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);
+}