[RFC PATCH 1/5] nsproxy - refactor setns()

[Ian Kent <ikent@redhat.com>]

For usermode helpers to execute within a namspace a slightly different
entry point to setns() that takes a namspace inode is needed.

Signed-off-by: Ian Kent <ikent@redhat.com>
Cc: Benjamin Coddington <bcodding@redhat.com>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: J. Bruce Fields <bfields@fieldses.org>
Cc: David Howells <dhowells@redhat.com>
Cc: Trond Myklebust <trond.myklebust@primarydata.com>
Cc: Oleg Nesterov <onestero@redhat.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Jeff Layton <jeff.layton@primarydata.com>
---
 include/linux/nsproxy.h |    1 +
 kernel/nsproxy.c        |   21 ++++++++++++++-------
 2 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/include/linux/nsproxy.h b/include/linux/nsproxy.h
index 35fa08f..c75bf12 100644
--- a/include/linux/nsproxy.h
+++ b/include/linux/nsproxy.h
@@ -62,6 +62,7 @@ extern struct nsproxy init_nsproxy;
  *
  */
 
+int setns_inode(struct inode *inode, int nstype);
 int copy_namespaces(unsigned long flags, struct task_struct *tsk);
 void exit_task_namespaces(struct task_struct *tsk);
 void switch_task_namespaces(struct task_struct *tsk, struct nsproxy *new);
diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
index 49746c8..27cc544 100644
--- a/kernel/nsproxy.c
+++ b/kernel/nsproxy.c
@@ -218,20 +218,15 @@ void exit_task_namespaces(struct task_struct *p)
 	switch_task_namespaces(p, NULL);
 }
 
-SYSCALL_DEFINE2(setns, int, fd, int, nstype)
+int setns_inode(struct inode *inode, int nstype)
 {
 	struct task_struct *tsk = current;
 	struct nsproxy *new_nsproxy;
-	struct file *file;
 	struct ns_common *ns;
 	int err;
 
-	file = proc_ns_fget(fd);
-	if (IS_ERR(file))
-		return PTR_ERR(file);
-
 	err = -EINVAL;
-	ns = get_proc_ns(file_inode(file));
+	ns = get_proc_ns(inode);
 	if (nstype && (ns->ops->type != nstype))
 		goto out;
 
@@ -248,6 +243,18 @@ SYSCALL_DEFINE2(setns, int, fd, int, nstype)
 	}
 	switch_task_namespaces(tsk, new_nsproxy);
 out:
+	return err;
+}
+
+SYSCALL_DEFINE2(setns, int, fd, int, nstype)
+{
+	struct file *file;
+	int err;
+
+	file = proc_ns_fget(fd);
+	if (IS_ERR(file))
+		return PTR_ERR(file);
+	err = setns_inode(file_inode(file), nstype);
 	fput(file);
 	return err;
 }