap_t *lc, const char *def, const char *error);

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(), or indirectly via a user's
     login record using login_getpwclass(), by class name using
     login_getclass().  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.

     The login_getclassbyname() function is the basic means to get a
     login_cap_t object.  It accepts two arguments: the first one, name, is
     the record identifier of the record to be retrieved; the second, pwd, is
     an optional pointer to a passwd structure.  First of all, its arguments
     are used by the function to choose between system and user modes of
     operation.  When in system mode, only the system login class database is
     used.  When in user mode, the supplemental login class database in the
     user's home directory is allowed to override settings from the system
     database in a limited way as noted below.  To minimize security
     implications, user mode is entered by login_getclassbyname() if and only
     if name is LOGIN_MECLASS (‘me’) and pwd is not NULL.  Otherwise system
     mode is chosen.

     In system mode, any record in the system database /etc/login.conf can be
     accessed, and a fallback to the default record is provided as follows.
     If name is NULL, an empty string, or a class that does not exist in the
     login class database, then the LOGIN_DEFCLASS record (‘default’) is
     returned instead.

     In user mode, only the LOGIN_MECLASS record (‘me’) is accessed and no
     fallback to the ‘default’ record is provided.  The directory specified by
     pwd->pw_dir is searched for a login database file called .login_conf, and
     only the ‘me’ capability record contained within it may override the
     system record with the same name while other records are ignored.  Using
     this scheme, an application can explicitly allow users to override a
     selected subset of login settings.  To do so, the application should
     obtain two login_cap_t objects, one in user mode and the other in system
     mode, and then query the user object before the system object for login
     parameters that are allowed to be overridden by the user.  For example,
     the user's .login_conf can provide a convenient way for a user to set up
     their preferred login environment before the shell is invoked on login if
     supported by login(1).

     Note that access to the /etc/login.conf and .login_conf files will only
     be performed subject to the security checks documented in _secure_path(3)
     for the uids 0 and pwd->pw_uid respectively.

     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_getclass(), login_getpwclass() 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() differs
     from login_getclass() in that it allows the default class for a super-
     user 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.  Essentially,
     login_getclass(name) is equivalent to login_getclassbyname(name, NULL)
     and login_getuserclass(pwd) to login_getclassbyname(LOGIN_MECLASS, pwd).

     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.  The login_close() function 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 terabytes.
                         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 lc 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
                             previous 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.

     login_setcryptfmt()
                         The login_setcryptfmt() function is used to set the
                         crypt(3) format using the passwd_format configuration
                         entry.  If no entry is found, def is taken to be used
                         as the fallback.  If calling crypt_set_format(3) on
                         the specifier fails, error is returned to indicate
                         this.

SEE ALSO
     login(1), crypt(3), getcap(3), login_class(3), login.conf(5), termcap(5)

                                 June 14, 2007