In the help text describing user namespaces recommend use of memory
control groups. In many cases memory control groups are the only
mechanism there is to limit how much memory a user who can create
user namespaces can use.
Signed-off-by: "Eric W. Biederman" <ebied...@xmission.com>
---
Documentation/namespaces/resource-control.txt | 10 ++++++++++
init/Kconfig | 7 +++++++
2 files changed, 17 insertions(+), 0 deletions(-)
create mode 100644 Documentation/namespaces/resource-control.txt
diff --git a/Documentation/namespaces/resource-control.txt
b/Documentation/namespaces/resource-control.txt
new file mode 100644
index 0000000..3d8178a
--- /dev/null
+++ b/Documentation/namespaces/resource-control.txt
@@ -0,0 +1,10 @@
+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 users they don't trust to play nice can use.
diff --git a/init/Kconfig b/init/Kconfig
index 7d30240..c8c58bd 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
--
1.7.5.4
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