linux-kernel - Re: r-o bind in nfsd

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Message-Id: <200803252045.CGB04105.HLSQFOJMtOFVOF@I-love.SAKURA.ne.jp>
Date:	Tue, 25 Mar 2008 20:45:53 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	neilb@...e.de, miklos@...redi.hu
Cc:	viro@...IV.linux.org.uk, haveblue@...ibm.com,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, hch@...radead.org,
	linux-security-module@...r.kernel.org, jmorris@...ei.org
Subject: Re: r-o bind in nfsd

Hello.

> Maybe some enhancement to the 'intent' structure with a similar
> effect could be done instead.
> 
> Then you could, presumably, put a security hook somewhere in
> link_path_walk for those modules (like AppArmor) which want to do
> checks based on the namespace.

I think link_path_walk() is not a good place to insert new LSM hooks
for pathname based access control (AppArmor and TOMOYO) purpose because

  (1) The kernel don't know what operation (open/create/truncate etc.) will be
      done at the moment of link_path_walk().

  (2) Not all operations call link_path_walk() before these operations
      are done. For example, ftruncate() doesn't call link_path_walk().

  (3) The rename() and link() operations handle two pathnames.
      But, it is not possible to know both pathnames at the moment of
      link_path_walk().

I think we need to introduce new LSM hooks outside link_path_walk().
http://kerneltrap.org/mailarchive/linux-fsdevel/2008/2/17/882024
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