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Subject[PATCH 2/2] containers: implement namespace tracking subsystem (v3)
From 3efbf21565c69fe4dd76b9fcf073f6f9954aa1fa Mon Sep 17 00:00:00 2001
From: Serge E. Hallyn <serue@us.ibm.com>
Date: Tue, 5 Jun 2007 10:25:05 -0400
Subject: [PATCH 2/2] containers: implement namespace tracking subsystem (v3)

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@us.ibm.com>
---
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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