[RFC][PATCH 7/7]: Enable cloning PTY namespaces

[sukadev@us.ibm.com]

From: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Subject: [RFC][PATCH 7/7]: Enable cloning PTY namespaces

Enable cloning PTY namespaces.

Note:
	We are out of clone_flags! This patch depends on Cedric Le Goater's
	clone64() patchset.

Changelog[v2]:
	[Serge Hallyn]: Use rcu to access sb->s_fs_info.

Signed-off-by: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Signed-off-by: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: Matt Helsley <matthltc@us.ibm.com>

---
 fs/devpts/inode.c         |   84 ++++++++++++++++++++++++++++++++++++++++++++--
 include/linux/devpts_fs.h |   22 ++++++++++--
 include/linux/init_task.h |    1 
 include/linux/nsproxy.h   |    2 +
 include/linux/sched.h     |    1 
 kernel/fork.c             |    2 -
 kernel/nsproxy.c          |   17 ++++++++-
 7 files changed, 122 insertions(+), 7 deletions(-)

Index: 2.6.25-rc8-mm1/include/linux/sched.h
===================================================================
--- 2.6.25-rc8-mm1.orig/include/linux/sched.h	2008-04-08 13:38:08.000000000 -0700
+++ 2.6.25-rc8-mm1/include/linux/sched.h	2008-04-08 14:27:41.000000000 -0700
@@ -28,6 +28,7 @@
 #define CLONE_NEWPID		0x20000000	/* New pid namespace */
 #define CLONE_NEWNET		0x40000000	/* New network namespace */
 #define CLONE_IO		0x80000000	/* Clone io context */
+#define CLONE_NEWPTS		0x0000000200000000ULL	/* Clone pts ns */
 
 /*
  * Scheduling policies
Index: 2.6.25-rc8-mm1/include/linux/nsproxy.h
===================================================================
--- 2.6.25-rc8-mm1.orig/include/linux/nsproxy.h	2008-04-08 13:38:08.000000000 -0700
+++ 2.6.25-rc8-mm1/include/linux/nsproxy.h	2008-04-08 14:27:41.000000000 -0700
@@ -8,6 +8,7 @@ struct mnt_namespace;
 struct uts_namespace;
 struct ipc_namespace;
 struct pid_namespace;
+struct pts_namespace;
 
 /*
  * A structure to contain pointers to all per-process
@@ -29,6 +30,7 @@ struct nsproxy {
 	struct pid_namespace *pid_ns;
 	struct user_namespace *user_ns;
 	struct net 	     *net_ns;
+	struct pts_namespace *pts_ns;
 };
 extern struct nsproxy init_nsproxy;
 
Index: 2.6.25-rc8-mm1/include/linux/init_task.h
===================================================================
--- 2.6.25-rc8-mm1.orig/include/linux/init_task.h	2008-04-08 13:38:08.000000000 -0700
+++ 2.6.25-rc8-mm1/include/linux/init_task.h	2008-04-08 14:27:41.000000000 -0700
@@ -78,6 +78,7 @@ extern struct nsproxy init_nsproxy;
 	.mnt_ns		= NULL,						\
 	INIT_NET_NS(net_ns)                                             \
 	INIT_IPC_NS(ipc_ns)						\
+	.pts_ns		= &init_pts_ns,					\
 	.user_ns	= &init_user_ns,				\
 }
 
Index: 2.6.25-rc8-mm1/include/linux/devpts_fs.h
===================================================================
--- 2.6.25-rc8-mm1.orig/include/linux/devpts_fs.h	2008-04-08 13:38:08.000000000 -0700
+++ 2.6.25-rc8-mm1/include/linux/devpts_fs.h	2008-04-08 14:27:41.000000000 -0700
@@ -31,7 +31,7 @@ extern struct pts_namespace init_pts_ns;
 
 static inline struct pts_namespace *current_pts_ns(void)
 {
-	return &init_pts_ns;
+	return current->nsproxy->pts_ns;
 }
 
 static inline struct pts_namespace *pts_ns_from_inode(struct inode *inode)
@@ -61,7 +61,8 @@ struct tty_struct *devpts_get_tty(struct
 /* unlink */
 void devpts_pty_kill(struct pts_namespace *pts_ns, int number);
 
-static inline void free_pts_ns(struct kref *ns_kref) { }
+extern struct pts_namespace *new_pts_ns(void);
+extern void free_pts_ns(struct kref *kref);
 
 static inline struct pts_namespace *get_pts_ns(struct pts_namespace *ns)
 {
@@ -75,6 +76,15 @@ static inline void put_pts_ns(struct pts
 		kref_put(&ns->kref, free_pts_ns);
 }
 
+static inline struct pts_namespace *copy_pts_ns(u64 flags,
+              struct pts_namespace *old_ns)
+{
+      if (flags & CLONE_NEWPTS)
+              return new_pts_ns();
+      else
+              return get_pts_ns(old_ns);
+}
+
 #else
 
 /* Dummy stubs in the no-pty case */
@@ -90,6 +100,14 @@ static inline struct pts_namespace *get_
 }
 
 static inline void put_pts_ns(struct pts_namespace *ns) { }
+
+static inline struct pts_namespace *copy_pts_ns(u64 flags,
+              struct pts_namespace *old_ns)
+{
+      if (flags & CLONE_NEWPTS)
+              return ERR_PTR(-EINVAL);
+      return old_ns;
+}
 #endif
 
 
Index: 2.6.25-rc8-mm1/fs/devpts/inode.c
===================================================================
--- 2.6.25-rc8-mm1.orig/fs/devpts/inode.c	2008-04-08 13:38:08.000000000 -0700
+++ 2.6.25-rc8-mm1/fs/devpts/inode.c	2008-04-08 14:33:04.000000000 -0700
@@ -27,6 +27,7 @@
 
 extern int pty_limit;			/* Config limit on Unix98 ptys */
 static DECLARE_MUTEX(allocated_ptys_lock);
+static struct file_system_type devpts_fs_type;
 
 static struct {
 	int setuid;
@@ -119,6 +120,57 @@ static const struct super_operations dev
 	.show_options	= devpts_show_options,
 };
 
+struct pts_namespace *new_pts_ns(void)
+{
+	struct pts_namespace *ns;
+
+	ns = kmalloc(sizeof(*ns), GFP_KERNEL);
+	if (!ns)
+		return ERR_PTR(-ENOMEM);
+
+	kref_init(&ns->kref);
+
+	ns->mnt = kern_mount_data(&devpts_fs_type, ns);
+	if (IS_ERR(ns->mnt)) {
+		kfree(ns);
+		return ERR_PTR(PTR_ERR(ns->mnt));
+	}
+
+	idr_init(&ns->allocated_ptys);
+
+	printk(KERN_NOTICE "Created pts-ns 0x%p\n", ns);
+
+	return ns;
+}
+
+void free_pts_ns(struct kref *ns_kref)
+{
+	struct pts_namespace *ns;
+
+	ns = container_of(ns_kref, struct pts_namespace, kref);
+
+	/*
+	 * Clear s_fs_info here rather than in ->kill_sb(), since the pts_ns
+	 * is invalid real soon now, but the ->kill_sb() will not happen
+	 * until the last mntput(). And if some one is accessing this
+	 * devpts mount from an ancestor pts ns, we may not be holding
+	 * the last reference to this mnt.
+	 *
+	 * After clearing the pts_ns is NULL here, any acceses from parent
+	 * will fail.
+	 */
+	rcu_assign_pointer(ns->mnt->mnt_sb->s_fs_info, NULL);
+	mntput(ns->mnt);
+
+	/*
+	 * TODO:
+	 *      idr_remove_all(&ns->allocated_ptys); introduced in 2.6.23
+	 */
+	idr_destroy(&ns->allocated_ptys);
+	kfree(ns);
+
+	printk(KERN_NOTICE "Freed pts-ns 0x%p\n", ns);
+}
 
 static int devpts_mknod(struct inode *dir, struct dentry *dentry,
 			int mode, dev_t rdev)
@@ -217,7 +269,16 @@ static int devpts_test_sb(struct super_b
 
 static int devpts_set_sb(struct super_block *sb, void *data)
 {
-	sb->s_fs_info = data;
+	/*
+	 * new_pts_ns() mounts the pts namespace and free_pts_ns()
+	 * drops the reference to the mount. i.e the s_fs_info is
+	 * cleared and vfsmnt is released _before_ pts_namespace
+	 * is freed.
+	 *
+	 * So we don't need a reference to the pts_namespace here
+	 * (Getting a reference here will also cause circular reference).
+	 */
+	rcu_assign_pointer(sb->s_fs_info, data);
 	return set_anon_super(sb, NULL);
 }
 
@@ -232,7 +293,7 @@ static int devpts_get_sb(struct file_sys
 	if (flags & MS_KERNMOUNT)
 		ns = data;
 	else
-		ns = &init_pts_ns;
+		ns = current_pts_ns();
 
 	/* hereafter we're very simlar to get_sb_nodev */
 	sb = sget(fs_type, devpts_test_sb, devpts_set_sb, ns);
@@ -286,6 +347,13 @@ int devpts_new_index(struct pts_namespac
 	int index;
 	int idr_ret;
 
+	/*
+	 * If pts_ns is NULL, this must be an access from an ancestor-pts-ns
+	 * which happened just as this pts-ns was freed. Fail the access
+	 * from parent-pts-ns.
+	 */
+	if (!pts_ns)
+		return -EAGAIN;
 retry:
 	if (!idr_pre_get(&pts_ns->allocated_ptys, GFP_KERNEL)) {
 		return -ENOMEM;
@@ -311,6 +379,7 @@ retry:
 
 void devpts_kill_index(struct pts_namespace *pts_ns, int idx)
 {
+	BUG_ON(pts_ns == NULL);
 
 	down(&allocated_ptys_lock);
 	idr_remove(&pts_ns->allocated_ptys, idx);
@@ -330,6 +399,7 @@ int devpts_pty_new( struct pts_namespace
 	/* We're supposed to be given the slave end of a pty */
 	BUG_ON(driver->type != TTY_DRIVER_TYPE_PTY);
 	BUG_ON(driver->subtype != PTY_TYPE_SLAVE);
+	BUG_ON(pts_ns == NULL);
 
 	mnt = pts_ns->mnt;
 	root = mnt->mnt_root;
@@ -370,6 +440,14 @@ struct tty_struct *devpts_get_tty(struct
 	struct dentry *dentry;
 	struct tty_struct *tty;
 
+	/*
+	 * If pts_ns is NULL, this must be an access from an ancestor-pts-ns
+	 * which happened just as this pts-ns was freed. Fail the access
+	 * from parent-pts-ns.
+	 */
+	if (!pts_ns)
+		return ERR_PTR(-EAGAIN);
+
 	mnt = pts_ns->mnt;
 
 	dentry = get_node(mnt->mnt_root, number);
@@ -391,6 +469,8 @@ void devpts_pty_kill(struct pts_namespac
 	struct dentry *dentry;
 	struct dentry *root;
 
+	BUG_ON(pts_ns == NULL);
+
 	root = pts_ns->mnt->mnt_root;
 
 	dentry = get_node(root, number);
Index: 2.6.25-rc8-mm1/kernel/fork.c
===================================================================
--- 2.6.25-rc8-mm1.orig/kernel/fork.c	2008-04-08 13:38:08.000000000 -0700
+++ 2.6.25-rc8-mm1/kernel/fork.c	2008-04-08 14:27:41.000000000 -0700
@@ -1714,7 +1714,7 @@ static long do_unshare(u64 unshare_flags
 	if (unshare_flags & ~(CLONE_THREAD|CLONE_FS|CLONE_NEWNS|CLONE_SIGHAND|
 				CLONE_VM|CLONE_FILES|CLONE_SYSVSEM|
 				CLONE_NEWUTS|CLONE_NEWIPC|CLONE_NEWUSER|
-				CLONE_NEWNET))
+				CLONE_NEWNET|CLONE_NEWPTS))
 		goto bad_unshare_out;
 
 	if ((err = unshare_thread(unshare_flags)))
Index: 2.6.25-rc8-mm1/kernel/nsproxy.c
===================================================================
--- 2.6.25-rc8-mm1.orig/kernel/nsproxy.c	2008-04-08 13:38:08.000000000 -0700
+++ 2.6.25-rc8-mm1/kernel/nsproxy.c	2008-04-08 14:27:41.000000000 -0700
@@ -21,6 +21,7 @@
 #include <linux/utsname.h>
 #include <linux/pid_namespace.h>
 #include <net/net_namespace.h>
+#include <linux/devpts_fs.h>
 #include <linux/ipc_namespace.h>
 
 static struct kmem_cache *nsproxy_cachep;
@@ -93,8 +94,17 @@ static struct nsproxy *create_new_namesp
 		goto out_net;
 	}
 
+	new_nsp->pts_ns = copy_pts_ns(flags, tsk->nsproxy->pts_ns);
+	if (IS_ERR(new_nsp->pts_ns)) {
+		err = PTR_ERR(new_nsp->pts_ns);
+		goto out_pts;
+	}
+
 	return new_nsp;
 
+out_pts:
+	if (new_nsp->net_ns)
+		put_net(new_nsp->net_ns);
 out_net:
 	if (new_nsp->user_ns)
 		put_user_ns(new_nsp->user_ns);
@@ -131,7 +141,8 @@ int copy_namespaces(u64 flags, struct ta
 	get_nsproxy(old_ns);
 
 	if (!(flags & (CLONE_NEWNS | CLONE_NEWUTS | CLONE_NEWIPC |
-				CLONE_NEWUSER | CLONE_NEWPID | CLONE_NEWNET)))
+				CLONE_NEWUSER | CLONE_NEWPID | CLONE_NEWNET |
+				CLONE_NEWPTS)))
 		return 0;
 
 	if (!capable(CAP_SYS_ADMIN)) {
@@ -170,6 +181,8 @@ void free_nsproxy(struct nsproxy *ns)
 		put_pid_ns(ns->pid_ns);
 	if (ns->user_ns)
 		put_user_ns(ns->user_ns);
+	if (ns->pts_ns)
+		put_pts_ns(ns->pts_ns);
 	put_net(ns->net_ns);
 	kmem_cache_free(nsproxy_cachep, ns);
 }
@@ -184,7 +197,7 @@ int unshare_nsproxy_namespaces(u64 unsha
 	int err = 0;
 
 	if (!(unshare_flags & (CLONE_NEWNS | CLONE_NEWUTS | CLONE_NEWIPC |
-			       CLONE_NEWUSER | CLONE_NEWNET)))
+			       CLONE_NEWUSER | CLONE_NEWNET | CLONE_NEWPTS)))
 		return 0;
 
 	if (!capable(CAP_SYS_ADMIN))