SELINUX: add /sys/fs/selinux mount point to put selinuxfs

In the interest of keeping userspace from having to create new root
filesystems all the time, let's follow the lead of the other in-kernel
filesystems and provide a proper mount point for it in sysfs.

For selinuxfs, this mount point should be in /sys/fs/selinux/

Cc: Stephen Smalley <sds@tycho.nsa.gov>
Cc: James Morris <jmorris@namei.org>
Cc: Eric Paris <eparis@parisplace.org>
Cc: Lennart Poettering <mzerqung@0pointer.de>
Cc: Daniel J Walsh <dwalsh@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
[include kobject.h - Eric Paris]
[use selinuxfs_obj throughout - Eric Paris]
Signed-off-by: Eric Paris <eparis@redhat.com>

security/selinux/selinuxfs.c

@@ -28,6 +28,7 @@
 #include <linux/percpu.h>
 #include <linux/audit.h>
 #include <linux/uaccess.h>
+#include <linux/kobject.h>
 
 /* selinuxfs pseudo filesystem for exporting the security policy API.
    Based on the proc code and the fs/nfsd/nfsctl.c code. */
@@ -1909,6 +1910,7 @@ static struct file_system_type sel_fs_type = {
 };
 
 struct vfsmount *selinuxfs_mount;
+static struct kobject *selinuxfs_kobj;
 
 static int __init init_sel_fs(void)
 {
@@ -1916,9 +1918,16 @@ static int __init init_sel_fs(void)
 
 	if (!selinux_enabled)
 		return 0;
+
+	selinuxfs_kobj = kobject_create_and_add("selinux", fs_kobj);
+	if (!selinuxfs_kobj)
+		return -ENOMEM;
+
 	err = register_filesystem(&sel_fs_type);
-	if (err)
+	if (err) {
+		kobject_put(selinuxfs_kobj);
 		return err;
+	}
 
 	selinuxfs_mount = kern_mount(&sel_fs_type);
 	if (IS_ERR(selinuxfs_mount)) {
@@ -1935,6 +1944,7 @@ __initcall(init_sel_fs);
 #ifdef CONFIG_SECURITY_SELINUX_DISABLE
 void exit_sel_fs(void)
 {
+	kobject_put(selinuxfs_kobj);
 	unregister_filesystem(&sel_fs_type);
 }
 #endif