linux-kernel - Re: ACLs

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Date:	Fri, 4 Aug 2006 19:34:02 -0400
From:	Kyle Moffett <mrmacman_g4@....com>
To:	RazorBlu <razorblu@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: ACLs

On Aug 04, 2006, at 18:52:41, RazorBlu wrote:
> Because instead of having an all-powerful account (which we so  
> lovingly know as root), you can separate specific roles to  
> different accounts. To use Windows' ACLs as an example:
>
> - Adjust memory quotas for a process
> - Allow/deny access to this computer from the network
> - Backup files and directories
> - Bypass traverse checking
> - Change system time
> - Increase scheduling priority
> - Load and unload device drivers
> - Manage auditing and security logs
> - Restore files and directories
> - Shutdown the system
> - Take ownership of files or other objects

This is _exactly_ what SELinux does for you.  You can break down  
permissions on very nearly a per-syscall basis (not quite, for  
efficiency reasons, but pretty damn close).

> As you can see, those are finely-grained controls. Why would these  
> be useful on Linux? Because you can have a root account which can  
> bind Apache to a port <1024, and even if it is compromised it  
> cannot "shutdown the system," or "deny access to this computer from  
> the network," thus the attacker will be able to cause minimal  
> damage. Yes, the same can be done on Linux using SELinux, AppArmor,  
> or some other ACL system, but again - those aren't part of the  
> kernel. They are extra apps, and adding layers is not always the  
> best solution when it comes to security.

You're quite wrong about SELinux; it _is_ part of the kernel.   
Admittedly it requires a policy to be built and loaded from  
userspace, but your "ACLs" would require some ACL utilities to apply  
those from userspace.  In any case SELinux is an extremely powerful  
model; you can define your arbitrary RBAC+TE state machine and  
constraints, then the kernel applies it to your system; as simple (or  
horribly complicated, as the case may be) as that.

> Um.. Forgive me for a second, but are you suggesting that a Linux  
> system running a service(s) under full root privileges (such as  
> Apache) is just as secure as a Linux system running the same  
> process but with compartmentalisation to make sure that each  
> service has access to just the files and directories it needs,  
> achieved (currently) via AppArmor, SELinux, or a similar ACL system?

Here's a better security model:  SELinux lets you give root access to  
everybody and still have a 100% secure system (although it's not  
really recommended).  Google around for the public SSH-accessible  
SELinux testbeds with root's password set to "password" or "1234" or  
whatever and feel free to log in and have a look.  Besides, we do  
have POSIX ACLs on files; if that's what you're looking for, but  
that's not extensible enough to cover processes too.

Cheers,
Kyle Moffett

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