From: Andy Lutomirski <luto@amacapital.net>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Casey Schaufler <casey@schaufler-ca.com>,
Jamie Lokier <jamie@shareable.org>,
Will Drewry <wad@chromium.org>,
linux-kernel@vger.kernel.org, keescook@chromium.org,
john.johansen@canonical.com, serge.hallyn@canonical.com,
coreyb@linux.vnet.ibm.com, pmoore@redhat.com, eparis@redhat.com,
djm@mindrot.org, segoon@openwall.com, rostedt@goodmis.org,
jmorris@namei.org, scarybeasts@gmail.com, avi@redhat.com,
penberg@cs.helsinki.fi, viro@zeniv.linux.org.uk, mingo@elte.hu,
akpm@linux-foundation.org, khilman@ti.com,
borislav.petkov@amd.com, amwang@redhat.com, oleg@redhat.com,
ak@linux.intel.com, eric.dumazet@gmail.com, gregkh@suse.de,
dhowells@redhat.com, daniel.lezcano@free.fr,
linux-fsdevel@vger.kernel.org,
linux-security-module@vger.kernel.org, olofj@chromium.org,
mhalcrow@google.com, dlaor@redhat.com, corbet@lwn.net,
alan@lxorguk.ukuu.org.uk
Subject: Re: [PATCH 4/4] Allow unprivileged chroot when safe
Date: Sun, 15 Jan 2012 17:08:38 -0800 [thread overview]
Message-ID: <CALCETrUqmiEbQuVVj0bVDExOXgfOi7RAVVj03OkY63biB-ntDw@mail.gmail.com> (raw)
In-Reply-To: <CA+55aFybUcL2M9qZ91MF-PAwNSO6AdEfHXv_i00sftHyTb3ocQ@mail.gmail.com>
On Sun, Jan 15, 2012 at 4:45 PM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
> On Sun, Jan 15, 2012 at 4:37 PM, Andy Lutomirski <luto@amacapital.net> wrote:
>> Chroot can easily be used to subvert setuid programs. If no_new_privs,
>> then setuid programs don't gain any privilege, so allow chroot.
>>
>> Because chroot is an easy way to break out of chroot jail, CAP_SYS_ADMIN
>> is still required if the caller is already chrooted.
>
> So I think this whole chroot thing needs more people looking at it. I
> brought up chroot as an example, but there may be other reasons why
> you don't want user chrooting things than just the setuid confusion.
Agreed. There are plenty of security people cc'd. Thoughts (and
attacks) are welcome!
>
> There's also the whole issue with doing things like local non-root
> bind mounts, which are arguably more useful than chroot, and which are
> disallowed for similar reasons. So I don't think chroot is all that
> special.
They're almost certainly more useful. Binding the tree of your choice
on top of / is a nice (and more secure) way to emulate chroot. The
only downside I've thought of in five minutes is that it would prevent
the administrator from blocking access to a directory by bind-mounting
something on to of it -- an unprivileged non-recursive bind mount of
the containing filesystem would get the hidden directory back. I'm
not sure this is a real problem.
--Andy
next prev parent reply other threads:[~2012-01-16 1:09 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-16 0:37 [PATCH v2 0/4] PR_SET_NO_NEW_PRIVS, unshare, and chroot Andy Lutomirski
2012-01-16 0:37 ` [PATCH v2 1/4] Add PR_{GET,SET}_NO_NEW_PRIVS to prevent execve from granting privs Andy Lutomirski
2012-01-16 17:33 ` Oleg Nesterov
2012-01-16 20:15 ` Andy Lutomirski
2012-01-16 0:37 ` [PATCH v2 2/4] Fix apparmor for PR_{GET,SET}_NO_NEW_PRIVS Andy Lutomirski
2012-01-16 0:37 ` [PATCH v2 3/4] Allow unprivileged CLONE_NEWUTS and CLONE_NEWIPC with no_new_privs Andy Lutomirski
2012-01-16 0:37 ` [PATCH 4/4] Allow unprivileged chroot when safe Andy Lutomirski
2012-01-16 0:45 ` Linus Torvalds
2012-01-16 1:08 ` Andy Lutomirski [this message]
2012-01-16 19:26 ` Colin Walters
2012-01-16 20:18 ` Andy Lutomirski
2012-01-17 10:14 ` Jamie Lokier
2012-01-16 20:06 ` Al Viro
2012-01-16 20:15 ` Andy Lutomirski
2012-01-16 20:26 ` Al Viro
2012-01-17 16:23 ` Oleg Nesterov
2012-01-17 16:31 ` Andy Lutomirski
2012-01-16 1:04 ` [PATCH v2 0/4] PR_SET_NO_NEW_PRIVS, unshare, and chroot Andy Lutomirski
2012-01-16 20:49 ` Colin Walters
2012-01-16 21:25 ` Andy Lutomirski
2012-01-16 21:47 ` Colin Walters
2012-01-16 21:57 ` Andy Lutomirski
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