[PATCHv3 6/8] cgroup: cgroup namespace setns support

[Aditya Kali]

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 at google.com>
---
 kernel/cgroup_namespace.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/kernel/cgroup_namespace.c b/kernel/cgroup_namespace.c
index 0e0ef3a..ee0cc51 100644
--- a/kernel/cgroup_namespace.c
+++ b/kernel/cgroup_namespace.c
@@ -79,8 +79,21 @@ err_out:
 
 static int cgroupns_install(struct nsproxy *nsproxy, void *ns)
 {
-	pr_info("setns not supported for cgroup namespace");
-	return -EINVAL;
+	struct cgroup_namespace *cgroup_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 void *cgroupns_get(struct task_struct *task)
-- 
2.2.0.rc0.207.ga3a616c