275c2fc980
gain us anything to run as the user since an attacker can just have an setuid(0) in their egg. Running as root solves potential problems wrt signalling.
129 lines
5.2 KiB
Plaintext
129 lines
5.2 KiB
Plaintext
NOTE: the Sudo auth API is subject to change
|
|
|
|
Purpose: to provide a simple API for authentication methods that
|
|
encapsulates things nicely without turning into a maze
|
|
of #ifdef's
|
|
|
|
The sudo_auth struct looks like this:
|
|
|
|
typedef struct sudo_auth {
|
|
short flags; /* /* various flags, see below */
|
|
short status; /* status from verify routine */
|
|
char *name; /* name of the method in string form */
|
|
VOID *data; /* method-specific data pointer */
|
|
|
|
int (*init) __P((struct passwd *pw, char **prompt, sudo_auth *auth));
|
|
int (*setup) __P((struct passwd *pw, char **prompt, sudo_auth *auth));
|
|
int (*verify) __P((struct passwd *pw, char *p, sudo_auth *auth));
|
|
int (*cleanup) __P((struct passwd *pw, int status, sudo_auth *auth));
|
|
} sudo_auth;
|
|
|
|
The variables in the struct are as follows:
|
|
flags Bitwise binary flags, see below.
|
|
|
|
status Contains the return value from the last run of
|
|
the "verify" function. Starts out as AUTH_FAILURE.
|
|
|
|
name The name of the authentication method as a C string.
|
|
|
|
data A pointer to method-specific data. This is passed to
|
|
all the functions of an auth method and is usually
|
|
initialized in the "init" or "setup" routines.
|
|
|
|
Possible values of sudo_auth.flags:
|
|
FLAG_USER Whether or not the auth functions should run with
|
|
the euid of the invoking user instead of 0.
|
|
|
|
FLAG_CONFIGURED If set then the auth method is assumed to have been
|
|
configured successfully. All auth methods start out
|
|
with this set. If an "init" or "setup" function
|
|
fails, this bit is cleared.
|
|
|
|
FLAG_ONEANDONLY If set, this indicates that the method is the
|
|
only one in use. Can be used by auth functions
|
|
to determine whether to return a fatal or nonfatal
|
|
error.
|
|
|
|
The member functions can return the following values:
|
|
AUTH_SUCCESS Function succeeded. For a ``verify'' function
|
|
this means the user correctly authenticated.
|
|
|
|
AUTH_FAILURE Function failed. If this is an ``init'' or
|
|
``setup'' routine, the auth method will be
|
|
marked as !configured.
|
|
|
|
AUTH_FATAL A fatal error occurred. The routine should have
|
|
written an error message to stderr and optionally
|
|
sent mail to the administrator. (If log_error()
|
|
is called to do this, the NO_EXIT flag must be used.)
|
|
When verify_user() gets AUTH_FATAL from an auth
|
|
function it does an exit(1).
|
|
|
|
The functions in the struct are as follows:
|
|
|
|
int init(struct passwd *pw, char **prompt, sudo_auth *auth)
|
|
Function to do any one-time initialization for the auth
|
|
method. All of the "init" functions are run before anything
|
|
else. A pointer to the prompt string may be used to add
|
|
method-specific info to the prompt.
|
|
|
|
int setup(struct passwd *pw, char **prompt, sudo_auth *auth)
|
|
Function to do method-specific setup. All the "setup"
|
|
routines are run before any of the "verify" routines. A
|
|
pointer to the prompt string may be used to add method-specific
|
|
info to the prompt.
|
|
|
|
int verify(struct passwd *pw, char *p, sudo_auth *auth)
|
|
Function to do user verification for this auth method. For
|
|
standalone auth methods ``p'' is the prompt string. For
|
|
normal auth methods, ``p'' is the password the user entered.
|
|
Note that standalone auth methods are responsible for
|
|
rerading the password themselves.
|
|
|
|
int cleanup(struct passwd *pw, sudo_auth *auth)
|
|
Function to do per-auth method cleanup. This is only run
|
|
at the end of the authentication process, after the user
|
|
has completely failed or succeeded to authenticate.
|
|
The ``auth->status'' variable contains the result of the
|
|
last authentication attempt which may be interesting.
|
|
|
|
A note about standalone methods. Some authentication methods can't
|
|
coexist with any others. This may be because they encapsulate other
|
|
methods (pam, sia) or because they have a special way of interacting
|
|
with the user (securid).
|
|
|
|
Adding a new authentication method:
|
|
|
|
Each method should live in its own file. Add prototypes for the functions
|
|
in sudo_auth.h.
|
|
|
|
If this is a standalone method, add it to the standalone #if cascade
|
|
in sudo_auth.h. For instance, for a method, ``fooauth'', add:
|
|
|
|
#elif defined(HAVE_FOOAUTH)
|
|
# define AUTH_STANDALONE \
|
|
AUTH_ENTRY(0, "foo", \
|
|
foo_init, foo_setup, foo_verify, foo_cleanup)
|
|
|
|
If the method needs to run as the user, not root, replace the first
|
|
parameter to AUTH_ENTRY (0) with FLAG_USER. If you don't have a
|
|
init/setup/cleanup routine, just use a NULL for that field.
|
|
|
|
For a normal authentication method, add it to the ``auth_switch'' in
|
|
sudo_auth.c. If ``fooauth'' is a normal auth method, its entry
|
|
would look like:
|
|
|
|
# ifdef HAVE_FOOAUTH
|
|
AUTH_ENTRY(0, "foo", foo_init, foo_setup, foo_verify, foo_cleanup)
|
|
# endif
|
|
|
|
Again, if the method doesn't need to run as root, replace the 0 with
|
|
FLAG_USER. Likewise, if you don't have a init/setup/cleanup routine,
|
|
just use a NULL for that field.
|
|
|
|
NOTE: You should not make a method both ``standalone'' and
|
|
``normal''. Just use the --without-passwd configure argument
|
|
to disable passwd/shadow file checking and then have your
|
|
auth routines check the FLAG_ONEANDONLY flag to see if
|
|
they are running standalone and act accordingly.
|