Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754425AbZL0BFP (ORCPT ); Sat, 26 Dec 2009 20:05:15 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754269AbZL0BFL (ORCPT ); Sat, 26 Dec 2009 20:05:11 -0500 Received: from lists.laptop.org ([18.85.2.145]:45164 "EHLO mail.laptop.org" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754437AbZL0BFE (ORCPT ); Sat, 26 Dec 2009 20:05:04 -0500 Date: Sat, 26 Dec 2009 20:07:08 -0500 From: Michael Stone To: linux-kernel@vger.kernel.org Cc: netdev@vger.kernel.org, linux-security-module@vger.kernel.org, Andi Kleen , David Lang , Oliver Hartkopp , Alan Cox , Herbert Xu , Valdis Kletnieks , Bryan Donlan , Evgeniy Polyakov , "C. Scott Ananian" , James Morris , "Eric W. Biederman" , Bernie Innocenti , Mark Seaborn , Randy Dunlap , =?iso-8859-1?Q?Am=E9rico?= Wang , Tetsuo Handa , Samir Bellabes , Casey Schaufler , "Serge E. Hallyn" , Pavel Machek , Michael Stone Subject: [PATCH 3/3] Security: Document disablenetwork. (v4) Message-ID: <20091227010708.GA12216@heat> References: <20091227010441.GA12077@heat> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20091227010441.GA12077@heat> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3705 Lines: 108 Explain the purpose, implementation, and semantics of the disablenetwork facility. Also reference some example userland clients. Signed-off-by: Michael Stone --- Documentation/disablenetwork.txt | 84 ++++++++++++++++++++++++++++++++++++++ 1 files changed, 84 insertions(+), 0 deletions(-) create mode 100644 Documentation/disablenetwork.txt diff --git a/Documentation/disablenetwork.txt b/Documentation/disablenetwork.txt new file mode 100644 index 0000000..c885502 --- /dev/null +++ b/Documentation/disablenetwork.txt @@ -0,0 +1,84 @@ +Disablenetwork Purpose +---------------------- + +Daniel Bernstein has observed [1] that security-conscious userland processes +may benefit from the ability to irrevocably remove their ability to create, +bind, connect to, or send messages except in the case of previously connected +sockets or AF_UNIX filesystem sockets. + +This facility is particularly attractive to security platforms like OLPC +Bitfrost [2] and to isolation programs like Rainbow [3] and Plash [4] because: + + * it integrates well with standard techniques for writing privilege-separated + Unix programs + + * it integrates well with the need to perform limited socket I/O, e.g., when + running X clients + + * it's available to unprivileged programs + + * it's a discretionary feature available to all of distributors, + administrators, authors, and users + + * its effect is entirely local, rather than global (like netfilter) + + * it's simple enough to have some hope of being used correctly + + +Implementation +-------------- + +The initial userland interface for accessing the disablenetwork functionality +is provided through the prctl() framework via a new pair of options named +PR_{GET,SET}_NETWORK and a new flag named PR_NETWORK_OFF. + +The PR_{GET,SET}_NETWORK options access and modify a new (conditionally +compiled) task_struct flags field named "network". + +Finally, the pre-existing + + security_socket_create(), + security_socket_bind(), + security_socket_connect(), + security_socket_sendmsg(), and + security_ptrace_access_check() + +security hooks are modified to call the corresponding disablenetwork_* +discretionary access control functions. These functions return -EPERM or 0 as +described below. + +Semantics +--------- + +current->network is a task_struct flags field which is preserved across all +variants of fork() and exec(). + +Writes which attempt to clear bits in current->network return -EPERM. + +The default value for current->network is named PR_NETWORK_ON and is defined +to be 0. + +Presently, only one flag is defined: PR_NETWORK_OFF. + +More flags may be defined in the future if they become needed. + +Attempts to set undefined flags result in -EINVAL. + +When PR_NETWORK_OFF is set, the disablenetwork security hooks for socket(), +bind(), connect(), sendmsg(), and ptrace() will return -EPERM or 0. + +Exceptions are made for + + * processes manipulating an AF_UNIX socket or, + * processes calling sendmsg() on a previously connected socket + (i.e. one with msg.msg_name == NULL && msg.msg_namelen == 0) or + * processes calling ptrace() on a target process which shares every + networking restriction flag set in current->network. + +References +---------- + +[1]: http://cr.yp.to/unix/disablenetwork.html +[2]: http://wiki.laptop.org/go/OLPC_Bitfrost +[3]: http://wiki.laptop.org/go/Rainbow +[4]: http://plash.beasts.org/ -- 1.6.6.rc2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/