tree df6e44746ff643f6f70773dfb1783d9ea7b729bf
parent 80dd00a23784b384ccea049bfb3f259d3f973b9d
author Eric W. Biederman <ebiederm@xmission.com> 1417065734 -0600
committer Eric W. Biederman <ebiederm@xmission.com> 1418166512 -0600

userns: Only allow the creator of the userns unprivileged mappings

If you did not create the user namespace and are allowed
to write to uid_map or gid_map you should already have the necessary
privilege in the parent user namespace to establish any mapping
you want so this will not affect userspace in practice.

Limiting unprivileged uid mapping establishment to the creator of the
user namespace makes it easier to verify all credentials obtained with
the uid mapping can be obtained without the uid mapping without
privilege.

Limiting unprivileged gid mapping establishment (which is temporarily
absent) to the creator of the user namespace also ensures that the
combination of uid and gid can already be obtained without privilege.

This is part of the fix for CVE-2014-8989.

Cc: stable@vger.kernel.org
Reviewed-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>