From mboxrd@z Thu Jan  1 00:00:00 1970
From: ebiederm@xmission.com (Eric W. Biederman)
Subject: [PATCH review 1/8] dcache: Handle escaped paths in prepend_path
Date: Thu, 13 Aug 2015 23:30:16 -0500
Message-ID: <87r3n6jxuv.fsf_-_@x220.int.ebiederm.org>
References: <871tncuaf6.fsf@x220.int.ebiederm.org>
	<87mw5xq7lt.fsf@x220.int.ebiederm.org>
	<87a8yqou41.fsf_-_@x220.int.ebiederm.org>
	<874moq9oyb.fsf_-_@x220.int.ebiederm.org>
	<871tfkawu9.fsf_-_@x220.int.ebiederm.org>
	<87egjk9i61.fsf_-_@x220.int.ebiederm.org>
	<20150810043637.GC14139@ZenIV.linux.org.uk>
	<877foymrwt.fsf@x220.int.ebiederm.org>
	<87wpwyjxwc.fsf_-_@x220.int.ebiederm.org>
Mime-Version: 1.0
Content-Type: text/plain
Cc: linux-fsdevel@vger.kernel.org, Al Viro <viro@ZenIV.linux.org.uk>,
	Andy Lutomirski <luto@amacapital.net>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	Richard Weinberger <richard@nod.at>,
	Andrey Vagin <avagin@openvz.org>, Jann Horn <jann@thejh.net>,
	Willy Tarreau <w@1wt.eu>, Omar Sandoval <osandov@osandov.com>,
	Miklos Szeredi <miklos@szeredi.hu>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	"J. Bruce Fields" <bfields@fieldses.org>
To: Linux Containers <containers@lists.linux-foundation.org>
Return-path: <linux-fsdevel-owner@vger.kernel.org>
Received: from out02.mta.xmission.com ([166.70.13.232]:57523 "EHLO
	out02.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1752068AbbHNEhI (ORCPT
	<rfc822;linux-fsdevel@vger.kernel.org>);
	Fri, 14 Aug 2015 00:37:08 -0400
In-Reply-To: <87wpwyjxwc.fsf_-_@x220.int.ebiederm.org> (Eric W. Biederman's
	message of "Thu, 13 Aug 2015 23:29:23 -0500")
Sender: linux-fsdevel-owner@vger.kernel.org
List-ID: <linux-fsdevel.vger.kernel.org>


A rename can result in a dentry that by walking up d_parent
will never reach it's mnt_root.  For lack of a better term
I call this an escaped path.

prepend_path is called by four different functions __d_path,
d_absolute_path, d_path, and getcwd.

__d_path only wants to see paths are connected to the root it passes
in.  So __d_path needs prepend_path to return an error.

d_absolute_path similarly wants to see paths that are connected to
some root.  Escaped paths are not connected to any mnt_root so
d_absolute_path needs prepend_path to return an error greater
than 1.  So escaped paths will be treated like paths on lazily
unmounted mounts.

getcwd needs to prepend "(unreachable)" so getcwd also needs
prepend_path to return an error.

d_path is the interesting hold out.  d_path just wants to print
something, and does not care about the weird cases.  Which raises
the question what should be printed?

Given that <escaped_path>/<anything> should result in -ENOENT I
believe it is desirable for escaped paths to be printed as empty
paths.  As there are not really any meaninful path components when
considered from the perspective of a mount tree.

So tweak prepend_path to return an empty path with an new error
code of 3 when it encounters an escaped path.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
 fs/dcache.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/dcache.c b/fs/dcache.c
index 7a3f3e5f9cea..f762e76e85cc 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -2923,6 +2923,13 @@ restart:
 
 		if (dentry == vfsmnt->mnt_root || IS_ROOT(dentry)) {
 			struct mount *parent = ACCESS_ONCE(mnt->mnt_parent);
+			/* Escaped? */
+			if (dentry != vfsmnt->mnt_root) {
+				bptr = *buffer;
+				blen = *buflen;
+				error = 3;
+				break;
+			}
 			/* Global root? */
 			if (mnt != parent) {
 				dentry = ACCESS_ONCE(mnt->mnt_mountpoint);
-- 
2.2.1