[PATCH 2/2] containers: implement namespace tracking subsystem (v3)

[Serge E . Hallyn]

When a task enters a new namespace via a clone() or unshare(), a
new container is created and the task moves into it.

This version names containers which are automatically created
using container_clone() as "node_<pid>" where pid is the pid of
the unsharing or cloned process.  (Thanks Pavel for the idea)
This is safe because if the process unshares again, it will
create
	/containers/(...)/node_<pid>/node_<pid>

The only possibilities (AFAICT) for a -EEXIST on unshare are
	1. pid wraparound
	2. a process fails an unshare, then tries again.
Case 1 is unlikely enough that I ignore it (at least for now).
In case 2, the node_<pid> will be empty and can be rmdir'ed to
make the subsequent unshare() succeed.

Changelog:
	Name cloned containers as "node_<pid>".

(no idea where to start versioning, calling this v3 "at random")

Signed-off-by: Serge E. Hallyn <serue@xxxxxxxxxx>
---
 include/linux/container_subsys.h |    6 ++
 include/linux/nsproxy.h          |    7 +++
 init/Kconfig                     |    9 ++++
 kernel/Makefile                  |    1 +
 kernel/container.c               |   23 +++++----
 kernel/ns_container.c            |   99 ++++++++++++++++++++++++++++++++++++++
 kernel/nsproxy.c                 |   16 ++++++
 7 files changed, 152 insertions(+), 9 deletions(-)
 create mode 100644 kernel/ns_container.c

diff --git a/include/linux/container_subsys.h b/include/linux/container_subsys.h
index 8fea7cf..9861751 100644
--- a/include/linux/container_subsys.h
+++ b/include/linux/container_subsys.h
@@ -24,3 +24,9 @@ SUBSYS(debug)
 #endif
 
 /* */
+
+#ifdef CONFIG_CONTAINER_NS
+SUBSYS(ns)
+#endif
+
+/* */
diff --git a/include/linux/nsproxy.h b/include/linux/nsproxy.h
index 189e0dc..8be975b 100644
--- a/include/linux/nsproxy.h
+++ b/include/linux/nsproxy.h
@@ -54,4 +54,11 @@ static inline void exit_task_namespaces(struct task_struct *p)
 		put_nsproxy(ns);
 	}
 }
+
+#ifdef CONFIG_CONTAINER_NS
+int ns_container_clone(struct task_struct *tsk);
+#else
+static inline int ns_container_clone(struct task_struct *tsk) { return 0; }
+#endif
+
 #endif
diff --git a/init/Kconfig b/init/Kconfig
index 5861ad9..d79c505 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -355,6 +355,15 @@ config CONTAINER_CPUACCT
 	  Provides a simple Resource Controller for monitoring the
 	  total CPU consumed by the tasks in a container
 
+config CONTAINER_NS
+        bool "Namespace container subsystem"
+        select CONTAINERS
+        help
+          Provides a simple namespace container subsystem to
+          provide hierarchical naming of sets of namespaces,
+          for instance virtual servers and checkpoint/restart
+          jobs.
+
 config PROC_PID_CPUSET
 	bool "Include legacy /proc/<pid>/cpuset file"
 	depends on CPUSETS
diff --git a/kernel/Makefile b/kernel/Makefile
index f73b3d3..34f2345 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -40,6 +40,7 @@ obj-$(CONFIG_CONTAINERS) += container.o
 obj-$(CONFIG_CONTAINER_DEBUG) += container_debug.o
 obj-$(CONFIG_CPUSETS) += cpuset.o
 obj-$(CONFIG_CONTAINER_CPUACCT) += cpu_acct.o
+obj-$(CONFIG_CONTAINER_NS) += ns_container.o
 obj-$(CONFIG_IKCONFIG) += configs.o
 obj-$(CONFIG_STOP_MACHINE) += stop_machine.o
 obj-$(CONFIG_AUDIT) += audit.o auditfilter.o
diff --git a/kernel/container.c b/kernel/container.c
index 28badda..07802b8 100644
--- a/kernel/container.c
+++ b/kernel/container.c
@@ -2295,12 +2295,6 @@ void container_exit(struct task_struct *tsk, int run_callbacks)
 		put_css_group_taskexit(cg);
 }
 
-static atomic_t namecnt;
-static void get_unused_name(char *buf)
-{
-	sprintf(buf, "node%d", atomic_inc_return(&namecnt));
-}
-
 /**
  * container_clone - duplicate the current container in the hierarchy
  * that the given subsystem is attached to, and move this task into
@@ -2310,7 +2304,7 @@ int container_clone(struct task_struct *tsk, struct container_subsys *subsys)
 {
 	struct dentry *dentry;
 	int ret = 0;
-	char nodename[32];
+	char nodename[MAX_CONTAINER_TYPE_NAMELEN];
 	struct container *parent, *child;
 	struct inode *inode;
 	struct css_group *cg;
@@ -2334,6 +2328,9 @@ int container_clone(struct task_struct *tsk, struct container_subsys *subsys)
 	}
 	cg = tsk->containers;
 	parent = task_container(tsk, subsys->subsys_id);
+
+	snprintf(nodename, MAX_CONTAINER_TYPE_NAMELEN, "node_%d", tsk->pid);
+
 	/* Pin the hierarchy */
 	atomic_inc(&parent->root->sb->s_active);
 
@@ -2342,7 +2339,6 @@ int container_clone(struct task_struct *tsk, struct container_subsys *subsys)
 	mutex_unlock(&container_mutex);
 
 	/* Now do the VFS work to create a container */
-	get_unused_name(nodename);
 	inode = parent->dentry->d_inode;
 
 	/* Hold the parent directory mutex across this operation to
@@ -2415,8 +2411,14 @@ int container_clone(struct task_struct *tsk, struct container_subsys *subsys)
 	return ret;
 }
 
-/* See if "cont" is a descendant of the current task's container in
+/*
+ * See if "cont" is a descendant of the current task's container in
  * the appropriate hierarchy
+ *
+ * If we are sending in dummytop, then presumably we are creating
+ * the top container in the subsystem.
+ *
+ * Called only by the ns (nsproxy) container.
  */
 int container_is_descendant(const struct container *cont)
 {
@@ -2424,6 +2426,9 @@ int container_is_descendant(const struct container *cont)
 	struct container *target;
 	int subsys_id;
 
+	if (cont == dummytop)
+		return 1;
+
 	get_first_subsys(cont, NULL, &subsys_id);
 	target = task_container(current, subsys_id);
 	while (cont != target && cont!= cont->top_container)
diff --git a/kernel/ns_container.c b/kernel/ns_container.c
new file mode 100644
index 0000000..fc12b47
--- /dev/null
+++ b/kernel/ns_container.c
@@ -0,0 +1,99 @@
+/*
+ * ns_container.c - namespace container subsystem
+ *
+ * Copyright 2006, 2007 IBM Corp
+ */
+
+#include <linux/module.h>
+#include <linux/container.h>
+#include <linux/fs.h>
+
+struct ns_container {
+	struct container_subsys_state css;
+	spinlock_t lock;
+};
+
+struct container_subsys ns_subsys;
+
+static inline struct ns_container *container_to_ns(
+		struct container *container)
+{
+	return container_of(container_subsys_state(container, ns_subsys_id),
+			    struct ns_container, css);
+}
+
+int ns_container_clone(struct task_struct *task)
+{
+	return container_clone(task, &ns_subsys);
+}
+
+/*
+ * Rules:
+ *   1. you can only enter a container which is a child of your current
+ *     container
+ *   2. you can only place another process into a container if
+ *     a. you have CAP_SYS_ADMIN
+ *     b. your container is an ancestor of task's destination container
+ *       (hence either you are in the same container as task, or in an
+ *        ancestor container thereof)
+ */
+static int ns_can_attach(struct container_subsys *ss,
+		struct container *new_container, struct task_struct *task)
+{
+	struct container *orig;
+
+	if (current != task) {
+		if (!capable(CAP_SYS_ADMIN))
+			return -EPERM;
+
+		if (!container_is_descendant(new_container))
+			return -EPERM;
+	}
+
+	if (atomic_read(&new_container->count) != 0)
+		return -EPERM;
+
+	orig = task_container(task, ns_subsys_id);
+	if (orig && orig != new_container->parent)
+		return -EPERM;
+
+	return 0;
+}
+
+/*
+ * Rules: you can only create a container if
+ *     1. you are capable(CAP_SYS_ADMIN)
+ *     2. the target container is a descendant of your own container
+ */
+static int ns_create(struct container_subsys *ss, struct container *container)
+{
+	struct ns_container *ns_container;
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+	if (!container_is_descendant(container))
+		return -EPERM;
+
+	ns_container = kzalloc(sizeof(*ns_container), GFP_KERNEL);
+	if (!ns_container) return -ENOMEM;
+	spin_lock_init(&ns_container->lock);
+	container->subsys[ns_subsys.subsys_id] = &ns_container->css;
+	return 0;
+}
+
+static void ns_destroy(struct container_subsys *ss,
+			struct container *container)
+{
+	struct ns_container *ns_container;
+
+	ns_container = container_to_ns(container);
+	kfree(ns_container);
+}
+
+struct container_subsys ns_subsys = {
+	.name = "ns",
+	.can_attach = ns_can_attach,
+	.create = ns_create,
+	.destroy  = ns_destroy,
+	.subsys_id = ns_subsys_id,
+};
diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
index 1bc4b55..afce808 100644
--- a/kernel/nsproxy.c
+++ b/kernel/nsproxy.c
@@ -124,7 +124,14 @@ int copy_namespaces(int flags, struct task_struct *tsk)
 		goto out;
 	}
 
+	err = ns_container_clone(tsk);
+	if (err) {
+		put_nsproxy(new_ns);
+		goto out;
+	}
+
 	tsk->nsproxy = new_ns;
+
 out:
 	put_nsproxy(old_ns);
 	return err;
@@ -177,6 +184,15 @@ int unshare_nsproxy_namespaces(unsigned long unshare_flags,
 	if (IS_ERR(*new_nsp)) {
 		err = PTR_ERR(*new_nsp);
 		put_nsproxy(old_ns);
+		goto out;
+	}
+
+	err = ns_container_clone(current);
+	if (err) {
+		put_nsproxy(*new_nsp);
+		put_nsproxy(old_ns);
 	}
+
+out:
 	return err;
 }
-- 
1.5.1.1.GIT

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