From d2e727bf6826e486e9058877332860314c760df8 Mon Sep 17 00:00:00 2001
From: Mike Yuan <me@yhndnzj.com>
Date: Sun, 15 Jun 2025 19:13:22 +0200
Subject: [PATCH] hostname-util: do not allow empty machine spec

Follow-up for 2ae32e9d8fc95010ee4b52b3118ea9fbf05d96d6

Let's not open this up even further and rather disallow
--machine="".
---
 src/basic/hostname-util.c     | 16 ++++++++++++----
 src/test/test-hostname-util.c |  3 ++-
 2 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/src/basic/hostname-util.c b/src/basic/hostname-util.c
index 1372dec0b2f..047f0c07355 100644
--- a/src/basic/hostname-util.c
+++ b/src/basic/hostname-util.c
@@ -179,6 +179,8 @@ int split_user_at_host(const char *s, char **ret_user, char **ret_host) {
         /* Splits a user@host expression (one of those we accept on --machine= and similar). Returns NULL in
          * each of the two return parameters if that part was left empty. */
 
+        assert(s);
+
         const char *rhs = strchr(s, '@');
         if (rhs) {
                 if (ret_user && rhs > s) {
@@ -192,10 +194,16 @@ int split_user_at_host(const char *s, char **ret_user, char **ret_host) {
                         if (!h)
                                 return -ENOMEM;
                 }
-        } else if (!isempty(s) && ret_host) {
-                h = strdup(s);
-                if (!h)
-                        return -ENOMEM;
+
+        } else {
+                if (isempty(s))
+                        return -EINVAL;
+
+                if (ret_host) {
+                        h = strdup(s);
+                        if (!h)
+                                return -ENOMEM;
+                }
         }
 
         if (ret_user)
diff --git a/src/test/test-hostname-util.c b/src/test/test-hostname-util.c
index 4abac5ca3a9..b3e3b1b84a7 100644
--- a/src/test/test-hostname-util.c
+++ b/src/test/test-hostname-util.c
@@ -107,7 +107,8 @@ static void test_split_user_at_host_one(const char *s, const char *expected_user
 }
 
 TEST(split_user_at_host) {
-        test_split_user_at_host_one("", NULL, NULL, 0);
+        ASSERT_ERROR(split_user_at_host("", NULL, NULL), EINVAL);
+
         test_split_user_at_host_one("@", NULL, NULL, 1);
         test_split_user_at_host_one("a", NULL, "a", 0);
         test_split_user_at_host_one("a@b", "a", "b", 1);
-- 
2.47.3