linux-kernel - Re: [RFC][PATCH 0/3] vfs: Detach mounts on unlink.

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Message-ID: <CA+55aFxgUMnZts-RXFh1qL1u+De_HNdMrC34skyWurbzvqpUdg@mail.gmail.com>
Date:	Sat, 5 Oct 2013 16:22:15 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Rob Landley <rob@...dley.net>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Miklos Szeredi <miklos@...redi.hu>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Linux-Fsdevel <linux-fsdevel@...r.kernel.org>,
	Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andy Lutomirski <luto@...capital.net>
Subject: Re: [RFC][PATCH 0/3] vfs: Detach mounts on unlink.

On Sat, Oct 5, 2013 at 4:17 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> So learn this pattern: every time you use chroot, add a simple
>
>   chdir("/");
>
> immediately after the chroot call.

.. btw, also make sure that you close all non-essential file
descriptors. Having any open directory file descriptors pointing to
outside the chroot is also a classic escape.

Even then, escaping chroot is usually fairly easy. Making a
escape-proof chroot is really quite hard. Basically impossible if you
allow root.

                 Linus
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