getlogin_r: Make actually reentrant and fix error return value.

Fixes #18349.

src/system/libroot/posix/unistd/Jamfile

@@ -22,7 +22,7 @@ for architectureObject in [ MultiArchSubDirSetup ] {
 			exec.cpp
 			_exit.c
 			fork.c
-			getlogin.c
+			getlogin.cpp
 			getpagesize.c
 			hostname.cpp
 			ioctl.c

src/system/libroot/posix/unistd/getlogin.c

@@ -1,50 +0,0 @@
-/*
- * Copyright 2002-2006, Axel Dörfler, [email protected]. All rights reserved.
- * Distributed under the terms of the MIT License.
- */
-
-
-#include <syscalls.h>
-
-#include <errno.h>
-#include <stdio.h>
-#include <string.h>
-#include <unistd.h>
-#include <pwd.h>
-
-#include <errno_private.h>
-
-
-char *getlogin()
-{
-	struct passwd *pw;
-	pw = getpwuid(getuid());
-	if (pw)
-		return pw->pw_name;
-	__set_errno(ENOMEM);
-	return NULL;
-}
-
-
-int getlogin_r(char *name, size_t nameSize)
-{
-	struct passwd *pw;
-	pw = getpwuid(getuid());
-	if (pw && (nameSize >= LOGIN_NAME_MAX)) {
-		memset(name, 0, nameSize);
-		strlcpy(name, pw->pw_name, LOGIN_NAME_MAX);
-		return B_OK;
-	}
-	return ENOMEM;
-}
-
-
-char *
-cuserid(char *s)
-{
-	if (s != NULL && getlogin_r(s, L_cuserid))
-		return s;
-
-	return getlogin();
-}
-

src/system/libroot/posix/unistd/getlogin.cpp

@@ -0,0 +1,61 @@
+/*
+ * Copyright 2002-2006, Axel Dörfler, [email protected]. All rights reserved.
+ * Copyright 2023, Haiku, Inc. All rights reserved.
+ * Distributed under the terms of the MIT License.
+ */
+
+
+#include <syscalls.h>
+
+#include <errno.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+#include <pwd.h>
+
+#include <errno_private.h>
+#include <user_group.h>
+
+
+char*
+getlogin()
+{
+	struct passwd *pw;
+	pw = getpwuid(getuid());
+	if (pw)
+		return pw->pw_name;
+	__set_errno(ENOMEM);
+	return NULL;
+}
+
+
+int
+getlogin_r(char *name, size_t nameSize)
+{
+	struct passwd* pw = NULL;
+	struct passwd passwdBuffer;
+	char passwdStringBuffer[MAX_PASSWD_BUFFER_SIZE];
+
+	int status = getpwuid_r(getuid(), &passwdBuffer, passwdStringBuffer,
+		sizeof(passwdStringBuffer), &pw);
+	if (status != B_OK)
+		return status;
+
+	if (strnlen(pw->pw_name, LOGIN_NAME_MAX) >= nameSize)
+		return ERANGE;
+
+	memset(name, 0, nameSize);
+	strlcpy(name, pw->pw_name, LOGIN_NAME_MAX);
+	return B_OK;
+}
+
+
+char *
+cuserid(char *s)
+{
+	if (s != NULL && getlogin_r(s, L_cuserid))
+		return s;
+
+	return getlogin();
+}
+