From 5feb65c5b1f75d376fc032ccd1cb87766c5185a9 Mon Sep 17 00:00:00 2001
From: Yu Watanabe <watanabe.yu+github@gmail.com>
Date: Wed, 19 Nov 2025 05:10:44 +0900
Subject: [PATCH] user-util: avoid double evaluation in STRERROR_USER/GROUP()

Follow-up for 6e6e96f628d352b56fd396cffb311f16839f78fb.
---
 src/basic/user-util.c | 20 ++++++++++++++++++++
 src/basic/user-util.h | 10 +++++-----
 2 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/src/basic/user-util.c b/src/basic/user-util.c
index 4b692076c84..5610abac94d 100644
--- a/src/basic/user-util.c
+++ b/src/basic/user-util.c
@@ -28,6 +28,26 @@
 #include "user-util.h"
 #include "utf8.h"
 
+#define DEFINE_STRERROR_ACCOUNT(type)                                   \
+        const char* strerror_##type(                                    \
+                        int errnum,                                     \
+                        char *buf,                                      \
+                        size_t buflen) {                                \
+                                                                        \
+                errnum = ABS(errnum);                                   \
+                switch (errnum) {                                       \
+                case ESRCH:                                             \
+                        return "Unknown " STRINGIFY(type);              \
+                case ENOEXEC:                                           \
+                        return "Not a system " STRINGIFY(type);         \
+                default:                                                \
+                        return strerror_r(errnum, buf, buflen);         \
+                }                                                       \
+        }
+
+DEFINE_STRERROR_ACCOUNT(user);
+DEFINE_STRERROR_ACCOUNT(group);
+
 bool uid_is_valid(uid_t uid) {
 
         /* Also see POSIX IEEE Std 1003.1-2008, 2016 Edition, 3.436. */
diff --git a/src/basic/user-util.h b/src/basic/user-util.h
index b7e71720a57..e2486e5a69c 100644
--- a/src/basic/user-util.h
+++ b/src/basic/user-util.h
@@ -20,11 +20,11 @@
 #define MAP_UID_MIN ((uid_t) 60514)
 #define MAP_UID_MAX ((uid_t) 60577)
 
-/* A helper to print an error message when user or group resolution fails.
- * Note that we can't use ({ … }) to define a temporary variable, so errnum is
- * evaluated multiple times. */
-#define STRERROR_USER(errnum) ((errnum) == -ESRCH ? "Unknown user" : (errnum) == -ENOEXEC ? "Not a system user" : STRERROR(errnum))
-#define STRERROR_GROUP(errnum) ((errnum) == -ESRCH ? "Unknown group" : (errnum) == -ENOEXEC ? "Not a system group" : STRERROR(errnum))
+/* A helper to print an error message when user or group resolution fails. */
+const char* strerror_user(int errnum, char *buf, size_t buflen);
+#define STRERROR_USER(errnum) strerror_user(errnum, (char[ERRNO_BUF_LEN]){}, ERRNO_BUF_LEN)
+const char* strerror_group(int errnum, char *buf, size_t buflen);
+#define STRERROR_GROUP(errnum) strerror_group(errnum, (char[ERRNO_BUF_LEN]){}, ERRNO_BUF_LEN)
 
 static inline bool ERRNO_IS_NEG_BAD_ACCOUNT(intmax_t r) {
         return IN_SET(r,
-- 
2.47.3