Push non-interactive mode checking down into the auth methods.

For "sudo -n" we only want to reject a command if user input is
actually required.  In the case of PAM at least, we may not need
to interact with the user.  Bug #956, GitHub issue #83

plugins/sudoers/auth/API

@@ -45,6 +45,10 @@ Possible values of sudo_auth.flags:
 			to determine whether to return a fatal or nonfatal
 			error.
 
+    FLAG_NONINTERACTIVE	If set, this indicates that the user invoked
+			sudo with the -n option and no user interaction
+			is allowed.
+
 The member functions can return the following values:
     AUTH_SUCCESS	Function succeeded.  For a ``verify'' function
 			this means the user correctly authenticated.
@@ -59,6 +63,14 @@ The member functions can return the following values:
 			When verify_user() gets AUTH_FATAL from an auth
 			function it does an exit(1).
 
+    AUTH_INTR		An attempt to read the password read was interrupted.
+			Usually this means the user entered ^C at the
+			password prompt.
+
+    AUTH_NONINTERACTIVE	Function failed because user interaction was
+			required but sudo was run in non-interactive
+			mode.
+
 The functions in the struct are as follows:
 
     int init(struct passwd *pw, sudo_auth *auth)

plugins/sudoers/auth/afs.c

@@ -50,6 +50,9 @@ sudo_afs_verify(struct passwd *pw, char *pass, sudo_auth *auth, struct sudo_conv
     struct ktc_token afs_token;
     debug_decl(sudo_afs_verify, SUDOERS_DEBUG_AUTH);
 
+    if (IS_NONINTERACTIVE(auth))
+	debug_return_int(AUTH_NONINTERACTIVE);
+
     /* Try to just check the password */
     ka_StringToKey(pass, NULL, &afs_key);
     if (ka_GetAdminToken(pw->pw_name,		/* name */

plugins/sudoers/auth/aix_auth.c

@@ -236,6 +236,9 @@ sudo_aix_verify(struct passwd *pw, char *prompt, sudo_auth *auth, struct sudo_co
     int ret = AUTH_SUCCESS;
     debug_decl(sudo_aix_verify, SUDOERS_DEBUG_AUTH);
 
+    if (IS_NONINTERACTIVE(auth))
+        debug_return_int(AUTH_NONINTERACTIVE);
+
     do {
 	pass = auth_getpass(prompt, SUDO_CONV_PROMPT_ECHO_OFF, callback);
 	if (pass == NULL)

plugins/sudoers/auth/bsdauth.c

@@ -114,6 +114,9 @@ bsdauth_verify(struct passwd *pw, char *prompt, sudo_auth *auth, struct sudo_con
     auth_session_t *as = ((struct bsdauth_state *) auth->data)->as;
     debug_decl(bsdauth_verify, SUDOERS_DEBUG_AUTH);
 
+    if (IS_NONINTERACTIVE(auth))
+        debug_return_int(AUTH_NONINTERACTIVE);
+
     /* save old signal handler */
     sigemptyset(&sa.sa_mask);
     sa.sa_flags = SA_RESTART;

plugins/sudoers/auth/dce.c

@@ -68,6 +68,9 @@ sudo_dce_verify(struct passwd *pw, char *plain_pw, sudo_auth *auth, struct sudo_
     error_status_t		status;
     debug_decl(sudo_dce_verify, SUDOERS_DEBUG_AUTH);
 
+    if (IS_NONINTERACTIVE(auth))
+	debug_return_int(AUTH_NONINTERACTIVE);
+
     /*
      * Create the local context of the DCE principal necessary
      * to perform authenticated network operations.  The network

plugins/sudoers/auth/fwtk.c

@@ -54,6 +54,9 @@ sudo_fwtk_init(struct passwd *pw, sudo_auth *auth)
     if (auth->data != NULL)
 	debug_return_int(AUTH_SUCCESS);
 
+    if (IS_NONINTERACTIVE(auth))
+        debug_return_int(AUTH_NONINTERACTIVE);
+
     if ((confp = cfg_read("sudo")) == (Cfg *)-1) {
 	sudo_warnx("%s", U_("unable to read fwtk config"));
 	debug_return_int(AUTH_FATAL);

plugins/sudoers/auth/pam.c

@@ -92,6 +92,7 @@ static struct sudo_conv_callback *conv_callback;
 static struct pam_conv pam_conv = { converse, &conv_callback };
 static char *def_prompt = PASSPROMPT;
 static bool getpass_error;
+static bool noninteractive;
 static pam_handle_t *pamh;
 static struct conv_filter *conv_filter;
 
@@ -203,6 +204,9 @@ sudo_pam_init2(struct passwd *pw, sudo_auth *auth, bool quiet)
 	debug_return_int(AUTH_SUCCESS);
     }
 
+    /* Stash value of noninteractive flag for conversation function. */
+    noninteractive = IS_NONINTERACTIVE(auth);
+
     /* Initial PAM. */
     pam_service = ISSET(sudo_mode, MODE_LOGIN_SHELL) ?
 	def_pam_login_service : def_pam_service;
@@ -321,7 +325,7 @@ sudo_pam_verify(struct passwd *pw, char *prompt, sudo_auth *auth, struct sudo_co
 
     if (getpass_error) {
 	/* error or ^C from tgetpass() */
-	debug_return_int(AUTH_INTR);
+	debug_return_int(noninteractive ? AUTH_NONINTERACTIVE : AUTH_INTR);
     }
     switch (*pam_status) {
 	case PAM_SUCCESS:
@@ -707,6 +711,13 @@ converse(int num_msg, PAM_CONST struct pam_message **msg,
 		if (getpass_error)
 		    goto done;
 
+		/* Treat non-interactive mode as a getpass error. */
+		if (noninteractive) {
+		    getpass_error = true;
+		    ret = PAM_CONV_ERR;
+		    goto done;
+		}
+
 		/* Choose either the sudo prompt or the PAM one. */
 		prompt = use_pam_prompt(pm->msg) ? pm->msg : def_prompt;
 

plugins/sudoers/auth/securid5.c

@@ -67,6 +67,9 @@ sudo_securid_init(struct passwd *pw, sudo_auth *auth)
     if (auth->data != NULL)
 	debug_return_int(AUTH_SUCCESS);
 
+    if (IS_NONINTERACTIVE(auth))
+        debug_return_int(AUTH_NONINTERACTIVE);
+
     /* Start communications */
     if (AceInitialize() == SD_FALSE) {
 	sudo_warnx("%s", U_("failed to initialise the ACE API library"));

plugins/sudoers/auth/sia.c

@@ -83,6 +83,9 @@ sudo_sia_verify(struct passwd *pw, char *prompt, sudo_auth *auth,
     int rc;
     debug_decl(sudo_sia_verify, SUDOERS_DEBUG_AUTH);
 
+    if (IS_NONINTERACTIVE(auth))
+        debug_return_int(AUTH_NONINTERACTIVE);
+
     /* Get password, return AUTH_INTR if we got ^C */
     pass = auth_getpass(prompt, SUDO_CONV_PROMPT_ECHO_OFF, callback);
     if (pass == NULL)

plugins/sudoers/auth/sudo_auth.c

@@ -98,7 +98,7 @@ static bool standalone;
  * Returns 0 on success and -1 on error.
  */
 int
-sudo_auth_init(struct passwd *pw)
+sudo_auth_init(struct passwd *pw, int mode)
 {
     sudo_auth *auth;
     int status = AUTH_SUCCESS;
@@ -109,6 +109,8 @@ sudo_auth_init(struct passwd *pw)
 
     /* Initialize auth methods and unconfigure the method if necessary. */
     for (auth = auth_switch; auth->name; auth++) {
+	if (ISSET(mode, MODE_NONINTERACTIVE))
+	    SET(auth->flags, FLAG_NONINTERACTIVE);
 	if (auth->init && !IS_DISABLED(auth)) {
 	    /* Disable if it failed to init unless there was a fatal error. */
 	    status = (auth->init)(pw, auth);
@@ -297,6 +299,8 @@ verify_user(struct passwd *pw, char *prompt, int validated,
 		status = (auth->setup)(pw, &prompt, auth);
 		if (status == AUTH_FAILURE)
 		    SET(auth->flags, FLAG_DISABLED);
+		else if (status == AUTH_NONINTERACTIVE)
+		    goto done;
 		else if (status == AUTH_FATAL || user_interrupted())
 		    goto done;		/* assume error msg already printed */
 	    }
@@ -310,6 +314,10 @@ verify_user(struct passwd *pw, char *prompt, int validated,
 
 	/* Get the password unless the auth function will do it for us */
 	if (!standalone) {
+	    if (IS_NONINTERACTIVE(auth_switch)) {
+		status = AUTH_NONINTERACTIVE;
+		goto done;
+	    }
 	    pass = auth_getpass(prompt, SUDO_CONV_PROMPT_ECHO_OFF, callback);
 	    if (pass == NULL)
 		break;
@@ -344,10 +352,13 @@ done:
 	case AUTH_INTR:
 	case AUTH_FAILURE:
 	    if (ntries != 0)
-		validated |= FLAG_BAD_PASSWORD;
+		SET(validated, FLAG_BAD_PASSWORD);
 	    log_auth_failure(validated, ntries);
 	    ret = false;
 	    break;
+	case AUTH_NONINTERACTIVE:
+	    SET(validated, FLAG_NO_USER_INPUT);
+	    FALLTHROUGH;
 	case AUTH_FATAL:
 	default:
 	    log_auth_failure(validated, 0);

plugins/sudoers/auth/sudo_auth.h

@@ -20,10 +20,11 @@
 #define SUDO_AUTH_H
 
 /* Auth function return values.  */
-#define AUTH_SUCCESS	0
+#define AUTH_SUCCESS		0
-#define AUTH_FAILURE	1
+#define AUTH_FAILURE		1
-#define AUTH_INTR	2
+#define AUTH_INTR		2
-#define AUTH_FATAL	3
+#define AUTH_FATAL		3
+#define AUTH_NONINTERACTIVE	4
 
 typedef struct sudo_auth {
     int flags;			/* various flags, see below */
@@ -40,14 +41,16 @@ typedef struct sudo_auth {
 } sudo_auth;
 
 /* Values for sudo_auth.flags.  */
-#define FLAG_DISABLED	0x02	/* method disabled */
+#define FLAG_DISABLED		0x02	/* method disabled */
-#define FLAG_STANDALONE	0x04	/* standalone auth method */
+#define FLAG_STANDALONE		0x04	/* standalone auth method */
-#define FLAG_ONEANDONLY	0x08	/* one and only auth method */
+#define FLAG_ONEANDONLY		0x08	/* one and only auth method */
+#define FLAG_NONINTERACTIVE	0x10	/* no user input allowed */
 
 /* Shortcuts for using the flags above. */
 #define IS_DISABLED(x)		((x)->flags & FLAG_DISABLED)
 #define IS_STANDALONE(x)	((x)->flags & FLAG_STANDALONE)
 #define IS_ONEANDONLY(x)	((x)->flags & FLAG_ONEANDONLY)
+#define IS_NONINTERACTIVE(x)	((x)->flags & FLAG_NONINTERACTIVE)
 
 /* Like tgetpass() but uses conversation function */
 char *auth_getpass(const char *prompt, int type, struct sudo_conv_callback *callback);

plugins/sudoers/check.c

@@ -125,13 +125,6 @@ check_user_interactive(int validated, int mode, struct getpass_closure *closure)
 	FALLTHROUGH;
 
     default:
-	/* Bail out if we are non-interactive and a password is required */
-	if (ISSET(mode, MODE_NONINTERACTIVE)) {
-	    validated |= FLAG_NON_INTERACTIVE;
-	    log_auth_failure(validated, 0);
-	    goto done;
-	}
-
 	/* XXX - should not lecture if askpass helper is being used. */
 	lectured = display_lecture(closure->tstat);
 
@@ -170,7 +163,7 @@ check_user(int validated, int mode)
      */
     if ((closure.auth_pw = get_authpw(mode)) == NULL)
 	goto done;
-    if (sudo_auth_init(closure.auth_pw) == -1)
+    if (sudo_auth_init(closure.auth_pw, mode) == -1)
 	goto done;
 
     /*

plugins/sudoers/logging.c

@@ -435,7 +435,7 @@ log_auth_failure(int status, unsigned int tries)
     audit_failure(NewArgv, "%s", N_("authentication failure"));
 
     /* If sudoers denied the command we'll log that separately. */
-    if (!ISSET(status, FLAG_BAD_PASSWORD|FLAG_NON_INTERACTIVE))
+    if (!ISSET(status, FLAG_BAD_PASSWORD|FLAG_NO_USER_INPUT))
 	logit = false;
 
     /*

plugins/sudoers/sudoers.h

@@ -157,7 +157,7 @@ struct sudo_user {
 #define FLAG_NO_USER		0x020
 #define FLAG_NO_HOST		0x040
 #define FLAG_NO_CHECK		0x080
-#define FLAG_NON_INTERACTIVE	0x100
+#define FLAG_NO_USER_INPUT	0x100
 #define FLAG_BAD_PASSWORD	0x200
 
 /*
@@ -297,7 +297,7 @@ bool sudo_auth_needs_end_session(void);
 int verify_user(struct passwd *pw, char *prompt, int validated, struct sudo_conv_callback *callback);
 int sudo_auth_begin_session(struct passwd *pw, char **user_env[]);
 int sudo_auth_end_session(struct passwd *pw);
-int sudo_auth_init(struct passwd *pw);
+int sudo_auth_init(struct passwd *pw, int mode);
 int sudo_auth_approval(struct passwd *pw, int validated, bool exempt);
 int sudo_auth_cleanup(struct passwd *pw, bool force);