All of lore.kernel.org
 help / color / mirror / Atom feed
From: Richard Weinberger <richard@nod.at>
To: "netdev@vger.kernel.org" <netdev@vger.kernel.org>
Cc: bridge@lists.linux-foundation.org,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"keescook@chromium.org" <keescook@chromium.org>,
	"kernel-hardening@lists.openwall.com"
	<kernel-hardening@lists.openwall.com>
Subject: [Bridge] user controllable usermodehelper in br_stp_if.c
Date: Sun, 29 Nov 2015 23:43:09 +0100	[thread overview]
Message-ID: <565B7F7D.80208@nod.at> (raw)

Hi!

By spawning new network and user namesapces an unprivileged user
is able to execute /sbin/bridge-stp within the initial mount namespace
with global root rights.
While this cannot directly be used to break out of a container or gain
global root rights it could be used by exploit writers as valuable building block.

e.g.
$ unshare -U -r -n /bin/sh
$ brctl addbr br0
$ brctl stp br0 on # this will execute /sbin/bridge-stp

As this mechanism clearly cannot work with containers and seems to be legacy code
I suggest not calling call_usermodehelper() at all if we're not in the initial user namespace.
What do you think?

Thanks,
//richard

WARNING: multiple messages have this Message-ID (diff)
From: Richard Weinberger <richard@nod.at>
To: "netdev@vger.kernel.org" <netdev@vger.kernel.org>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"kernel-hardening@lists.openwall.com"
	<kernel-hardening@lists.openwall.com>,
	"keescook@chromium.org" <keescook@chromium.org>,
	bridge@lists.linux-foundation.org,
	Stephen Hemminger <stephen@networkplumber.org>
Subject: [kernel-hardening] user controllable usermodehelper in br_stp_if.c
Date: Sun, 29 Nov 2015 23:43:09 +0100	[thread overview]
Message-ID: <565B7F7D.80208@nod.at> (raw)

Hi!

By spawning new network and user namesapces an unprivileged user
is able to execute /sbin/bridge-stp within the initial mount namespace
with global root rights.
While this cannot directly be used to break out of a container or gain
global root rights it could be used by exploit writers as valuable building block.

e.g.
$ unshare -U -r -n /bin/sh
$ brctl addbr br0
$ brctl stp br0 on # this will execute /sbin/bridge-stp

As this mechanism clearly cannot work with containers and seems to be legacy code
I suggest not calling call_usermodehelper() at all if we're not in the initial user namespace.
What do you think?

Thanks,
//richard

WARNING: multiple messages have this Message-ID (diff)
From: Richard Weinberger <richard@nod.at>
To: "netdev@vger.kernel.org" <netdev@vger.kernel.org>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"kernel-hardening@lists.openwall.com" 
	<kernel-hardening@lists.openwall.com>,
	"keescook@chromium.org" <keescook@chromium.org>,
	bridge@lists.linux-foundation.org,
	Stephen Hemminger <stephen@networkplumber.org>
Subject: user controllable usermodehelper in br_stp_if.c
Date: Sun, 29 Nov 2015 23:43:09 +0100	[thread overview]
Message-ID: <565B7F7D.80208@nod.at> (raw)

Hi!

By spawning new network and user namesapces an unprivileged user
is able to execute /sbin/bridge-stp within the initial mount namespace
with global root rights.
While this cannot directly be used to break out of a container or gain
global root rights it could be used by exploit writers as valuable building block.

e.g.
$ unshare -U -r -n /bin/sh
$ brctl addbr br0
$ brctl stp br0 on # this will execute /sbin/bridge-stp

As this mechanism clearly cannot work with containers and seems to be legacy code
I suggest not calling call_usermodehelper() at all if we're not in the initial user namespace.
What do you think?

Thanks,
//richard

WARNING: multiple messages have this Message-ID (diff)
From: Richard Weinberger <richard@nod.at>
To: "netdev@vger.kernel.org" <netdev@vger.kernel.org>
Cc: bridge@lists.linux-foundation.org,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"keescook@chromium.org" <keescook@chromium.org>,
	"kernel-hardening@lists.openwall.com"
	<kernel-hardening@lists.openwall.com>
Subject: user controllable usermodehelper in br_stp_if.c
Date: Sun, 29 Nov 2015 23:43:09 +0100	[thread overview]
Message-ID: <565B7F7D.80208@nod.at> (raw)

Hi!

By spawning new network and user namesapces an unprivileged user
is able to execute /sbin/bridge-stp within the initial mount namespace
with global root rights.
While this cannot directly be used to break out of a container or gain
global root rights it could be used by exploit writers as valuable building block.

e.g.
$ unshare -U -r -n /bin/sh
$ brctl addbr br0
$ brctl stp br0 on # this will execute /sbin/bridge-stp

As this mechanism clearly cannot work with containers and seems to be legacy code
I suggest not calling call_usermodehelper() at all if we're not in the initial user namespace.
What do you think?

Thanks,
//richard

             reply	other threads:[~2015-11-29 22:43 UTC|newest]

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-11-29 22:43 Richard Weinberger [this message]
2015-11-29 22:43 ` user controllable usermodehelper in br_stp_if.c Richard Weinberger
2015-11-29 22:43 ` Richard Weinberger
2015-11-29 22:43 ` [kernel-hardening] " Richard Weinberger
2015-11-30 20:14 ` [Bridge] " Kees Cook
2015-11-30 20:14   ` Kees Cook
2015-11-30 20:14   ` [kernel-hardening] " Kees Cook
2015-11-30 21:38   ` [Bridge] [PATCH net] bridge: Only call /sbin/bridge-stp for the initial network namespace Eric W. Biederman
2015-11-30 21:38     ` Eric W. Biederman
2015-11-30 21:38     ` Eric W. Biederman
2015-11-30 21:38     ` [kernel-hardening] " Eric W. Biederman
2015-11-30 22:12     ` [Bridge] " Stephen Hemminger
2015-11-30 22:12       ` Stephen Hemminger
2015-11-30 22:12       ` Stephen Hemminger
2015-11-30 22:12       ` [kernel-hardening] " Stephen Hemminger
2015-11-30 22:16       ` [Bridge] " Eric W. Biederman
2015-11-30 22:16         ` Eric W. Biederman
2015-11-30 22:16         ` Eric W. Biederman
2015-11-30 22:16         ` [kernel-hardening] " Eric W. Biederman
2015-11-30 22:57     ` [Bridge] " Richard Weinberger
2015-11-30 22:57       ` Richard Weinberger
2015-11-30 22:57       ` Richard Weinberger
2015-11-30 22:57       ` [kernel-hardening] " Richard Weinberger
2015-12-01 14:13     ` [Bridge] " Hannes Frederic Sowa
2015-12-01 14:13       ` Hannes Frederic Sowa
2015-12-01 14:13       ` [kernel-hardening] " Hannes Frederic Sowa
2015-12-03  4:50     ` [Bridge] " David Miller
2015-12-03  4:50       ` David Miller
2015-12-03  4:50       ` David Miller
2015-12-03  4:50       ` [kernel-hardening] " David Miller
2015-12-08 20:56       ` [Bridge] " Kees Cook
2015-12-08 20:56         ` Kees Cook
2015-12-08 20:56         ` [kernel-hardening] " Kees Cook
2015-11-30 23:03   ` [Bridge] user controllable usermodehelper in br_stp_if.c Richard Weinberger
2015-11-30 23:03     ` Richard Weinberger
2015-11-30 23:03     ` Richard Weinberger
2015-11-30 23:03     ` [kernel-hardening] " Richard Weinberger

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=565B7F7D.80208@nod.at \
    --to=richard@nod.at \
    --cc=bridge@lists.linux-foundation.org \
    --cc=keescook@chromium.org \
    --cc=kernel-hardening@lists.openwall.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=netdev@vger.kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.