LOGIN_CAP(3) FreeBSD 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)
HISTORY
The functions login_close(), login_getcapbool(), login_getcaplist(),
login_getcapnum(), login_getcapstr(), login_getcapsize(),
login_getcaptime(), login_getclass(), login_getclassbyname(),
login_getpwclass(), login_getstyle(), login_getuserclass() and
login_setcryptfmt() first appeared in FreeBSD 2.1.5.
FreeBSD 13.1-RELEASE-p6 May 10, 2020 FreeBSD 13.1-RELEASE-p6
man2web Home...