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userns: Recommend use of memory control groups.

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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.

Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
This commit is contained in:
Eric W. Biederman 2013-01-25 16:48:31 -08:00
parent 0bd14b4fd7
commit e11f0ae388
2 changed files with 21 additions and 0 deletions
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14
Documentation/namespaces/resource-control.txt Normal file
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@ -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.

7
init/Kconfig
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@ -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