CGroup Namespaces (v8)

@@ -5925,10 +5925,28 @@ err_out:
 	return ERR_PTR(err);
 }
 
-static int cgroupns_install(struct nsproxy *nsproxy, void *ns)
+static inline struct cgroup_namespace *to_cg_ns(struct ns_common *ns)
 {
-	pr_info("setns not supported for cgroup namespace");
-	return -EINVAL;
+	return container_of(ns, struct cgroup_namespace, ns);
+}
+
+static int cgroupns_install(struct nsproxy *nsproxy, struct ns_common *ns)
+{
+	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)

@@ -21,8 +21,7 @@
 #define CLONE_DETACHED		0x00400000	/* Unused, ignored */
 #define CLONE_UNTRACED		0x00800000	/* set if the tracing process can't force CLONE_PTRACE on this clone */
 #define CLONE_CHILD_SETTID	0x01000000	/* set the TID in the child */
-/* 0x02000000 was previously the unused CLONE_STOPPED (Start in stopped state)
-   and is now available for re-use. */
+#define CLONE_NEWCGROUP		0x02000000	/* New cgroup namespace */
 #define CLONE_NEWUTS		0x04000000	/* New utsname namespace */
 #define CLONE_NEWIPC		0x08000000	/* New ipc namespace */
 #define CLONE_NEWUSER		0x10000000	/* New user namespace */

@@ -47,6 +47,7 @@ CONTENTS
   5-3. IO
     5-3-1. IO Interface Files
     5-3-2. Writeback
+6. Namespaces
 P. Information on Kernel Programming
   P-1. Filesystem Support for Writeback
 D. Deprecated v1 Core Features

@@ -1013,6 +1014,155 @@ writeback as follows.
 	vm.dirty[_background]_ratio.
 
 
+6. Cgroup Namespaces
+
+Cgroup namespaces provides a mechanism to virtualize the view of the
+"/proc/$PID/cgroup" file. The CLONE_NEWCGROUP clone flag can be used with
+clone() and unshare() syscalls to create a new cgroup namespace.  The process
+running inside the cgroup namespace will have its "/proc/$PID/cgroup" output
+restricted to cgroupns root.  The cgroupns root is the cgroup of the process at
+the time of creation of the cgroup namespace.
+
+Prior to cgroup namespaces, the "/proc/$PID/cgroup" file showed the complete
+path of the cgroup of a process. In a container setup where a set of cgroups
+and namespaces are intended to isolate processes the "/proc/$PID/cgroup" file
+may leak potential system level information to the isolated processes.
+
+For Example:
+  # cat /proc/self/cgroup
+  0:cpuset,cpu,cpuacct,memory,devices,freezer,hugetlb:/batchjobs/container_id1
+
+The path '/batchjobs/container_id1' can generally be considered as system-data
+and its desirable to not expose it to the isolated process.
+
+Cgroup namespaces can be used to restrict visibility of this path.
+For example, before creating a cgroup namespace, one would see:
+
+  # ls -l /proc/self/ns/cgroup
+  lrwxrwxrwx 1 root root 0 2014-07-15 10:37 /proc/self/ns/cgroup -> cgroup:[4026531835]
+  # cat /proc/self/cgroup
+  0:cpuset,cpu,cpuacct,memory,devices,freezer,hugetlb:/batchjobs/container_id1
+
+After unsharing a new namespace, the view has changed.
+
+  # ls -l /proc/self/ns/cgroup
+  lrwxrwxrwx 1 root root 0 2014-07-15 10:35 /proc/self/ns/cgroup -> cgroup:[4026532183]
+  # cat /proc/self/cgroup
+  0:cpuset,cpu,cpuacct,memory,devices,freezer,hugetlb:/
+
+While a task in the global cgroup namespace sees the full path.
+
+  # cat /proc/$PID/cgroup
+  0:cpuset,cpu,cpuacct,memory,devices,freezer,hugetlb:/batchjobs/container_id1
+
+If also unsharing the user and mounts namespaces, then when mounting cgroupfs
+then the mount's root will be the task's cgroup.
+
+  # lxc-usernsexec --unshare -m -c
+  # mount -t cgroup cgroup /tmp/cgroup
+  # ls -l /tmp/cgroup
+  total 0
+  -r--r--r-- 1 root root 0 2014-10-13 09:32 cgroup.controllers
+  -r--r--r-- 1 root root 0 2014-10-13 09:32 cgroup.populated
+  -rw-r--r-- 1 root root 0 2014-10-13 09:25 cgroup.procs
+  -rw-r--r-- 1 root root 0 2014-10-13 09:32 cgroup.subtree_control
+
+The cgroupns root (/batchjobs/container_id1 in above example) becomes the
+filesystem root for the namespace specific cgroupfs mount.
+
+The virtualization of /proc/self/cgroup file combined with restricting
+the view of cgroup hierarchy by namespace-private cgroupfs mount
+should provide a completely isolated cgroup view inside the container.
+
+In its current form, the cgroup namespaces patcheset provides following
+behavior:
+
+(1) The 'cgroupns root' for a cgroup namespace is the cgroup in which
+    the process calling unshare is running.
+    For ex. if a process in /batchjobs/container_id1 cgroup calls unshare,
+    cgroup /batchjobs/container_id1 becomes the cgroupns root.
+    For the init_cgroup_ns, this is the real root ('/') cgroup
+    (identified in code as cgrp_dfl_root.cgrp).
+
+(2) The cgroupns root cgroup does not change even if the namespace
+    creator process later moves to a different cgroup.
+    # ~/unshare -c # unshare cgroupns in some cgroup
+     # cat /proc/self/cgroup
+     0:cpuset,cpu,cpuacct,memory,devices,freezer,hugetlb:/
+     # mkdir sub_cgrp_1
+     # echo 0 > sub_cgrp_1/cgroup.procs
+     # cat /proc/self/cgroup
+     0:cpuset,cpu,cpuacct,memory,devices,freezer,hugetlb:/sub_cgrp_1
+
+(3) Each process gets its namespace-specific view of "/proc/$PID/cgroup"
+
+(a) Processes running inside the cgroup namespace will be able to see
+    cgroup paths (in /proc/self/cgroup) only inside their root cgroup.
+    From within an unshared cgroupns:
+    # sleep 100000 &
+    [1] 7353
+    # echo 7353 > sub_cgrp_1/cgroup.procs
+    # cat /proc/7353/cgroup
+    0:cpuset,cpu,cpuacct,memory,devices,freezer,hugetlb:/sub_cgrp_1
+
+(b) From the initial cgroup namespace, the real cgroup path will be visible:
+    $ cat /proc/7353/cgroup
+    0:cpuset,cpu,cpuacct,memory,devices,freezer,hugetlb:/batchjobs/container_id1/sub_cgrp_1
+
+(c) From a sibling cgroup namespace (that is, a namespace rooted at a
+    different cgroup), the cgroup path relative to its own cgroup namespace
+    root will be shown.  For instance, if PID 7353's cgroup namespace root is
+    at '/batchjobs/container_id2', then it will see
+
+    # cat /proc/7353/cgroup
+    0:cpuset,cpu,cpuacct,memory,devices,freezer,hugetlb:/../container_id2/sub_cgrp_1
+
+    Note that the relative path always starts with '/' to indicate that its
+    relative to the cgroup namespace root of the caller.
+
+(4) Processes inside a cgroup namespace can move into and out of the namespace
+    root if they have proper access to external cgroups.  So from inside a
+    namespace with cgroupns root at /batchjobs/container_id1, and
+    assuming that the global hierarchy is still accessible inside cgroupns:
+
+    # cat /proc/7353/cgroup
+    0:cpuset,cpu,cpuacct,memory,devices,freezer,hugetlb:/sub_cgrp_1
+    # echo 7353 > batchjobs/container_id2/cgroup.procs
+    # cat /proc/7353/cgroup
+    0:cpuset,cpu,cpuacct,memory,devices,freezer,hugetlb:/../container_id2
+
+    Note that this kind of setup is not encouraged. A task inside cgroup
+    namespace should only be exposed to its own cgroupns hierarchy. Otherwise
+    it makes the virtualization of "/proc/$PID/cgroup" less useful.
+
+(5) Setns to another cgroup namespace is allowed when:
+    (a) the process has CAP_SYS_ADMIN against its current user namespace
+    (b) the process has CAP_SYS_ADMIN against the target cgroup namespace's
+        userns
+    No implicit cgroup changes happen with attaching to another cgroup
+    namespace. It is expected that the somone moves the attaching process under
+    the target cgroup namespace root.
+
+(6) When some thread from a multi-threaded process unshares its
+    cgroup namespace, the new cgroupns gets applied to the entire process (all
+    the threads). For the unified hierarchy this is expected as it only allows
+    process level containerization.  For the legacy hierarchies this may be
+    unexpected.  So all the threads in the process will have the same cgroup.
+
+(7) The cgroup namespace is alive as long as there is at least 1
+    process inside it.  When the last process exits, the cgroup
+    namespace is destroyed. The cgroupns root and the actual cgroups
+    remain.
+
+(8) Namespace specific cgroup hierarchy can be mounted by a process running
+    inside a non-init cgroup namespace:
+
+    # mount -t cgroup -o __DEVEL__sane_behavior cgroup $MOUNT_POINT
+
+    This will mount the unified cgroup hierarchy with cgroupns root as the
+    filesystem root. The process needs CAP_SYS_ADMIN against its user and
+    mounts namespaces.
+
 P. Information on Kernel Programming
 
 This section contains kernel programming information in the areas

@@ -2208,12 +2208,14 @@ static struct file_system_type cgroup_fs_type = {
 	.name = "cgroup",
 	.mount = cgroup_mount,
 	.kill_sb = cgroup_kill_sb,
+	.fs_flags = FS_USERNS_MOUNT,
 };
 
 static struct file_system_type cgroup2_fs_type = {
 	.name = "cgroup2",
 	.mount = cgroup_mount,
 	.kill_sb = cgroup_kill_sb,
+	.fs_flags = FS_USERNS_MOUNT,
 };
 
 static int cgroup_path_ns(struct cgroup *cgrp, char *buf, size_t buflen,

@@ -1983,6 +1983,7 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type,
 {
 	bool is_v2 = fs_type == &cgroup2_fs_type;
 	struct super_block *pinned_sb = NULL;
+	struct cgroup_namespace *ns = current->nsproxy->cgroup_ns;
 	struct cgroup_subsys *ss;
 	struct cgroup_root *root;
 	struct cgroup_sb_opts opts;

@@ -1991,6 +1992,14 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type,
 	int i;
 	bool new_sb;
 
+	get_cgroup_ns(ns);
+
+	/* Check if the caller has permission to mount. */
+	if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN)) {
+		put_cgroup_ns(ns);
+		return ERR_PTR(-EPERM);
+	}
+
 	/*
 	 * The first time anyone tries to mount a cgroup, enable the list
 	 * linking each css_set to its tasks and fix up all existing tasks.

@@ -2106,6 +2115,16 @@ 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)) {
+		ret = -EPERM;
+		goto out_unlock;
+	}
+
 	root = kzalloc(sizeof(*root), GFP_KERNEL);
 	if (!root) {
 		ret = -ENOMEM;

@@ -2124,12 +2143,30 @@ out_free:
 	kfree(opts.release_agent);
 	kfree(opts.name);
 
-	if (ret)
+	if (ret) {
+		put_cgroup_ns(ns);
 		return ERR_PTR(ret);
+	}
 out_mount:
 	dentry = kernfs_mount(fs_type, flags, root->kf_root,
 			      is_v2 ? CGROUP2_SUPER_MAGIC : CGROUP_SUPER_MAGIC,
 			      &new_sb);
+
+	/*
+	 * In non-init cgroup namespace, instead of root cgroup's
+	 * dentry, we return the dentry corresponding to the
+	 * cgroupns->root_cgrp.
+	 */
+	if (!IS_ERR(dentry) && ns != &init_cgroup_ns) {
+		struct dentry *nsdentry;
+		struct cgroup *cgrp;
+
+		cgrp = cset_cgroup_from_root(ns->root_cset, root);
+		nsdentry = kernfs_node_dentry(cgrp->kn, dentry->d_sb);
+		dput(dentry);
+		dentry = nsdentry;
+	}
+
 	if (IS_ERR(dentry) || !new_sb)
 		cgroup_put(&root->cgrp);
 

@@ -2142,6 +2179,7 @@ out_mount:
 		deactivate_super(pinned_sb);
 	}
 
+	put_cgroup_ns(ns);
 	return dentry;
 }
 

@@ -14,6 +14,7 @@
 #include <linux/magic.h>
 #include <linux/slab.h>
 #include <linux/pagemap.h>
+#include <linux/namei.h>
 
 #include "kernfs-internal.h"
 

@@ -62,6 +63,72 @@ struct kernfs_root *kernfs_root_from_sb(struct super_block *sb)
 	return NULL;
 }
 
+/*
+ * find the next ancestor in the path down to @child, where @parent was the
+ * ancestor whose descendant we want to find.
+ *
+ * Say the path is /a/b/c/d.  @child is d, @parent is NULL.  We return the root
+ * node.  If @parent is b, then we return the node for c.
+ * Passing in d as @parent is not ok.
+ */
+static struct kernfs_node *
+find_next_ancestor(struct kernfs_node *child, struct kernfs_node *parent)
+{
+	if (child == parent) {
+		pr_crit_once("BUG in find_next_ancestor: called with parent == child");
+		return NULL;
+	}
+
+	while (child->parent != parent) {
+		if (!child->parent)
+			return NULL;
+		child = child->parent;
+	}
+
+	return child;
+}
+
+/**
+ * kernfs_node_dentry - get a dentry for the given kernfs_node
+ * @kn: kernfs_node for which a dentry is needed
+ * @sb: the kernfs super_block
+ */
+struct dentry *kernfs_node_dentry(struct kernfs_node *kn,
+				  struct super_block *sb)
+{
+	struct dentry *dentry;
+	struct kernfs_node *knparent = NULL;
+
+	BUG_ON(sb->s_op != &kernfs_sops);
+
+	dentry = dget(sb->s_root);
+
+	/* Check if this is the root kernfs_node */
+	if (!kn->parent)
+		return dentry;
+
+	knparent = find_next_ancestor(kn, NULL);
+	if (WARN_ON(!knparent))
+		return ERR_PTR(-EINVAL);
+
+	do {
+		struct dentry *dtmp;
+		struct kernfs_node *kntmp;
+
+		if (kn == knparent)
+			return dentry;
+		kntmp = find_next_ancestor(kn, knparent);
+		if (WARN_ON(!kntmp))
+			return ERR_PTR(-EINVAL);
+		dtmp = lookup_one_len(kntmp->name, dentry, strlen(kntmp->name));
+		dput(dentry);
+		if (IS_ERR(dtmp))
+			return dtmp;
+		knparent = kntmp;
+		dentry = dtmp;
+	} while (1);
+}
+
 static int kernfs_fill_super(struct super_block *sb, unsigned long magic)
 {
 	struct kernfs_super_info *info = kernfs_info(sb);

@@ -284,6 +284,8 @@ struct kernfs_node *kernfs_node_from_dentry(struct dentry *dentry);
 struct kernfs_root *kernfs_root_from_sb(struct super_block *sb);
 struct inode *kernfs_get_inode(struct super_block *sb, struct kernfs_node *kn);
 
+struct dentry *kernfs_node_dentry(struct kernfs_node *kn,
+				  struct super_block *sb);
 struct kernfs_root *kernfs_create_root(struct kernfs_syscall_ops *scops,
 				       unsigned int flags, void *priv);
 void kernfs_destroy_root(struct kernfs_root *root);

@@ -28,6 +28,9 @@ static const struct proc_ns_operations *ns_entries[] = {
 	&userns_operations,
 #endif
 	&mntns_operations,
+#ifdef CONFIG_CGROUPS
+	&cgroupns_operations,
+#endif
 };
 
 static const char *proc_ns_follow_link(struct dentry *dentry, void **cookie)

@@ -17,6 +17,11 @@
 #include <linux/seq_file.h>
 #include <linux/kernfs.h>
 #include <linux/jump_label.h>
+#include <linux/nsproxy.h>
+#include <linux/types.h>
+#include <linux/ns_common.h>
+#include <linux/nsproxy.h>
+#include <linux/user_namespace.h>
 
 #include <linux/cgroup-defs.h>
 

@@ -532,12 +537,6 @@ static inline int cgroup_name(struct cgroup *cgrp, char *buf, size_t buflen)
 	return kernfs_name(cgrp->kn, buf, buflen);
 }
 
-static inline char * __must_check cgroup_path(struct cgroup *cgrp, char *buf,
-					      size_t buflen)
-{
-	return kernfs_path(cgrp->kn, buf, buflen);
-}
-
 static inline void pr_cont_cgroup_name(struct cgroup *cgrp)
 {
 	pr_cont_kernfs_name(cgrp->kn);

@@ -570,4 +569,47 @@ static inline int cgroup_init(void) { return 0; }
 
 #endif /* !CONFIG_CGROUPS */
 
+struct cgroup_namespace {
+	atomic_t		count;
+	struct ns_common	ns;
+	struct user_namespace	*user_ns;
+	struct css_set          *root_cset;
+};
+
+extern struct cgroup_namespace init_cgroup_ns;
+
+#ifdef CONFIG_CGROUPS
+
+void free_cgroup_ns(struct cgroup_namespace *ns);
+
+struct cgroup_namespace *
+copy_cgroup_ns(unsigned long flags, struct user_namespace *user_ns,
+	       struct cgroup_namespace *old_ns);
+
+char *cgroup_path(struct cgroup *cgrp, char *buf, size_t buflen);
+
+#else /* !CONFIG_CGROUPS */
+
+static inline void free_cgroup_ns(struct cgroup_namespace *ns) { }
+static inline struct cgroup_namespace *
+copy_cgroup_ns(unsigned long flags, struct user_namespace *user_ns,
+	       struct cgroup_namespace *old_ns)
+{
+	return old_ns;
+}
+
+#endif /* !CONFIG_CGROUPS */
+
+static inline void get_cgroup_ns(struct cgroup_namespace *ns)
+{
+	if (ns)
+		atomic_inc(&ns->count);
+}
+
+static inline void put_cgroup_ns(struct cgroup_namespace *ns)
+{
+	if (ns && atomic_dec_and_test(&ns->count))
+		free_cgroup_ns(ns);
+}
+
 #endif /* _LINUX_CGROUP_H */

@@ -8,6 +8,7 @@ struct mnt_namespace;
 struct uts_namespace;
 struct ipc_namespace;
 struct pid_namespace;
+struct cgroup_namespace;
 struct fs_struct;
 
 /*

@@ -33,6 +34,7 @@ struct nsproxy {
 	struct mnt_namespace *mnt_ns;
 	struct pid_namespace *pid_ns_for_children;
 	struct net 	     *net_ns;
+	struct cgroup_namespace *cgroup_ns;
 };
 extern struct nsproxy init_nsproxy;
 

@@ -9,6 +9,8 @@
 struct pid_namespace;
 struct nsproxy;
 struct path;
+struct task_struct;
+struct inode;
 
 struct proc_ns_operations {
 	const char *name;

@@ -24,6 +26,7 @@ extern const struct proc_ns_operations ipcns_operations;
 extern const struct proc_ns_operations pidns_operations;
 extern const struct proc_ns_operations userns_operations;
 extern const struct proc_ns_operations mntns_operations;
+extern const struct proc_ns_operations cgroupns_operations;
 
 /*
  * We always define these enumerators

@@ -34,6 +37,7 @@ enum {
 	PROC_UTS_INIT_INO	= 0xEFFFFFFEU,
 	PROC_USER_INIT_INO	= 0xEFFFFFFDU,
 	PROC_PID_INIT_INO	= 0xEFFFFFFCU,
+	PROC_CGROUP_INIT_INO	= 0xEFFFFFFBU,
 };
 
 #ifdef CONFIG_PROC_FS

@@ -57,6 +57,9 @@
 #include <linux/vmalloc.h> /* TODO: replace with more sophisticated array */
 #include <linux/kthread.h>
 #include <linux/delay.h>
+#include <linux/proc_ns.h>
+#include <linux/nsproxy.h>
+#include <linux/proc_ns.h>
 
 #include <linux/atomic.h>
 

@@ -208,6 +211,15 @@ static unsigned long have_fork_callback __read_mostly;
 static unsigned long have_exit_callback __read_mostly;
 static unsigned long have_free_callback __read_mostly;
 
+/* Cgroup namespace for init task */
+struct cgroup_namespace init_cgroup_ns = {
+	.count		= { .counter = 1, },
+	.user_ns	= &init_user_ns,
+	.ns.ops		= &cgroupns_operations,
+	.ns.inum	= PROC_CGROUP_INIT_INO,
+	.root_cset	= &init_css_set,
+};
+
 /* Ditto for the can_fork callback. */
 static unsigned long have_canfork_callback __read_mostly;
 

@@ -2166,6 +2178,26 @@ static struct file_system_type cgroup2_fs_type = {
 	.kill_sb = cgroup_kill_sb,
 };
 
+static int cgroup_path_ns(struct cgroup *cgrp, char *buf, size_t buflen,
+			  struct cgroup_namespace *ns)
+{
+	struct cgroup *root;
+
+	root = cset_cgroup_from_root(ns->root_cset, cgrp->root);
+	return kernfs_path_from_node(cgrp->kn, root->kn, buf, buflen);
+}
+
+char *cgroup_path(struct cgroup *cgrp, char *buf, size_t buflen)
+{
+	int ret;
+	
+	ret = cgroup_path_ns(cgrp, buf, buflen, current->nsproxy->cgroup_ns);
+	if (ret < 0 || ret >= buflen)
+		return NULL;
+	return buf;
+}
+EXPORT_SYMBOL_GPL(cgroup_path);
+
 /**
  * task_cgroup_path - cgroup path of a task in the first cgroup hierarchy
  * @task: target task

@@ -5272,6 +5304,8 @@ int __init cgroup_init(void)
 	BUG_ON(cgroup_init_cftypes(NULL, cgroup_dfl_base_files));
 	BUG_ON(cgroup_init_cftypes(NULL, cgroup_legacy_base_files));
 
+	get_user_ns(init_cgroup_ns.user_ns);
+
 	mutex_lock(&cgroup_mutex);
 
 	/* Add init_css_set to the hash table */

@@ -5822,6 +5856,116 @@ struct cgroup *cgroup_get_from_path(const char *path)
 }
 EXPORT_SYMBOL_GPL(cgroup_get_from_path);
 
+/* cgroup namespaces */
+
+static struct cgroup_namespace *alloc_cgroup_ns(void)
+{
+	struct cgroup_namespace *new_ns;
+	int ret;
+
+	new_ns = kzalloc(sizeof(struct cgroup_namespace), GFP_KERNEL);
+	if (!new_ns)
+		return ERR_PTR(-ENOMEM);
+	ret = ns_alloc_inum(&new_ns->ns);
+	if (ret) {
+		kfree(new_ns);
+		return ERR_PTR(ret);
+	}
+	atomic_set(&new_ns->count, 1);
+	new_ns->ns.ops = &cgroupns_operations;
+	return new_ns;
+}
+
+void free_cgroup_ns(struct cgroup_namespace *ns)
+{
+	put_css_set(ns->root_cset);
+	put_user_ns(ns->user_ns);
+	ns_free_inum(&ns->ns);
+	kfree(ns);
+}
+EXPORT_SYMBOL(free_cgroup_ns);
+
+struct cgroup_namespace *
+copy_cgroup_ns(unsigned long flags, struct user_namespace *user_ns,
+	       struct cgroup_namespace *old_ns)
+{
+	struct cgroup_namespace *new_ns = NULL;
+	struct css_set *cset = NULL;
+	int err;
+
+	BUG_ON(!old_ns);
+
+	if (!(flags & CLONE_NEWCGROUP)) {
+		get_cgroup_ns(old_ns);
+		return old_ns;
+	}
+
+	/* Allow only sysadmin to create cgroup namespace. */
+	err = -EPERM;
+	if (!ns_capable(user_ns, CAP_SYS_ADMIN))
+		goto err_out;
+
+	cset = task_css_set(current);
+	get_css_set(cset);
+
+	err = -ENOMEM;
+	new_ns = alloc_cgroup_ns();
+	if (!new_ns)
+		goto err_out;
+
+	new_ns->user_ns = get_user_ns(user_ns);
+	new_ns->root_cset = cset;
+
+	return new_ns;
+
+err_out:
+	if (cset)
+		put_css_set(cset);
+	kfree(new_ns);
+	return ERR_PTR(err);
+}
+
+static int cgroupns_install(struct nsproxy *nsproxy, void *ns)
+{
+	pr_info("setns not supported for cgroup namespace");
+	return -EINVAL;
+}
+
+static struct ns_common *cgroupns_get(struct task_struct *task)
+{
+	struct cgroup_namespace *ns = NULL;
+	struct nsproxy *nsproxy;
+
+	task_lock(task);
+	nsproxy = task->nsproxy;
+	if (nsproxy) {
+		ns = nsproxy->cgroup_ns;
+		get_cgroup_ns(ns);
+	}
+	task_unlock(task);
+
+	return ns ? &ns->ns : NULL;
+}
+
+static void cgroupns_put(struct ns_common *ns)
+{
+	put_cgroup_ns(to_cg_ns(ns));
+}
+
+const struct proc_ns_operations cgroupns_operations = {
+	.name		= "cgroup",
+	.type		= CLONE_NEWCGROUP,
+	.get		= cgroupns_get,
+	.put		= cgroupns_put,
+	.install	= cgroupns_install,
+};
+
+static __init int cgroup_namespaces_init(void)
+{
+	return 0;
+}
+subsys_initcall(cgroup_namespaces_init);
+
 #ifdef CONFIG_CGROUP_DEBUG
 static struct cgroup_subsys_state *
 debug_css_alloc(struct cgroup_subsys_state *parent_css)

@@ -1880,7 +1880,7 @@ static int check_unshare_flags(unsigned long unshare_flags)
 	if (unshare_flags & ~(CLONE_THREAD|CLONE_FS|CLONE_NEWNS|CLONE_SIGHAND|
 				CLONE_VM|CLONE_FILES|CLONE_SYSVSEM|
 				CLONE_NEWUTS|CLONE_NEWIPC|CLONE_NEWNET|
-				CLONE_NEWUSER|CLONE_NEWPID))
+				CLONE_NEWUSER|CLONE_NEWPID|CLONE_NEWCGROUP))
 		return -EINVAL;
 	/*
 	 * Not implemented, but pretend it works if there is nothing

@@ -25,6 +25,7 @@
 #include <linux/proc_ns.h>
 #include <linux/file.h>
 #include <linux/syscalls.h>
+#include <linux/cgroup.h>
 
 static struct kmem_cache *nsproxy_cachep;
 

@@ -39,6 +40,9 @@ struct nsproxy init_nsproxy = {
 #ifdef CONFIG_NET
 	.net_ns			= &init_net,
 #endif
+#ifdef CONFIG_CGROUPS
+	.cgroup_ns		= &init_cgroup_ns,
+#endif
 };
 
 static inline struct nsproxy *create_nsproxy(void)

@@ -92,6 +96,13 @@ static struct nsproxy *create_new_namespaces(unsigned long flags,
 		goto out_pid;
 	}
 
+	new_nsp->cgroup_ns = copy_cgroup_ns(flags, user_ns,
+					    tsk->nsproxy->cgroup_ns);
+	if (IS_ERR(new_nsp->cgroup_ns)) {
+		err = PTR_ERR(new_nsp->cgroup_ns);
+		goto out_cgroup;
+	}
+
 	new_nsp->net_ns = copy_net_ns(flags, user_ns, tsk->nsproxy->net_ns);
 	if (IS_ERR(new_nsp->net_ns)) {
 		err = PTR_ERR(new_nsp->net_ns);

@@ -101,6 +112,9 @@ static struct nsproxy *create_new_namespaces(unsigned long flags,
 	return new_nsp;
 
 out_net:
+	if (new_nsp->cgroup_ns)
+		put_cgroup_ns(new_nsp->cgroup_ns);
+out_cgroup:
 	if (new_nsp->pid_ns_for_children)
 		put_pid_ns(new_nsp->pid_ns_for_children);
 out_pid:

@@ -128,7 +142,8 @@ int copy_namespaces(unsigned long flags, struct task_struct *tsk)
 	struct nsproxy *new_ns;
 
 	if (likely(!(flags & (CLONE_NEWNS | CLONE_NEWUTS | CLONE_NEWIPC |
-			      CLONE_NEWPID | CLONE_NEWNET)))) {
+			      CLONE_NEWPID | CLONE_NEWNET |
+			      CLONE_NEWCGROUP)))) {
 		get_nsproxy(old_ns);
 		return 0;
 	}

@@ -165,6 +180,8 @@ void free_nsproxy(struct nsproxy *ns)
 		put_ipc_ns(ns->ipc_ns);
 	if (ns->pid_ns_for_children)
 		put_pid_ns(ns->pid_ns_for_children);
+	if (ns->cgroup_ns)
+		put_cgroup_ns(ns->cgroup_ns);
 	put_net(ns->net_ns);
 	kmem_cache_free(nsproxy_cachep, ns);
 }

@@ -180,7 +197,7 @@ int unshare_nsproxy_namespaces(unsigned long unshare_flags,
 	int err = 0;
 
 	if (!(unshare_flags & (CLONE_NEWNS | CLONE_NEWUTS | CLONE_NEWIPC |
-			       CLONE_NEWNET | CLONE_NEWPID)))
+			       CLONE_NEWNET | CLONE_NEWPID | CLONE_NEWCGROUP)))
 		return 0;
 
 	user_ns = new_cred ? new_cred->user_ns : current_user_ns();

@@ -44,28 +44,123 @@ static int kernfs_name_locked(struct kernfs_node *kn, char *buf, size_t buflen)
 	return strlcpy(buf, kn->parent ? kn->name : "/", buflen);
 }
 
-static char * __must_check kernfs_path_locked(struct kernfs_node *kn, char *buf,
-					      size_t buflen)
+/* kernfs_node_depth - compute depth from @from to @to */
+static size_t kernfs_depth(struct kernfs_node *from, struct kernfs_node *to)
 {
-	char *p = buf + buflen;
-	int len;
+	size_t depth = 0;
 
-	*--p = '\0';
+	while (to->parent && to != from) {
+		depth++;
+		to = to->parent;
+	}
+	return depth;
+}
 
-	do {
-		len = strlen(kn->name);
-		if (p - buf < len + 1) {
-			buf[0] = '\0';
-			p = NULL;
-			break;
-		}
-		p -= len;
-		memcpy(p, kn->name, len);
-		*--p = '/';
-		kn = kn->parent;
-	} while (kn && kn->parent);
+static struct kernfs_node *kernfs_common_ancestor(struct kernfs_node *a,
+						  struct kernfs_node *b)
+{
+	size_t da, db;
+	struct kernfs_root *ra = kernfs_root(a), *rb = kernfs_root(b);
+
+	if (ra != rb)
+		return NULL;
+
+	da = kernfs_depth(ra->kn, a);
+	db = kernfs_depth(rb->kn, b);
+
+	while (da > db) {
+		a = a->parent;
+		da--;
+	}
+	while (db > da) {
+		b = b->parent;
+		db--;
+	}
+
+	/* worst case b and a will be the same at root */
+	while (b != a) {
+		b = b->parent;
+		a = a->parent;
+	}
+
+	return a;
+}
+
+/**
+ * kernfs_path_from_node_locked - find a pseudo-absolute path to @kn_to,
+ * where kn_from is treated as root of the path.
+ * @kn_from: kernfs node which should be treated as root for the path
+ * @kn_to: kernfs node to which path is needed
+ * @buf: buffer to copy the path into
+ * @buflen: size of @buf
+ *
+ * We need to handle couple of scenarios here:
+ * [1] when @kn_from is an ancestor of @kn_to at some level
+ * kn_from: /n1/n2/n3
+ * kn_to:   /n1/n2/n3/n4/n5
+ * result:  /n4/n5
+ *
+ * [2] when @kn_from is on a different hierarchy and we need to find common
+ * ancestor between @kn_from and @kn_to.
+ * kn_from: /n1/n2/n3/n4
+ * kn_to:   /n1/n2/n5
+ * result:  /../../n5
+ * OR
+ * kn_from: /n1/n2/n3/n4/n5   [depth=5]
+ * kn_to:   /n1/n2/n3         [depth=3]
+ * result:  /../..
+ *
+ * return value: length of the string.  If greater than buflen,
+ * then contents of buf are undefined.  On error, -1 is returned.
+ */
+static int
+kernfs_path_from_node_locked(struct kernfs_node *kn_to,
+			     struct kernfs_node *kn_from, char *buf,
+			     size_t buflen)
+{
+	struct kernfs_node *kn, *common;
+	const char parent_str[] = "/..";
+	size_t depth_from, depth_to, len = 0, nlen = 0;
+	char *p;
+	int i;
+
+	if (!kn_from)
+		kn_from = kernfs_root(kn_to)->kn;
+
+	if (kn_from == kn_to)
+		return strlcpy(buf, "/", buflen);
+
+	common = kernfs_common_ancestor(kn_from, kn_to);
+	if (WARN_ON(!common))
+		return -1;
+
+	depth_to = kernfs_depth(common, kn_to);
+	depth_from = kernfs_depth(common, kn_from);
+
+	if (buf)
+		buf[0] = '\0';
+
+	for (i = 0; i < depth_from; i++)
+		len += strlcpy(buf + len, parent_str,
+			       len < buflen ? buflen - len : 0);
+
+	/* Calculate how many bytes we need for the rest */
+	for (kn = kn_to; kn != common; kn = kn->parent)
+		nlen += strlen(kn->name) + 1;
 
-	return p;
+	if (len + nlen >= buflen)
+		return len + nlen;
+
+	p = buf + len + nlen;
+	*p = '\0';
+	for (kn = kn_to; kn != common; kn = kn->parent) {
+		nlen = strlen(kn->name);
+		p -= nlen;
+		memcpy(p, kn->name, nlen);
+		*(--p) = '/';
+	}
+
+	return len + nlen;
 }
 
 /**

@@ -115,6 +210,34 @@ size_t kernfs_path_len(struct kernfs_node *kn)
 }
 
 /**
+ * kernfs_path_from_node - build path of node @to relative to @from.
+ * @from: parent kernfs_node relative to which we need to build the path
+ * @to: kernfs_node of interest
+ * @buf: buffer to copy @to's path into
+ * @buflen: size of @buf
+ *
+ * Builds @to's path relative to @from in @buf. @from and @to must
+ * be on the same kernfs-root. If @from is not parent of @to, then a relative
+ * path (which includes '..'s) as needed to reach from @from to @to is
+ * returned.
+ * 
+ * If @buf isn't long enough, the return value will be greater than @buflen
+ * and @buf contents are undefined.
+ */
+int kernfs_path_from_node(struct kernfs_node *to, struct kernfs_node *from,
+			  char *buf, size_t buflen)
+{
+	unsigned long flags;
+	int ret;
+
+	spin_lock_irqsave(&kernfs_rename_lock, flags);
+	ret = kernfs_path_from_node_locked(to, from, buf, buflen);
+	spin_unlock_irqrestore(&kernfs_rename_lock, flags);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(kernfs_path_from_node);
+
+/**
  * kernfs_path - build full path of a given node
  * @kn: kernfs_node of interest
  * @buf: buffer to copy @kn's name into

@@ -127,13 +250,12 @@ size_t kernfs_path_len(struct kernfs_node *kn)
  */
 char *kernfs_path(struct kernfs_node *kn, char *buf, size_t buflen)
 {
-	unsigned long flags;
-	char *p;
+	int ret;
 
-	spin_lock_irqsave(&kernfs_rename_lock, flags);
-	p = kernfs_path_locked(kn, buf, buflen);
-	spin_unlock_irqrestore(&kernfs_rename_lock, flags);
-	return p;
+	ret = kernfs_path_from_node(kn, NULL, buf, buflen);
+	if (ret < 0 || ret >= buflen)
+		return NULL;
+	return buf;
 }
 EXPORT_SYMBOL_GPL(kernfs_path);
 

@@ -164,18 +286,39 @@ void pr_cont_kernfs_name(struct kernfs_node *kn)
 void pr_cont_kernfs_path(struct kernfs_node *kn)
 {
 	unsigned long flags;
-	char *p;
+	char *p = NULL;
+	int sz1, sz2;
 
 	spin_lock_irqsave(&kernfs_rename_lock, flags);
 
-	p = kernfs_path_locked(kn, kernfs_pr_cont_buf,
-			       sizeof(kernfs_pr_cont_buf));
-	if (p)
-		pr_cont("%s", p);
-	else
-		pr_cont("<name too long>");
+	sz1 = kernfs_path_from_node_locked(kn, NULL, kernfs_pr_cont_buf,
+					   sizeof(kernfs_pr_cont_buf));
+	if (sz1 < 0) {
+		pr_cont("(error)");
+		goto out;
+	}
+
+	if (sz1 < sizeof(kernfs_pr_cont_buf)) {
+		pr_cont("%s", kernfs_pr_cont_buf);
+		goto out;
+	}
+
+	p = kmalloc(sz1 + 1, GFP_NOFS);
+	if (!p) {
+		pr_cont("(out of memory)");
+		goto out;
+	}
+	sz2 = kernfs_path_from_node_locked(kn, NULL, p, sz1 + 1);
+	if (sz2 > sz1 || sz2 < 0) {
+		pr_cont("(error)");
+		goto out;
+	}
+
+	pr_cont("%s", p);
 
+out:
 	spin_unlock_irqrestore(&kernfs_rename_lock, flags);
+	kfree(p);
 }
 
 /**

@@ -267,8 +267,9 @@ static inline bool kernfs_ns_enabled(struct kernfs_node *kn)
 
 int kernfs_name(struct kernfs_node *kn, char *buf, size_t buflen);
 size_t kernfs_path_len(struct kernfs_node *kn);
-char * __must_check kernfs_path(struct kernfs_node *kn, char *buf,
-				size_t buflen);
+int kernfs_path_from_node(struct kernfs_node *root_kn, struct kernfs_node *kn,
+			  char *buf, size_t buflen);
+char *kernfs_path(struct kernfs_node *kn, char *buf, size_t buflen);
 void pr_cont_kernfs_name(struct kernfs_node *kn);
 void pr_cont_kernfs_path(struct kernfs_node *kn);
 struct kernfs_node *kernfs_get_parent(struct kernfs_node *kn);

@@ -338,8 +339,8 @@ static inline int kernfs_name(struct kernfs_node *kn, char *buf, size_t buflen)
 static inline size_t kernfs_path_len(struct kernfs_node *kn)
 { return 0; }
 
-static inline char * __must_check kernfs_path(struct kernfs_node *kn, char *buf,
-					      size_t buflen)
+static inline char *kernfs_path(struct kernfs_node *kn, char *buf,
+				size_t buflen)
 { return NULL; }
 
 static inline void pr_cont_kernfs_name(struct kernfs_node *kn) { }