Message-ID: <20071226164230.GA14210@sergelap.austin.ibm.com>
Date:	Wed, 26 Dec 2007 10:42:30 -0600
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:	linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: TOMOYO Linux Security Goal

Quoting Tetsuo Handa (penguin-kernel@...ove.SAKURA.ne.jp):
> This document is intended to specify the security goal that TOMOYO Linux is
> trying to achieve, so that users can evaluate whether TOMOYO Linux will meet
> their needs, and kernel developers can evaluate whether TOMOYO Linux deserved
> to be in-tree.
> 
> 1. About TOMOYO Linux
> 
> Project Homepage: http://tomoyo.sourceforge.jp/index.html.en
> Project Wiki: http://elinux.org/TomoyoLinux
> 
> TOMOYO Linux is a DIY tool for understanding and protecting your system.
> TOMOYO Linux policy definitions are absolutely readable to Linux users, and
> TOMOYO Linux supports unique policy learning mechanism which automatically

Are they in fact unique?

> gathers information and arranges the results as policy definitions.
> These things made it possible for users to write policy from scratch.
> Troubleshooting can be done by users.
> We put some TOMOYO Linux policy examples on our web site.
> 
> http://tomoyo.sourceforge.jp/cgi-bin/lxr/source/etch/domain_policy.conf?v=policy-sample
> 
> 2. TOMOYO Linux Security Goal

This section seems to me to be the most important one, and could really
use a little more detail.

> The TOMOYO Linux's security goal is to provide "MAC that covers practical
> requirements

This email promised me a security goal, but instead of laying out
requirements it meets, its says it meets "practical requirements".
That's really not helpful.

What kernel resources does TOMOYO authorize?  All those which SELinux
does?

> for most users and keeps usable for most administrators".
> TOMOYO Linux is not a tool for security professional but for average users
> and administrators.

So your point was that your main goal is simplicity?

Ok a few things you could add:

	1. Tomoyo provide no sort of information flow control.

	2. TOMOYO is purely restrictive.

	3. Learning mode is primary source of policy so you
	   depend on change of behavior to detect intruders.
	
	4. but any intruder who attempts to do something which
	   the compomised sftware wouldn't have done should be
	   stopped and detected.

This gives a precise (though perhaps wrong as I'm guessing :) picture
of what TOMOYO can do and how it fits in with SMACK, apparmor,
capabilities, and SELinux.

thanks,
-serge

> 3. Our Approach
> 
> To meet the above goal, TOMOYO Linux attempts to make the system where
> everything is prearranged in an easy-to-understand way.
> 
>   * Make the all subject's all access requests that will occur at least once
>     during the lifetime of the kernel known in advance.
> 
>   * Let the administrator understand what access requests will each subject
>     raise in his/her system and write policy which only allows expected and
>     desirable access requests for his/her needs.
> 
> Unlike AppArmor, TOMOYO Linux is intended to protect the whole system from
> attackers exploiting vulnerabilities in applications that the system hosts.
> The threat is that an attacker can cause a vulnerable application to do
> something unexpected and undesirable. TOMOYO Linux addresses this threat by
> recording all applications' behaviors in the test environment and forcing
> all applications behave within recorded behaviors in the production environment.
> 
> TOMOYO Linux has a unique concept of "process invocation history"
> (in short, PIH). The PIH is a developmental lineage of a process.
> When a process executes a program, the process creates a copy with fork() and
> replace the copy with execve().
> TOMOYO Linux appends the pathname of the executed program to the PIH of
> the replaced process, and associates process's PIH (stored in task_struct)
> with a domain.
> As a result, the context switching (a.k.a. domain transition) is unidirectional.
> This rule allows administrator distinguish and manage fine-grained context.
> Domain transition forms tree structure like a directory tree of filesystems.
> Each domain has different set of permissions that are essential for that domain.
> 
> 4. Things you can do with TOMOYO Linux.
> 
> Create policy from scratch.
> 
>   You want to use ready-made policy files supplied by somebody else
>   because testing all paths needed for your usage sounds boring?
> 
>   OK, then you can choose other implementations that provide
>   ready-made policy files, but you should check whether these files
>   contain enough permissions for your usage or not. It is inevitable thing
>   to test all paths needed for your usage if you want to use white listing
>   access control.
> 
>   Also, ready-made policy files tend to contain redundant permissions
>   for your usage which often leads to serious problem.
> 
>   TOMOYO Linux is a DIY tool for understanding and protecting your Linux box.
>   TOMOYO Linux's "learning mode" will automatically generate
>   policy files with necessary and sufficient permissions for you.
> 
> Understand all possible requests.
> 
>   TOMOYO Linux reports what is happening within your Linux box.
>   You can have the security of knowing that no unexpected requests arise,
>   if you have tested all paths needed for your usage.
> 
>   Please remember, we are not saying that
>   "You can have the security of knowing that no unexpected results happen".
>   Although TOMOYO Linux attempts to filter the request as hard as possible,
>   TOMOYO Linux can't guarantee the result.
> 
> Analyze system's behavior.
> 
>   TOMOYO Linux resembles to /usr/bin/strace .
>   TOMOYO Linux reports what programs are executed from each program and
>   what files/networks are accessed by each program.
> 
>   You can use TOMOYO Linux for analyzing application's behavior
>   if you want to know "which configuration file does this daemon read?",
>   "what port numbers does this daemon require?" and so on.
> 
>   This helps debugging program's behaviors and writing manuals.
>   TOMOYO Linux is also applicable for educational use.
> 
> Provide per application firewall.
> 
>   It is userland applications' businesses to perform pathname based access
>   control, but they sometimes make mistakes which are known as OS command
>   injection vulnerability or buffer overflow vulnerability.
>   TOMOYO Linux assists this access control in kernel space to reduce
>   the damage by restricting pathnames which each application can request.
> 
>   TOMOYO Linux can perform TCP_Wrapper-like simple stateless
>   TCP/IP packet filtering based on IPv4/v6 address and ports.
> 
>   TOMOYO Linux can restrict the list of environment variable's name
>   passed to execve() so that some dangerous environment variable
>   (e.g. LD_PRELOAD) won't be passed freely.
> 
>   TOMOYO Linux also supports conditional permissions.
>   You can use uid/gid etc. of a process to restrict the combination of
>   user and accessible resources.
> 
> Provide support for multi-call binary applications without patches.
> 
>   A multi-call binary (e.g. /sbin/busybox) changes behaviors according to
>   the invocation name (in other words, argv[0] passed to execve()).
>   Users specify the invocation name using symbolic links or hard links.
> 
>   TOMOYO Linux allows administrators to give execute permission and define PIH
>   using the pathname of a symbolic link, if the combination of
>   the pathname of a symbolic link and the pathname of the entity pointed
>   by the symbolic link is registered in the policy file.
>   You can use symbolic links as if they are hard links.
> 
>   TOMOYO Linux supports restricting the combination of
>   path-to-executable-or-symbolic-link and basename-of-argv[0]
>   so that users can't pass different argv[0]
>   from path-to-executable-or-symbolic-link freely.
> 
>   Please be aware that some multi-call binary programs change their behaviors
>   according to the command line parameters (i.e. argv[1] to argv[argc - 1]).
>   Regarding such programs, TOMOYO Linux can't restrict behaviors by restricting
>   the argv[0]. But TOMOYO Linux doesn't attempt to restrict all argv[] elements
>   passed to execve(), because doing so will make the system too inconvenient
>   and frustrating to use.
> 
> Give different set of permissions to the same application.
> 
>   There are some non-executable applications (e.g. Java's class files).
>   Such applications use the same program for executing (e.g. Java Runtime
>   Environment). Since TOMOYO Linux has PIH, you can give different set of
>   permissions for each application by separating PIH for each application.
> 
>   Although TOMOYO Linux can switch context for every execve() requests,
>   it is preferable to be able to switch context without invoking execve().
>   So far, we are not providing APIs to switch context like AppArmor's
>   change_hat()/change_profile(). We'd like to introduce APIs to switch context
>   when distributors get ready to support TOMOYO Linux (in other words, after
>   TOMOYO Linux is merged into mainline).
> 
> Provide DMZ for remote logins.
> 
>   Recently, password brute-force attacks against SSH service are increasing.
>   But TOMOYO Linux's PIH can provide a room for deploying DMZ.
> 
>   Why password or public-key authentication is possible for only once?
>   Why not give normal users a chance to beat back attackers who logged in
>   through brute-force attacks?
> 
>   You can deploy extra login authentications that the only normal user knows
>   how to pass.
> 
> Provide simple RBAC-like administrative task division.
> 
>   TOMOYO Linux's PIH forms a tree structure.
>   This means that you can split one tree into several subtrees
>   and associate each subtree with each administrative task.
>   You can give each subtree necessary and sufficient permissions
>   for each administrative task.
> 
>   You can deploy custom authentication at the entry point of each subtree
>   so that one administrator cannot proceed to other administrator's subtrees.
> 
> And more...
> 
>   Your imagination invents new usage.
> 
> 
> Authors:
>   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
>   Toshiharu Harada <haradats@...data.co.jp>
>   Kentaro Takeda <takedakn@...data.co.jp>
> 
> 
> Appendix 1 - Usability features of TOMOYO Linux
> 
> TOMOYO Linux switches the context of a process whenever a process executes
> a program, but there are two exceptions.
> Administrator may relocate domain of a process if PIH is not meaningful for
> that process (e.g. daemon programs). This exception allows administrator
> restart daemon programs.
> Administrator may suppress domain transition if domain transition is not
> meaningful for that process (e.g. /bin/touch called from /etc/init.d/ scripts).
> This exception reduces memory usage for policy.
> 
> TOMOYO Linux can apply access control over all userspace applications,
> but administrator can also apply access control over only specific userspace
> applications if he/she wishes so.
> 
> TOMOYO Linux supports "delayed enforcing mode" that allows administrator
> interactively judge whether a request which is not defined in the policy
> should be permitted or rejected.
> This mode helps administrator adjust the policy after software updates.
> 
> 
> Appendix 2 - Presentation slides
> 
> - PacSec2007: TOMOYO Linux: "A Practical Method to Understand and Protect
>                              Your Own Linux Box"
>   http://sourceforge.jp/projects/tomoyo/document/PacSec2007-en-demo.pdf
> 
> - OLS2007: "TOMOYO Linux BoF"
>   http://sourceforge.jp/projects/tomoyo/document/ols2007-tomoyo-20070629.pdf
> 
> - ELC2007: "TOMOYO Linux - A Lightweight and Manageable Security System
>             for PC and Embedded Linux"
>   http://sourceforge.jp/projects/tomoyo/document/elc2007-presentation-20070418-for_linux.pdf 
> -
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