Date: Fri, 20 Jul 2018 08:37:04 -0500 From: ebiederm@...ssion.com (Eric W. Biederman) To: Salvatore Mesoraca <s.mesoraca16@...il.com> Cc: Kernel Hardening <kernel-hardening@...ts.openwall.com>, Laura Abbott <labbott@...hat.com>, LKML <linux-kernel@...r.kernel.org>, Masahiro Yamada <yamada.masahiro@...ionext.com>, linux-doc@...r.kernel.org, Kees Cook <keescook@...omium.org> Subject: Re: [RFC] kconfig: add hardened defconfig helpers Kees Cook <keescook@...omium.org> writes: >> +CONFIG_USER_NS=n >> +~~~~~~~~~~~~~~~~ >> + >> +**Negative side effects level:** Medium > > Unfortunately I think this is High or Extreme. USER_NS gets a lot of use. > >> +**- Protection type:** Attack surface reduction >> + >> +This allows containers to use user namespaces to provide different >> +user info for different servers. >> +User namespaces have been abused in the past for privilege >> +escalation. This is not a particularly good description. User namespaces do indeed increase the attack surface of programs that don't use them. User namespaces when used to build ``unprivileged containers'' remove or at least drastically reduce the need to run as root when setting up containers. Which is attack surface reduction. User namespaces make available tools that are commonly used to build sandboxes. Chrome for example uses users namespaces if they are available as part of setting up it's sandbox. User namespaces are not limited to containers. The bugs in the attack surface that user namespaces expose that have been used for privilege escalation have to the best of my knowledge closed. So while there is some danger in the increased attack surface we are looking at implementation defects rather than design defects. Eric
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