+static int get_invocation_from_keyring(sd_id128_t *ret) {
+
+ _cleanup_free_ char *description = NULL;
+ char *d, *p, *g, *u, *e;
+ unsigned long perms;
+ key_serial_t key;
+ size_t sz = 256;
+ uid_t uid;
+ gid_t gid;
+ int r, c;
+
+#define MAX_PERMS ((unsigned long) (KEY_POS_VIEW|KEY_POS_READ|KEY_POS_SEARCH| \
+ KEY_USR_VIEW|KEY_USR_READ|KEY_USR_SEARCH))
+
+ assert(ret);
+
+ key = request_key("user", "invocation_id", NULL, 0);
+ if (key == -1) {
+ /* Keyring support not available? No invocation key stored? */
+ if (IN_SET(errno, ENOSYS, ENOKEY))
+ return 0;
+
+ return -errno;
+ }
+
+ for (;;) {
+ description = new(char, sz);
+ if (!description)
+ return -ENOMEM;
+
+ c = keyctl(KEYCTL_DESCRIBE, key, (unsigned long) description, sz, 0);
+ if (c < 0)
+ return -errno;
+
+ if ((size_t) c <= sz)
+ break;
+
+ sz = c;
+ free(description);
+ }
+
+ /* The kernel returns a final NUL in the string, verify that. */
+ assert(description[c-1] == 0);
+
+ /* Chop off the final description string */
+ d = strrchr(description, ';');
+ if (!d)
+ return -EIO;
+ *d = 0;
+
+ /* Look for the permissions */
+ p = strrchr(description, ';');
+ if (!p)
+ return -EIO;
+
+ errno = 0;
+ perms = strtoul(p + 1, &e, 16);
+ if (errno > 0)
+ return -errno;
+ if (e == p + 1) /* Read at least one character */
+ return -EIO;
+ if (e != d) /* Must reached the end */
+ return -EIO;
+
+ if ((perms & ~MAX_PERMS) != 0)
+ return -EPERM;
+
+ *p = 0;
+
+ /* Look for the group ID */
+ g = strrchr(description, ';');
+ if (!g)
+ return -EIO;
+ r = parse_gid(g + 1, &gid);
+ if (r < 0)
+ return r;
+ if (gid != 0)
+ return -EPERM;
+ *g = 0;
+
+ /* Look for the user ID */
+ u = strrchr(description, ';');
+ if (!u)
+ return -EIO;
+ r = parse_uid(u + 1, &uid);
+ if (r < 0)
+ return r;
+ if (uid != 0)
+ return -EPERM;
+
+ c = keyctl(KEYCTL_READ, key, (unsigned long) ret, sizeof(sd_id128_t), 0);
+ if (c < 0)
+ return -errno;
+ if (c != sizeof(sd_id128_t))
+ return -EIO;
+
+ return 1;
+}
+