linux-kernel - Re: [PATCH v5 00/21] EVM

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Message-ID: <30374.1306849210@turing-police.cc.vt.edu>
Date:	Tue, 31 May 2011 09:40:10 -0400
From:	Valdis.Kletnieks@...edu
To:	Mimi Zohar <zohar@...ux.vnet.ibm.com>
Cc:	Pavel Machek <pavel@....cz>,
	David Safford <safford@...son.ibm.com>,
	Casey Schaufler <casey@...aufler-ca.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-security-module@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	James Morris <jmorris@...ei.org>, Greg KH <greg@...ah.com>,
	Dmitry Kasatkin <dmitry.kasatkin@...ia.com>
Subject: Re: [PATCH v5 00/21] EVM

On Tue, 31 May 2011 08:05:08 EDT, Mimi Zohar said:

> For files that you don't expect to change, such as ELF executables, you
> probably could use the immutable flag, but using a digital signature
> provides authenticity as well, which the immutable flag does not
> provide.

The problem with 'chattr +i' is that if an attacker gets root, they can 'chattr
-i' and start scribbling. I've never personally trusted it for anything more
than protecting against overexuberant root processes that forget to obey file
permissions (like the DHCP script that keeps insisting on removing all the IPv6
nameservers out of my /etc/resolv.conf even when it's mode 444). As you noted,
digitally signing the executables with a key not found on the system raises the
bar substantially..


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