linux-kernel - [PATCH 4/8] cgroup: cgroup namespace setns support

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Message-Id: <1454057651-23959-5-git-send-email-serge.hallyn@ubuntu.com>
Date:	Fri, 29 Jan 2016 02:54:07 -0600
From:	serge.hallyn@...ntu.com
To:	linux-kernel@...r.kernel.org
Cc:	adityakali@...gle.com, tj@...nel.org, linux-api@...r.kernel.org,
	containers@...ts.linux-foundation.org, cgroups@...r.kernel.org,
	lxc-devel@...ts.linuxcontainers.org, akpm@...ux-foundation.org,
	ebiederm@...ssion.com, gregkh@...uxfoundation.org,
	lizefan@...wei.com, hannes@...xchg.org,
	"Serge E. Hallyn" <serge.hallyn@...onical.com>
Subject: [PATCH 4/8] cgroup: cgroup namespace setns support

From: Aditya Kali <adityakali@...gle.com>

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@...gle.com>
Signed-off-by: Serge E. Hallyn <serge.hallyn@...onical.com>
---
 kernel/cgroup.c |   19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index d828e1f..96e3dab 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -6004,10 +6004,23 @@ 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)
-- 
1.7.9.5