cgroup: cgroup namespace setns support

setns on a cgroup namespace is allowed only if
task has CAP_SYS_ADMIN in its current user-namespace and
over the user-namespace associated with target cgroupns.
No implicit cgroup changes happen with attaching to another
cgroupns. It is expected that the somone moves the attaching
process under the target cgroupns-root.

Signed-off-by: Aditya Kali <adityakali@google.com>
Signed-off-by: Serge E. Hallyn <serge.hallyn@canonical.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index b001c5d36becf0f35cf0343eccdb82dcad16f1ab..b086a461be23a05d443085c3125366a19c0646ae 100644 (file)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -6057,10 +6057,23 @@ static inline struct cgroup_namespace *to_cg_ns(struct ns_common *ns)
        return container_of(ns, struct cgroup_namespace, ns);
 }
 
-static int cgroupns_install(struct nsproxy *nsproxy, void *ns)
+static int cgroupns_install(struct nsproxy *nsproxy, struct ns_common *ns)
 {
-       pr_info("setns not supported for cgroup namespace");
-       return -EINVAL;
+       struct cgroup_namespace *cgroup_ns = to_cg_ns(ns);
+
+       if (!ns_capable(current_user_ns(), CAP_SYS_ADMIN) ||
+           !ns_capable(cgroup_ns->user_ns, CAP_SYS_ADMIN))
+               return -EPERM;
+
+       /* Don't need to do anything if we are attaching to our own cgroupns. */
+       if (cgroup_ns == nsproxy->cgroup_ns)
+               return 0;
+
+       get_cgroup_ns(cgroup_ns);
+       put_cgroup_ns(nsproxy->cgroup_ns);
+       nsproxy->cgroup_ns = cgroup_ns;
+
+       return 0;
 }
 
 static struct ns_common *cgroupns_get(struct task_struct *task)