libnss_tcb: Match interfaces with NSS documention.

According to [1] the interfaces provided should be of return-type
'enum nss_status', and take 'int *errnop' as the fourth (and last)
parameter.  Additionally the returned status values should be accompanied
by a corresponding ERRNO value [2] passed by 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 documention.
+	According to [1] the interfaces provided should be of return-type
+	'enum nss_status', and take 'int *errnop' as the fourth (and last)
+	parameter.  Additionally the returned status values should be
+	accompanied by a corresponding ERRNO value [2] passed by 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 macro, and
+	set proper errno in errnop before returning.  Also check the pointer
+	to result buffer, set by fgetspent_r(3), to be non-NULL.
+	(_nss_tcb_getspent_r): Likewise.
+	* include/attribute.h (TCB_FALLTHROUGH): New macro.
+
 	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,

include/attribute.h

@@ -26,4 +26,10 @@
 # define TCB_NONNULL(params)
 #endif
 
+#if TCB_GNUC_PREREQ(7,1)
+# define TCB_FALLTHROUGH __attribute__((fallthrough));
+#else
+# define TCB_FALLTHROUGH /* FALLTHRU */
+#endif
+
 #endif /* TCB_ATTRIBUTE_H_ */

libs/nss.c

@@ -9,31 +9,32 @@
 #include <fcntl.h>
 #include <dirent.h>
 
+#include "attribute.h"
 #include "tcb.h"
 
 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 +92,85 @@ 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;
+	struct spwd **result_buf_ptr = NULL;
 
 	/* 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 */
+		*__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_ptr);
 	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() */
+	switch (retval) {
 	case 0:
-		return NSS_STATUS_SUCCESS;
+		if (*result_buf_ptr)
+			return NSS_STATUS_SUCCESS;
+
+		/* else: no error, but entry not found;
+		   is properly handled by case ENOENT */
+		TCB_FALLTHROUGH
 
 	case ENOENT:
+		/* if the file would not exist, we would have already
+		   bailed out with ENOENT/NSS_STATUS_UNAVAIL immediately
+		   after the call to tcb_safe_open() */
+		*__errnop = ENOENT;
 		return NSS_STATUS_NOTFOUND;
 
+	case EAGAIN:
+		/* ressources are temporary not available */
+		*__errnop = EAGAIN;
+		return NSS_STATUS_TRYAGAIN;
+
 	case ERANGE:
+		/* __buffer too small */
+		*__errnop = ERANGE;
 		return NSS_STATUS_TRYAGAIN;
 
 	default:
+		/* something serious, but we can't help it */
+		*__errnop = retval;
 		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 +183,26 @@ 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;