2 files changed, 21 insertions, 0 deletions

diff --git a/Documentation/namespaces/resource-control.txt b/Documentation/namespaces/resource-control.txt
new file mode 100644
index 000000000000..abc13c394738
--- /dev/null
+++ b/Documentation/namespaces/resource-control.txt
@@ -0,0 +1,14 @@
+There are a lot of kinds of objects in the kernel that don't have
+individual limits or that have limits that are ineffective when a set
+of processes is allowed to switch user ids.  With user namespaces
+enabled in a kernel for people who don't trust their users or their
+users programs to play nice this problems becomes more acute.
+
+Therefore it is recommended that memory control groups be enabled in
+kernels that enable user namespaces, and it is further recommended
+that userspace configure memory control groups to limit how much
+memory user's they don't trust to play nice can use.
+
+Memory control groups can be configured by installing the libcgroup
+package present on most distros editing /etc/cgrules.conf,
+/etc/cgconfig.conf and setting up libpam-cgroup.
diff --git a/init/Kconfig b/init/Kconfig
index 7d30240e5bfe..c8c58bddfed3 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1035,6 +1035,13 @@ config USER_NS
         help
           This allows containers, i.e. vservers, to use user namespaces
           to provide different user info for different servers.
+
+          When user namespaces are enabled in the kernel it is
+          recommended that the MEMCG and MEMCG_KMEM options also be
+          enabled and that user-space use the memory control groups to
+          limit the amount of memory a memory unprivileged users can
+          use.
+
           If unsure, say N.
 
 config PID_NS