linux-kernel - Re: [TOMOYO #7 30/30] Hooks for SAKURA and TOMOYO.

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Date:	Tue, 15 Apr 2008 20:14:41 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	casey@...aufler-ca.com, sds@...ho.nsa.gov,
	crispin@...spincowan.com, casey@...aufler-ca.com
Cc:	serue@...ibm.com, matthew@....cx, paul.moore@...com,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org, takedakn@...data.co.jp,
	linux-fsdevel@...r.kernel.org
Subject: Re: [TOMOYO #7 30/30] Hooks for SAKURA and TOMOYO.

Casey Schaufler wrote:
> The question of protections on the object named /etc/passwd came
> up time and time again. The notion that /etc/passwd could be a
> symlink to /home/smalley/heeheehee really gave evaluators the
> whillies. As did the chroot environment, where /roots/crispin/etc/passwd
> could magicly become /etc/passwd.
Why do people continue speaking symlinks and chroots?
To avoid the effect of symlinks and chroots, AppArmor and TOMOYO Linux
derive pathnames from dentry and vfsmount.
If /etc/passwd was a symlink, the derived pathname will be /home/smalley/heeheehee.
If accessed from inside a chroot, the derived pathname will be /roots/crispin/etc/passwd.

It is true that namespace may differ between processes,
but I think that that is the matter of how to restrict namespace manipulation operations.
As I said, a system can't survive if namespace is madly manipulated.
To keep the system workable, /bin/ must be the directory for binary programs,
/etc/ must be the directory for configuration files, and so on in all namespaces.

It is true that the pathname may change while traversing up the dentry/vfsmount trees.
But the change does not occur infinitely.
As I said, a system can't survive if files and directories are madly renamed.
The possible changes are bounded by the policy.

At least, I want people not to speak symlinks and chroots when talking about
AppArmor and TOMOYO Linux.

Regards.
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