Date: Mon, 6 Nov 2017 23:42:08 +0100 From: Christian Brauner <christian.brauner@...onical.com> To: "Serge E. Hallyn" <serge@...lyn.com> Cc: Daniel Micay <danielmicay@...il.com>, Mahesh Bandewar (महेश बंडेवार) <maheshb@...gle.com>, Mahesh Bandewar <mahesh@...dewar.net>, LKML <linux-kernel@...r.kernel.org>, Netdev <netdev@...r.kernel.org>, Kernel-hardening <kernel-hardening@...ts.openwall.com>, Linux API <linux-api@...r.kernel.org>, Kees Cook <keescook@...omium.org>, "Eric W . Biederman" <ebiederm@...ssion.com>, Eric Dumazet <edumazet@...gle.com>, David Miller <davem@...emloft.net> Subject: Re: Re: [PATCH resend 2/2] userns: control capabilities of some user namespaces On Mon, Nov 06, 2017 at 04:14:18PM -0600, Serge Hallyn wrote: > Quoting Daniel Micay (danielmicay@...il.com): > > Substantial added attack surface will never go away as a problem. There > > aren't a finite number of vulnerabilities to be found. > > There's varying levels of usefulness and quality. There is code which I > want to be able to use in a container, and code which I can't ever see a > reason for using there. The latter, especially if it's also in a > staging driver, would be nice to have a toggle to disable. > > You're not advocating dropping the added attack surface, only adding a > way of dealing with an 0day after the fact. Privilege raising 0days can > exist anywhere, not just in code which only root in a user namespace can > exercise. So from that point of view, ksplice seems a more complete > solution. Why not just actually fix the bad code block when we know > about it? > > Finally, it has been well argued that you can gain many new caps from > having only a few others. Given that, how could you ever be sure that, > if an 0day is found which allows root in a user ns to abuse > CAP_NET_ADMIN against the host, just keeping CAP_NET_ADMIN from them > would suffice? It seems to me that the existing control in > /proc/sys/kernel/unprivileged_userns_clone might be the better duct tape > in that case. I agree that /proc/sys/kernel/unprivileged_userns_clone is the most reasonable thing to do. This patch introduces a layer of complexity to fine-tune user namespace creation that - in the relevant security critical scenario - should simply be turned of entirely. Is /proc/sys/kernel/unprivileged_userns_clone upstreamed or is this still only carried downstream?
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