1 files changed, 43 insertions, 9 deletions

diff --git a/fs/namespace.c b/fs/namespace.c
index e5e1c7d1839b..cfc6d4448aa5 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1048,15 +1048,12 @@ static int show_mountinfo(struct seq_file *m, void *v)
         if (err)
                 goto out;
         seq_putc(m, ' ');
-        seq_path_root(m, &mnt_path, &root, " \t\n\\");
-        if (root.mnt != p->root.mnt || root.dentry != p->root.dentry) {
-                /*
-                 * Mountpoint is outside root, discard that one.  Ugly,
-                 * but less so than trying to do that in iterator in a
-                 * race-free way (due to renames).
-                 */
-                return SEQ_SKIP;
-        }
+
+        /* mountpoints outside of chroot jail will give SEQ_SKIP on this */
+        err = seq_path_root(m, &mnt_path, &root, " \t\n\\");
+        if (err)
+                goto out;
+
         seq_puts(m, mnt->mnt_flags & MNT_READONLY ? " ro" : " rw");
         show_mnt_opts(m, mnt);
 
@@ -2483,11 +2480,43 @@ struct mnt_namespace *create_mnt_ns(struct vfsmount *mnt)
                 __mnt_make_longterm(mnt);
                 new_ns->root = mnt;
                 list_add(&new_ns->list, &new_ns->root->mnt_list);
+        } else {
+                mntput(mnt);
         }
         return new_ns;
 }
 EXPORT_SYMBOL(create_mnt_ns);
 
+struct dentry *mount_subtree(struct vfsmount *mnt, const char *name)
+{
+        struct mnt_namespace *ns;
+        struct super_block *s;
+        struct path path;
+        int err;
+
+        ns = create_mnt_ns(mnt);
+        if (IS_ERR(ns))
+                return ERR_CAST(ns);
+
+        err = vfs_path_lookup(mnt->mnt_root, mnt,
+                        name, LOOKUP_FOLLOW|LOOKUP_AUTOMOUNT, &path);
+
+        put_mnt_ns(ns);
+
+        if (err)
+                return ERR_PTR(err);
+
+        /* trade a vfsmount reference for active sb one */
+        s = path.mnt->mnt_sb;
+        atomic_inc(&s->s_active);
+        mntput(path.mnt);
+        /* lock the sucker */
+        down_write(&s->s_umount);
+        /* ... and return the root of (sub)tree on it */
+        return path.dentry;
+}
+EXPORT_SYMBOL(mount_subtree);
+
 SYSCALL_DEFINE5(mount, char __user *, dev_name, char __user *, dir_name,
                 char __user *, type, unsigned long, flags, void __user *, data)
 {
@@ -2744,3 +2773,8 @@ void kern_unmount(struct vfsmount *mnt)
         }
 }
 EXPORT_SYMBOL(kern_unmount);
+
+bool our_mnt(struct vfsmount *mnt)
+{
+        return check_mnt(mnt);
+}