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

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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: a79a908fd2 ("cgroup: introduce cgroup namespaces")
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Eric W. Biederman 2016-07-15 06:36:44 -05:00 committed by Tejun Heo
parent eedd0f4cbf
commit 726a4994b0
1 changed files with 2 additions and 6 deletions
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8
kernel/cgroup.c
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@ -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;
}