Pluggable Authentication Modules
Prev |  | Next

# B. Sample PAM Module

The following is a minimal implementation of pam_unix(8), offering only authentication services. It should build and run with most PAM implementations, but takes advantage of OpenPAM extensions if available: note the use of pam_get_authtok(3), which enormously simplifies prompting the user for a password.

    #include <sys/param.h>

    #include <pwd.h>
    #include <stdlib.h>
    #include <stdio.h>
    #include <string.h>
    #include <unistd.h>

    #include <security/pam_modules.h>
    #include <security/pam_appl.h>

    #ifndef _OPENPAM
    static char password_prompt[] = "Password:";
    #endif

    #ifndef PAM_EXTERN
    #define PAM_EXTERN
    #endif

    PAM_EXTERN int
    pam_sm_authenticate(pam_handle_t *pamh, int flags,
    	int argc, const char *argv[])
    {
    #ifndef _OPENPAM
    	struct pam_conv *conv;
    	struct pam_message msg;
    	const struct pam_message *msgp;
    	struct pam_response *resp;
    #endif
    	struct passwd *pwd;
    	const char *user;
    	char *crypt_password, *password;
    	int pam_err, retry;

    	/* identify user */
    	if ((pam_err = pam_get_user(pamh, &user, NULL)) != PAM_SUCCESS)
    		return (pam_err);
    	if ((pwd = getpwnam(user)) == NULL)
    		return (PAM_USER_UNKNOWN);

    	/* get password */
    #ifndef _OPENPAM
    	pam_err = pam_get_item(pamh, PAM_CONV, (const void **)&conv);
    	if (pam_err != PAM_SUCCESS)
    		return (PAM_SYSTEM_ERR);
    	msg.msg_style = PAM_PROMPT_ECHO_OFF;
    	msg.msg = password_prompt;
    	msgp = &msg;
    #endif
    	for (retry = 0; retry < 3; ++retry) {
    #ifdef _OPENPAM
    		pam_err = pam_get_authtok(pamh, PAM_AUTHTOK,
    		    (const char **)&password, NULL);
    #else
    		resp = NULL;
    		pam_err = (*conv->conv)(1, &msgp, &resp, conv->appdata_ptr);
    		if (resp != NULL) {
    			if (pam_err == PAM_SUCCESS)
    				password = resp->resp;
    			else
    				free(resp->resp);
    			free(resp);
    		}
    #endif
    		if (pam_err == PAM_SUCCESS)
    			break;
    	}
    	if (pam_err == PAM_CONV_ERR)
    		return (pam_err);
    	if (pam_err != PAM_SUCCESS)
    		return (PAM_AUTH_ERR);

    	/* compare passwords */
    	if ((!pwd->pw_passwd[0] && (flags & PAM_DISALLOW_NULL_AUTHTOK)) ||
    	    (crypt_password = crypt(password, pwd->pw_passwd)) == NULL ||
    	    strcmp(crypt_password, pwd->pw_passwd) != 0)
    		pam_err = PAM_AUTH_ERR;
    	else
    		pam_err = PAM_SUCCESS;
    #ifndef _OPENPAM
    	free(password);
    #endif
    	return (pam_err);
    }

    PAM_EXTERN int
    pam_sm_setcred(pam_handle_t *pamh, int flags,
    	int argc, const char *argv[])
    {

    	return (PAM_SUCCESS);
    }

    PAM_EXTERN int
    pam_sm_acct_mgmt(pam_handle_t *pamh, int flags,
    	int argc, const char *argv[])
    {

    	return (PAM_SUCCESS);
    }

    PAM_EXTERN int
    pam_sm_open_session(pam_handle_t *pamh, int flags,
    	int argc, const char *argv[])
    {

    	return (PAM_SUCCESS);
    }

    PAM_EXTERN int
    pam_sm_close_session(pam_handle_t *pamh, int flags,
    	int argc, const char *argv[])
    {

    	return (PAM_SUCCESS);
    }

    PAM_EXTERN int
    pam_sm_chauthtok(pam_handle_t *pamh, int flags,
    	int argc, const char *argv[])
    {

    	return (PAM_SERVICE_ERR);
    }

    #ifdef PAM_MODULE_ENTRY
    PAM_MODULE_ENTRY("pam_unix");
    #endif

Prev | Home | Next
Sample PAM Application |  | Sample PAM Conversation Function