BSD_AUTH(3) OpenBSD Programmer's Manual BSD_AUTH(3)NAME
auth_open, auth_call, auth_challenge, auth_check_change,
auth_check_expire, auth_clean, auth_close, auth_clrenv, auth_clroption,
auth_clroptions, auth_getitem, auth_getpwd, auth_getstate, auth_getvalue,
auth_set_va_list, auth_setdata, auth_setenv, auth_setitem,
auth_setoption, auth_setpwd, auth_setstate - interface to the BSD
auth_call(auth_session_t *as, char *path, ...);
auth_clroption(auth_session_t * as, char *name);
auth_getitem(auth_session_t *as, auth_item_t item);
struct passwd *
auth_getvalue(auth_session_t *as, char *what);
auth_set_va_list(auth_session_t *as, va_list ap);
auth_setdata(auth_session_t *as, void *ptr, size_t len);
auth_setitem(auth_session_t *as, auth_item_t item, char *value);
auth_setoption(auth_session_t *as, char *name, char *value);
auth_setpwd(auth_session_t *as, struct passwd *pwd);
auth_setstate(auth_session_t *as, int state);
These functions provide the lower level interface to the BSD
Authentication system. They all operate on a BSD Authentication session
pointer, as, which is returned by auth_open(). The session pointer must
be passed to all other BSD Authentication functions called. The
auth_open() function returns NULL if it was unable to allocate memory for
the session. The session is terminated by the auth_close() function,
which also sets any environment variables requested by the login script
(assuming the user was not rejected) or removes files created by the
login script if the authentication was not successful. It returns the
final state of the authentication request. A return value of 0 implies
the user was not authenticated. A non-zero return value is made up of 1
or more of the following values ORed together:
AUTH_OKAY The user was authenticated.
AUTH_ROOTOKAY The user was authenticated with a root instance.
AUTH_SECURE The user was authenticated via a mechanism which is not
subject to eavesdropping attacks (such as provided by
The full state of the session is returned by the auth_getstate()
function. In addition to the values above, it also may contain the bits:
AUTH_SILENT Do not report an error, the user was not authenticated
for access and was not expected to be. This is returned
by login scripts that allow changing of the user's
password, for instance. This value is stripped off for
AUTH_CHALLENGE The user was not authenticated for access and a
challenge was issued. The challenge should be displayed
to the user, a response retrieved, and the result
verified. This value is stripped off for normal
AUTH_EXPIRED The user's account has expired.
AUTH_PWEXPIRED The user's password has expired and needs to be changed.
A session may be cleaned by calling auth_clean(). This function removes
any files created by a login script in this session and clears all state
associated with this session, with the exception of the option settings.
It is not necessary to call auth_clean() if auth_close() is called.
The remaining functions are described in alphabetical order.
The fundamental function for doing BSD Authentication is auth_call(). In
addition to the pointer to the BSD Authentication session, it takes the
path The full path name of the login script to run. The call will
fail if path does not pass the requirements of the secure_path(3)
... The remaining arguments, which should be of type char * and
terminated with a NULL, are passed to the login script at the end
of the command line.
The auth_call() function, after verifying the path, creates a bi-
directional pipe (socketpair) which is located on file descriptor 3 for
the child (the login script). This is known as the ``back channel''.
The actual command line passed to the child is made up of 3 parts. The
parameters passed to auth_call() following path have appended to them any
arguments specified by the auth_set_va_list() function. These are
typically the variable arguments passed to the function that calls
auth_call(). Any option values set by the auth_setoption() function are
inserted between the first argument (the command name) and the second
argument with a preceding -v flag. The name and value are separated by
Once the login script has been spawned, any data specified by the
auth_setdata() is written to the back channel. Multiple blocks of data
may have been specified and they will be sent in the same order they were
specified. As the data is sent, the storage for the data is zeroed out
and then freed (the data is zeroed out since it may contain sensitive
information, such as a password). Once any data is written out,
auth_call() reads up to 8192 bytes of data from the back channel. The
state of the session is determined from this data (see login.conf(5) for
details). If the login script exits with a 0 and does not specify any
return state on the back channel, the state prior to the call to
auth_call() is retained.
Note that while auth_call() will zero out the copies it makes of
sensitive information, such as plain text passwords, after it is sent, it
is the responsibility of the caller to zero out the original copies of
this sensitive information. Due to the mechanics of the auth_call()
function, this data must be zeroed before auth_call() is called. The
safest place to zero out sensitive information is immediately after it
has been passed to auth_setdata().
The back channel data may also contain a file descriptor passed back from
the login script. If this is the case, the login script will first send
back the string ``fd'' to indicate that a file descriptor will be the
next data item. The file descriptor will be passed back to the next
invocation of the login script with a number specified by the -v fd
option. This is used to implement stateful challenge/response schemes
that require a persistent connection during the challenge and response.
The copy of the descriptor in the parent process is closed when the child
is running to prevent deadlock when file locking is used. The descriptor
is also closed by a call to auth_close() or auth_clean().
The data read from the back channel is also used by the auth_getvalue()
and auth_close() functions. Subsequent calls to auth_call() will cause
this data to be lost and overwritten with the new data read from the new
The environment passed to the login script by auth_call() only contains
two values: PATH and SHELL. The PATH is set to the default path (/bin
and /usr/bin) while the SHELL is set to the default system shell
The auth_challenge() function queries the login script defined by the
current style for a challenge for the user specified by name. (See below
for the setting of the style and name). It internally uses the
auth_call() function. The generated challenge is returned. NULL is
returned on error or if no challenge was generated. The challenge can
also be extracted by the auth_getchallenge() function, which simply
returns the last challenge generated for this session.
The auth_check_change() and auth_check_expire() functions check the
password expiration (change) and account expiration times. They return 0
if no change or expiration time is set for the account. They return a
negative value of how many seconds have passed since the password or
account expired. In this case the state of the session is marked with
either AUTH_PWEXPIRED or AUTH_EXPIRED as well as clearing any bits which
would indicate the authentication was successful. If the password or
account has not expired, they return the number of seconds left until the
account does expire. The return value of -1 can either indicate the
password or account just expired or that no password entry was set for
the current session.
The auth_clrenv() function clears any requests set by a login script for
environment variables to be set.
The auth_clroption() function clears the previously set option name.
The auth_clroptions() function clears all previously set options.
The auth_getitem() function returns the value of item. The item may be
AUTH_CHALLENGE The latest challenge, if any, set for the session.
AUTH_CLASS The class of the user, as defined by the
/etc/login.conf file. This value is not directly used
by BSD Authentication, rather, it is passed to the
login scripts for their possible use.
AUTH_INTERACTIVE If set to any value, then the session is tagged as
interactive. If not set, the session is not
interactive. When the value is requested it is always
either NULL or ``True''. The auth subroutines may
choose to provide additional information to standard
output or standard error when the session is
interactive. There is no functional change in the
operation of the subroutines.
AUTH_NAME The name of the user being authenticated. The name
should include the instance, if any, that is being
AUTH_SERVICE The service requesting the authentication. Initially
it is set to the default service which provides the
traditional interactive service.
AUTH_STYLE The style of authentication being performed, as defined
by the /etc/login.conf file. The style determines
which login script should actually be used.
The value returned points to private memory and should not be freed by
The auth_getvalue() function returns the value, if any, associated with
the specified internal variable what. These variables are set by login
scripts. When a new login script is run (by the auth_call() function)
the values from the previous login script are lost. (See login.conf(5)
for details on internal variables.)
The auth_set_va_list() function establishes a variable argument list to
be used by the auth_call() function. It is intended to be used by
functions which need to call auth_call() but take a variable number of
arguments themselves. Since the arguments are not copied, the call to
auth_call() must be placed within the scope of ap. The auth_call()
function will call va_end(3) on ap.
The auth_setdata() function makes a copy of len bytes of data pointed to
by ptr for use by auth_call(). The data will be passed on the back
channel to the next login script called.
The auth_setenv() function adds/deletes any environment variables
requested by the login script to the current environment.
The auth_setitem() function assigns value to the specified item. The
items are described above with the auth_getitem() function. In addition,
if value is NULL, the item is cleared. If value is NULL and item is
AUTH_ALL then all items are cleared.
The auth_setoption() function requests that the option name be set with
the value of value when a script is executed by auth_call(). The actual
arguments to the script will be placed at the beginning of the argument
vector. For each option two arguments will be issued: -v name=value.
The function auth_setpwd() establishes the password file entry for the
authentication session. If the name has already been set by
auth_setitem() then the pwd argument may be NULL, else it must be the
password entry to use.
The function auth_getpwd() retrieves the saved password file entry for
the authentication session. If no entry has been saved (either
explicitly via auth_setpwd() or implicitly via auth_check_expire() or
auth_check_change()) it returns NULL. Note that the memory containing
the password file entry is freed by a call to auth_close() or
The function auth_setstate() sets the sessions state to state. Typically
this is either AUTH_OKAY or 0.
SEE ALSOauthenticate(3), login_cap(3), pw_dup(3), login.conf(5)CAVEATS
The auth_check_change() and auth_check_expire() functions call getpwnam()
or getpwuid(), overwriting the static storage used by the getpwent(3)
family of routines. The calling program must either make a local copy of
the passwd struct pointer via the pw_dup(3) function or use the
auth_setpwd(3) function to copy the passwd struct into as.
OpenBSD 4.9 July 15, 2009 OpenBSD 4.9