[RFC][PATCH 5/6] Define helper functions to unshare pid namespace

[sukadev@xxxxxxxxxx]

From: Sukadev Bhattiprolu <sukadev@xxxxxxxxxx>
Subject: [RFC][PATCH 5/6] Define helper functions to unshare pid namespace

Define clone_pid_ns() and unshare_pid_ns() functions that will be
used in the next patch to unshare pid namespace.

Changelog: 
	- Rewrite of orignal code in -lxc from Cedric Le Goater to enforce
	  setsid() requirement on unshare().
	- [Cedric Le Goater comment] Fix minor compile errors/warnings

Signed-off-by: Cedric Le Goater <clg@xxxxxxxxxx>
Signed-off-by: Sukadev Bhattiprolu <sukadev@xxxxxxxxxx>
Cc: Dave Hansen <haveblue@xxxxxxxxxx>
Cc: Serge Hallyn <serue@xxxxxxxxxx>
Cc: containers@xxxxxxxxxxxxxx
---
 include/linux/pid_namespace.h |    2 +
 kernel/pid.c                  |   55 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 57 insertions(+)

Index: lx26-20-mm2b/include/linux/pid_namespace.h
===================================================================
--- lx26-20-mm2b.orig/include/linux/pid_namespace.h	2007-03-09 17:00:14.000000000 -0800
+++ lx26-20-mm2b/include/linux/pid_namespace.h	2007-03-09 17:14:25.000000000 -0800
@@ -29,6 +29,8 @@ static inline void get_pid_ns(struct pid
 	kref_get(&ns->kref);
 }
 
+extern int unshare_pid_ns(unsigned long unshare_ns_flags,
+			struct pid_nr **new_pid_nr);
 extern int copy_pid_ns(int flags, struct task_struct *tsk);
 extern void free_pid_ns(struct kref *kref);
 
Index: lx26-20-mm2b/kernel/pid.c
===================================================================
--- lx26-20-mm2b.orig/kernel/pid.c	2007-03-09 17:03:53.000000000 -0800
+++ lx26-20-mm2b/kernel/pid.c	2007-03-09 17:14:57.000000000 -0800
@@ -298,6 +298,35 @@ pid_t pid_nr(struct pid *pid)
 	return 0;
 }
 
+static struct pid_namespace *clone_pid_ns(void)
+{
+	struct pid_namespace *ns;
+	int i;
+
+	ns = kmalloc(sizeof(struct pid_namespace), GFP_KERNEL);
+	if (!ns)
+		return ns;
+
+	kref_init(&ns->kref);
+
+	atomic_set(&ns->pidmap[0].nr_free, BITS_PER_PAGE - 1);
+	ns->pidmap[0].page = kzalloc(PAGE_SIZE, GFP_KERNEL);
+	if (!ns->pidmap[0].page) {
+		kfree(ns);
+		return NULL;
+	}
+
+	set_bit(0, ns->pidmap[0].page);
+
+	for (i = 1; i < PIDMAP_ENTRIES; i++) {
+		atomic_set(&ns->pidmap[i].nr_free, BITS_PER_PAGE);
+		ns->pidmap[i].page = NULL;
+	}
+	ns->last_pid = 0;
+	ns->child_reaper = current;
+	return ns;
+}
+
 struct pid *alloc_pid(void)
 {
 	struct pid *pid;
@@ -471,6 +500,32 @@ struct pid *find_ge_pid(int nr)
 }
 EXPORT_SYMBOL_GPL(find_get_pid);
 
+int unshare_pid_ns(unsigned long unshare_ns_flags, struct pid_nr **new_pid_nr)
+{
+	struct pid_namespace *pid_ns;
+
+	if (!(unshare_ns_flags & CLONE_NEWPID))
+		return 0;
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
+	if (task_pid(current) != task_session(current))
+		return -EPERM;
+
+	pid_ns = clone_pid_ns();
+	if (!pid_ns)
+		return -ENOMEM;
+
+	*new_pid_nr = alloc_pidmap_pid_nr(pid_ns);
+	if (!*new_pid_nr) {
+		put_pid_ns(pid_ns);
+		return -ENOMEM;
+	}
+
+	return 0;
+}
+
 int copy_pid_ns(int flags, struct task_struct *tsk)
 {
 	struct pid_namespace *old_ns = task_pid_ns(tsk);
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