Commit 726a4994 authored Jul 15, 2016 by Eric W. Biederman Committed by Tejun Heo Jul 15, 2016

cgroupns: Only allow creation of hierarchies in the initial cgroup namespace



Unprivileged users can't use hierarchies if they create them as they do not
have privilieges to the root directory.

Which means the only thing a hiearchy created by an unprivileged user
is good for is expanding the number of cgroup links in every css_set,
which is a DOS attack.

We could allow hierarchies to be created in namespaces in the initial
user namespace.  Unfortunately there is only a single namespace for
the names of heirarchies, so that is likely to create more confusion
than not.

So do the simple thing and restrict hiearchy creation to the initial
cgroup namespace.

Cc: stable@vger.kernel.org
Fixes: a79a908f ("cgroup: introduce cgroup namespaces")
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

parent eedd0f4c

kernel/cgroup.c

+2 −6

Original line number	Diff line number	Diff line
		@@ -2215,12 +2215,8 @@ static struct dentry cgroup_mount(struct file_system_type fs_type,
		goto out_unlock;
		}

		/*
		* We know this subsystem has not yet been bound. Users in a non-init
		* user namespace may only mount hierarchies with no bound subsystems,
		* i.e. 'none,name=user1'
		*/
		if (!opts.none && !capable(CAP_SYS_ADMIN)) {
		/* Hierarchies may only be created in the initial cgroup namespace. */
		if (ns != &init_cgroup_ns) {
		ret = -EPERM;
		goto out_unlock;
		}