libnss_tcb: Match interfaces with NSS documentation.

According to [1] the interfaces provided are of return-type 'enum nss_status',
of which the _nss_database_getXXX_r() interfaces are mandated to take four
parameters: a pointer to the result, a pointer to an additional buffer, the
size of the buffer supplied, and a pointer to an integer to report error
values (errnop).  The returned status values are meant to be accompanied by
a corresponding error value [2] passed through the errnop pointer.

[1] https://www.gnu.org/software/libc/manual/html_node/NSS-Module-Function-Internals.html
[2] https://www.gnu.org/software/libc/manual/html_node/NSS-Modules-Interface.html

Signed-off-by: Björn Esser <[email protected]>

Author: besser82

ChangeLog

@@ -1,5 +1,23 @@
 2024-12-20  Björn Esser  <besser82 at fedoraproject.org>
 
+	libnss_tcb: Match interfaces with NSS documentation.
+	According to [1] the interfaces provided are of return-type
+	'enum nss_status', of which the _nss_database_getXXX_r() interfaces
+	are mandated to take four parameters: a pointer to the result,
+	a pointer to an additional buffer, the size of the buffer supplied,
+	and a pointer to an integer to report error values (errnop).  The
+	returned status values are meant to be accompanied by a corresponding
+	error value [2] passed through the errnop pointer.
+	[1] https://www.gnu.org/software/libc/manual/html_node/NSS-Module-Function-Internals.html
+	[2] https://www.gnu.org/software/libc/manual/html_node/NSS-Modules-Interface.html
+	* libs/nss.c (_nss_tcb_setspent): Adapt return-type and use return
+	values from documented macro.
+	(_nss_tcb_endspent): Likewise.
+	(_nss_tcb_getspnam_r): Adapt return-type, change fourth parameter
+	to be 'int *errnop', use return values from documented macros, and
+	set proper errno in errnop before returning.
+	(_nss_tcb_getspent_r): Likewise.
+
 	libnss_tcb: Disallow potentially-malicious user names in getspnam(3).
 	IEEE Std 1003.1-2001 allows only the following characters to appear
 	in group- and usernames: letters, digits, underscores, periods,

libs/nss.c

@@ -13,27 +13,27 @@
 
 static __thread DIR *tcbdir = NULL;
 
-int _nss_tcb_setspent(void)
+enum nss_status _nss_tcb_setspent(void)
 {
 	if (!tcbdir) {
 		tcbdir = opendir(TCB_DIR);
 		if (!tcbdir)
 			return NSS_STATUS_UNAVAIL;
 
-		return 1;
+		return NSS_STATUS_SUCCESS;
 	}
 
 	rewinddir(tcbdir);
-	return 1;
+	return NSS_STATUS_SUCCESS;
 }
 
-int _nss_tcb_endspent(void)
+enum nss_status _nss_tcb_endspent(void)
 {
 	if (tcbdir) {
 		closedir(tcbdir);
 		tcbdir = NULL;
 	}
-	return 1;
+	return NSS_STATUS_SUCCESS;
 }
 
 /******************************************************************************
@@ -91,57 +91,80 @@ static FILE *tcb_safe_open(const char *file, const char *name)
 	return f;
 }
 
-int _nss_tcb_getspnam_r(const char *name, struct spwd *__result_buf,
-    char *__buffer, size_t __buflen, struct spwd **__result)
+enum nss_status _nss_tcb_getspnam_r(const char *name,
+    struct spwd *__result_buf, char *__buffer, size_t __buflen, int *__errnop)
 {
 	FILE *f;
 	char *file;
 	int retval, saved_errno;
 
 	/* Disallow potentially-malicious user names */
 	if (!is_valid_username(name)) {
-		errno = ENOENT;
+		/* we don't serve an entry here */
+		*__errnop = ENOENT;
 		return NSS_STATUS_NOTFOUND;
 	}
 
-	if (asprintf(&file, TCB_FMT, name) < 0)
+	if (asprintf(&file, TCB_FMT, name) < 0) {
+		/* retry, as malloc or another resource has failed */
+		*__errnop = EAGAIN;
 		return NSS_STATUS_TRYAGAIN;
+	}
+
 	f = tcb_safe_open(file, name);
 	free(file);
-	if (!f)
-		return errno == ENOENT ? NSS_STATUS_NOTFOUND : NSS_STATUS_UNAVAIL;
+	if (!f) {
+		/* $user/shadow not existing nor readable */
+		*__errnop = ENOENT;
+		return NSS_STATUS_UNAVAIL;
+	}
 
-	retval = fgetspent_r(f, __result_buf, __buffer, __buflen, __result);
+	retval = fgetspent_r(f, __result_buf, __buffer,
+	    __buflen, &__result_buf);
 	saved_errno = errno;
 	fclose(f);
 	errno = saved_errno;
-	if (!retval)
-		return NSS_STATUS_SUCCESS;
 
-	switch (saved_errno) {
+	/* real error number is retval from fgetspent_r(),
+	   by NSS spec errnop *MUST NOT* be set to 0 */
+	if (retval)
+		*__errnop = retval;
+
+	switch (retval) {
 	case 0:
+		/* no error, entry found */
 		return NSS_STATUS_SUCCESS;
 
 	case ENOENT:
+		/* if the file would not exist nor be readable, we would
+		   have already bailed out with ENOENT/NSS_STATUS_UNAVAIL
+		   immediately after the call to tcb_safe_open() */
 		return NSS_STATUS_NOTFOUND;
 
+	case EAGAIN:
+		/* ressources are temporary not available */
+		return NSS_STATUS_TRYAGAIN;
+
 	case ERANGE:
+		/* buffer too small */
 		return NSS_STATUS_TRYAGAIN;
 
 	default:
+		/* something else, e.g. parser error, but we can't help it */
 		return NSS_STATUS_UNAVAIL;
 	}
 }
 
-int _nss_tcb_getspent_r(struct spwd *__result_buf,
-    char *__buffer, size_t __buflen, struct spwd **__result)
+enum nss_status _nss_tcb_getspent_r(struct spwd *__result_buf,
+    char *__buffer, size_t __buflen, int *__errnop)
 {
 	struct dirent *result;
 	off_t currpos;
 	int retval, saved_errno;
 
 	if (!tcbdir) {
-		errno = ENOENT;
+		/* tcbdir does not exist */
+		*__errnop = ENOENT;
 		return NSS_STATUS_UNAVAIL;
 	}
 
@@ -154,21 +177,26 @@ int _nss_tcb_getspent_r(struct spwd *__result_buf,
 			closedir(tcbdir);
 			errno = saved_errno;
 			tcbdir = NULL;
+			/* cannot iterate tcbdir */
+			*__errnop = ENOENT;
 			return NSS_STATUS_UNAVAIL;
 		}
 		if (!result) {
 			closedir(tcbdir);
-			errno = ENOENT;
+			errno = saved_errno;
 			tcbdir = NULL;
+			/* we have no more entries in tcbdir */
+			*__errnop = ENOENT;
 			return NSS_STATUS_NOTFOUND;
 		}
 		errno = saved_errno;
 	} while (!strcmp(result->d_name, ".") ||
 	    !strcmp(result->d_name, "..") || result->d_name[0] == ':');
 
 	retval = _nss_tcb_getspnam_r(result->d_name, __result_buf, __buffer,
-	    __buflen, __result);
+	    __buflen, __errnop);
 
+	/* errnop has already been set by _nss_tcb_getspnam_r() */
 	switch (retval) {
 	case NSS_STATUS_SUCCESS:
 		return NSS_STATUS_SUCCESS;