multiuser: Change all groups in setup_environment.

We need to change all groups, not just the primary group.
Otherwise, other groups will be left intact, which may
include groups the new user doesn't have permissions for.

src/bin/multiuser/multiuser_utils.cpp

@@ -202,6 +202,9 @@ setup_environment(struct passwd* passwd, bool preserveEnvironment, bool chngdir)
 	if (passwd->pw_gid && setgid(passwd->pw_gid) != 0)
 		return errno;
 
+	if (initgroups(passwd->pw_name, passwd->pw_gid) != 0)
+		return errno;
+
 	if (passwd->pw_uid && setuid(passwd->pw_uid) != 0)
 		return errno;