user-classification: add new "foreign" UID range

This makes the UID range configurable via build time options, but of
course it really shouldn't be changed. The default range I picked is
outside even of IPAs current (ridiculously large) allocation ranges,
hence hopefully minimizes conflicts.

src/basic/uid-classification.c

@@ -127,5 +127,5 @@ bool uid_for_system_journal(uid_t uid) {
 
         /* Returns true if the specified UID shall get its data stored in the system journal. */
 
-        return uid_is_system(uid) || uid_is_dynamic(uid) || uid == UID_NOBODY || uid_is_container(uid);
+        return uid_is_system(uid) || uid_is_dynamic(uid) || uid == UID_NOBODY || uid_is_container(uid) || uid_is_foreign(uid);
 }

src/basic/uid-classification.h

@@ -12,6 +12,10 @@ assert_cc((CONTAINER_UID_BASE_MAX & 0xFFFFU) == 0);
 #define CONTAINER_UID_MIN (CONTAINER_UID_BASE_MIN)
 #define CONTAINER_UID_MAX (CONTAINER_UID_BASE_MAX + 0xFFFFU)
 
+assert_cc((FOREIGN_UID_BASE & 0xFFFFU) == 0);
+#define FOREIGN_UID_MIN (FOREIGN_UID_BASE)
+#define FOREIGN_UID_MAX (FOREIGN_UID_BASE + 0xFFFFU)
+
 bool uid_is_system(uid_t uid);
 bool gid_is_system(gid_t gid);
 
@@ -31,6 +35,14 @@ static inline bool gid_is_container(gid_t gid) {
         return uid_is_container((uid_t) gid);
 }
 
+static inline bool uid_is_foreign(uid_t uid) {
+        return FOREIGN_UID_MIN <= uid && uid <= FOREIGN_UID_MAX;
+}
+
+static inline bool gid_is_foreign(gid_t gid) {
+        return uid_is_foreign((uid_t) gid);
+}
+
 typedef struct UGIDAllocationRange {
         uid_t system_alloc_uid_min;
         uid_t system_uid_max;