nemunai.re/content/en/post/user-ns-for-grsecurity/index.md

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Support for the user namespace in grsecurity kernel 2018-10-31 00:00:00
kernel

Grsecurity has completely disabled, on purpose, the user namespace code for the kernel.

As the goal of this namespace is to gain (virtualy) root privilegies inside a namespace (in theory, it shouldn't give more priviledgies than the one you initialy have outside of your namespace), there are some interesting use cases, or, in my case I need to perform some demo in front of my students.

Other distros, like Debian, choose to allow the use of user namespace through a custom kernel config variable. In order to use them without both CAP_SYS_ADMIN, CAP_SETUID and CAP_SETGID, you need to activate (as root):

42sh# sysctl -w kernel.unprivileged_userns_clone=1

To reproduce the same behaviour with a grsecurity kernel, I made a patch, to apply after the grsecurity patch: grsec-enable-user-ns.patch.