Re: [PATCH v2 02/10] userns: Add per user namespace sysctls.

From: ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org (Eric W. Biederman)
Date: Mon, 25 Jul 2016 19:44:50 -0500

User namespaces have enabled unprivileged users access to a lot more
data structures and so to catch programs that go crazy we need a lot
more limits.  I believe some of those limits make sense per namespace.
As it is easy in some cases to say any more than Y number of those
per namespace is excessive.   For example a limit of 1,000,000 ipv4
routes per network namespaces is a sanity check as there are
currently 621,649 ipv4 prefixes advertized in bgp.

When we give a new namespace to unprivileged users, we honestly should
make the sysctl settings we give to them become "limits".  They can
further constrain the sysctl settings but may not raise them.