1 files changed, 124 insertions, 0 deletions
diff --git a/src/shared/uid-alloc-range.c b/src/shared/uid-alloc-range.c
new file mode 100644
index 0000000..1953119
--- /dev/null
+++ b/src/shared/uid-alloc-range.c
@@ -0,0 +1,124 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include "chase-symlinks.h"
+#include "fd-util.h"
+#include "fileio.h"
+#include "missing_threads.h"
+#include "string-util.h"
+#include "uid-alloc-range.h"
+#include "user-util.h"
+
+static const UGIDAllocationRange default_ugid_allocation_range = {
+        .system_alloc_uid_min = SYSTEM_ALLOC_UID_MIN,
+        .system_uid_max = SYSTEM_UID_MAX,
+        .system_alloc_gid_min = SYSTEM_ALLOC_GID_MIN,
+        .system_gid_max = SYSTEM_GID_MAX,
+};
+
+#if ENABLE_COMPAT_MUTABLE_UID_BOUNDARIES
+static int parse_alloc_uid(const char *path, const char *name, const char *t, uid_t *ret_uid) {
+        uid_t uid;
+        int r;
+
+        r = parse_uid(t, &uid);
+        if (r < 0)
+                return log_debug_errno(r, "%s: failed to parse %s %s, ignoring: %m", path, name, t);
+        if (uid == 0)
+                uid = 1;
+
+        *ret_uid = uid;
+        return 0;
+}
+#endif
+
+int read_login_defs(UGIDAllocationRange *ret_defs, const char *path, const char *root) {
+#if ENABLE_COMPAT_MUTABLE_UID_BOUNDARIES
+        _cleanup_fclose_ FILE *f = NULL;
+        UGIDAllocationRange defs;
+        int r;
+
+        if (!path)
+                path = "/etc/login.defs";
+
+        r = chase_symlinks_and_fopen_unlocked(path, root, CHASE_PREFIX_ROOT, "re", NULL, &f);
+        if (r == -ENOENT)
+                goto defaults;
+        if (r < 0)
+                return log_debug_errno(r, "Failed to open %s: %m", path);
+
+        defs = default_ugid_allocation_range;
+
+        for (;;) {
+                _cleanup_free_ char *line = NULL;
+                char *t;
+
+                r = read_line(f, LINE_MAX, &line);
+                if (r < 0)
+                        return log_debug_errno(r, "Failed to read %s: %m", path);
+                if (r == 0)
+                        break;
+
+                if ((t = first_word(line, "SYS_UID_MIN")))
+                        (void) parse_alloc_uid(path, "SYS_UID_MIN", t, &defs.system_alloc_uid_min);
+                else if ((t = first_word(line, "SYS_UID_MAX")))
+                        (void) parse_alloc_uid(path, "SYS_UID_MAX", t, &defs.system_uid_max);
+                else if ((t = first_word(line, "SYS_GID_MIN")))
+                        (void) parse_alloc_uid(path, "SYS_GID_MIN", t, &defs.system_alloc_gid_min);
+                else if ((t = first_word(line, "SYS_GID_MAX")))
+                        (void) parse_alloc_uid(path, "SYS_GID_MAX", t, &defs.system_gid_max);
+        }
+
+        if (defs.system_alloc_uid_min > defs.system_uid_max) {
+                log_debug("%s: SYS_UID_MIN > SYS_UID_MAX, resetting.", path);
+                defs.system_alloc_uid_min = MIN(defs.system_uid_max - 1, (uid_t) SYSTEM_ALLOC_UID_MIN);
+                /* Look at sys_uid_max to make sure sys_uid_min..sys_uid_max remains a valid range. */
+        }
+        if (defs.system_alloc_gid_min > defs.system_gid_max) {
+                log_debug("%s: SYS_GID_MIN > SYS_GID_MAX, resetting.", path);
+                defs.system_alloc_gid_min = MIN(defs.system_gid_max - 1, (gid_t) SYSTEM_ALLOC_GID_MIN);
+                /* Look at sys_gid_max to make sure sys_gid_min..sys_gid_max remains a valid range. */
+        }
+
+        *ret_defs = defs;
+        return 1;
+defaults:
+#endif
+        *ret_defs = default_ugid_allocation_range;
+        return 0;
+}
+
+const UGIDAllocationRange *acquire_ugid_allocation_range(void) {
+#if ENABLE_COMPAT_MUTABLE_UID_BOUNDARIES
+        static thread_local UGIDAllocationRange defs;
+        static thread_local int initialized = 0; /* == 0 → not initialized yet
+                                                  * < 0 → failure
+                                                  * > 0 → success */
+
+        /* This function will ignore failure to read the file, so it should only be called from places where
+         * we don't crucially depend on the answer. In other words, it's appropriate for journald, but
+         * probably not for sysusers. */
+
+        if (initialized == 0)
+                initialized = read_login_defs(&defs, NULL, NULL) < 0 ? -1 : 1;
+        if (initialized < 0)
+                return &default_ugid_allocation_range;
+
+        return &defs;
+
+#endif
+        return &default_ugid_allocation_range;
+}
+
+bool uid_is_system(uid_t uid) {
+        const UGIDAllocationRange *defs;
+        assert_se(defs = acquire_ugid_allocation_range());
+
+        return uid <= defs->system_uid_max;
+}
+
+bool gid_is_system(gid_t gid) {
+        const UGIDAllocationRange *defs;
+        assert_se(defs = acquire_ugid_allocation_range());
+
+        return gid <= defs->system_gid_max;
+}