user-record: don't synthesize default list of self-modfiable fields for non-regular users. (#35133)

A follow-up for a192250eda

/cc @AdrianVovk

src/shared/user-record-show.c

@@ -28,21 +28,28 @@ const char* user_record_state_color(const char *state) {
         return NULL;
 }
 
-static void dump_self_modifiable(const char *heading, char **field, const char **value) {
+static void dump_self_modifiable(
+                const char *heading,
+                char **field,
+                const char **value) {
+
         assert(heading);
 
         /* Helper function for printing the various self_modifiable_* fields from the user record */
 
-        if (strv_isempty((char**) value))
-                /* Case 1: the array is explicitly set to be empty by the administrator */
-                printf("%13s %sDisabled by Administrator%s\n", heading, ansi_highlight_red(), ansi_normal());
+        if (!value)
+                /* Case 1: no value is set and no default either */
+                printf("%13s %snone%s\n", heading, ansi_highlight(), ansi_normal());
+        else if (strv_isempty((char**) value))
+                /* Case 2: the array is explicitly set to empty by the administrator */
+                printf("%13s %sdisabled by administrator%s\n", heading, ansi_highlight_red(), ansi_normal());
         else if (!field)
-                /* Case 2: we have values, but the field is NULL. This means that we're using the defaults.
+                /* Case 3: we have values, but the field is NULL. This means that we're using the defaults.
                  * We list them anyways, because they're security-sensitive to the administrator */
                 STRV_FOREACH(i, value)
                         printf("%13s %s%s%s\n", i == value ? heading : "", ansi_grey(), *i, ansi_normal());
         else
-                /* Case 3: we have a list provided by the administrator */
+                /* Case 4: we have a list provided by the administrator */
                 STRV_FOREACH(i, value)
                         printf("%13s %s\n", i == value ? heading : "", *i);
 }

src/shared/user-record.c

@@ -2165,8 +2165,15 @@ const char** user_record_self_modifiable_fields(UserRecord *h) {
 
         assert(h);
 
+        /* Note: if the self_modifiable_fields field in UserRecord is NULL we'll apply a default, if we have
+         * one. If it is a non-NULL empty strv, we'll report it as explicit empty list. When the field is
+         * NULL and we have no default list we'll return NULL. */
+
         /* Note that we intentionally distinguish between NULL and an empty array here */
-        return (const char**) h->self_modifiable_fields ?: (const char**) default_fields;
+        if (h->self_modifiable_fields)
+                return (const char**) h->self_modifiable_fields;
+
+        return user_record_disposition(h) == USER_REGULAR ? (const char**) default_fields : NULL;
 }
 
 const char** user_record_self_modifiable_blobs(UserRecord *h) {
@@ -2180,7 +2187,10 @@ const char** user_record_self_modifiable_blobs(UserRecord *h) {
         assert(h);
 
         /* Note that we intentionally distinguish between NULL and an empty array here */
-        return (const char**) h->self_modifiable_blobs ?: (const char**) default_blobs;
+        if (h->self_modifiable_blobs)
+                return (const char**) h->self_modifiable_blobs;
+
+        return user_record_disposition(h) == USER_REGULAR ? (const char**) default_blobs : NULL;
 }
 
 const char** user_record_self_modifiable_privileged(UserRecord *h) {
@@ -2201,7 +2211,10 @@ const char** user_record_self_modifiable_privileged(UserRecord *h) {
         assert(h);
 
         /* Note that we intentionally distinguish between NULL and an empty array here */
-        return (const char**) h->self_modifiable_privileged ?: (const char**) default_fields;
+        if (h->self_modifiable_privileged)
+                return (const char**) h->self_modifiable_privileged;
+
+        return user_record_disposition(h) == USER_REGULAR ? (const char**) default_fields : NULL;
 }
 
 static int remove_self_modifiable_json_fields_common(UserRecord *current, sd_json_variant **target) {

src/test/test-user-record.c

@@ -9,7 +9,7 @@
         ({                                      \
                 typeof(ret) _r = (ret);         \
                 user_record_unref(*_r);         \
-                assert_se(user_record_build((ret), SD_JSON_BUILD_OBJECT(__VA_ARGS__)) >= 0); \
+                assert_se(user_record_build((ret), SD_JSON_BUILD_OBJECT(SD_JSON_BUILD_PAIR_STRING("disposition", "regular"), __VA_ARGS__)) >= 0); \
                 0;                              \
         })