linux-kernel - Re: Problem with accessing namespace

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Date:	Thu, 8 Nov 2007 07:04:23 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	hch@...radead.org
Cc:	linux-security-module@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	crispin@...spincowan.com
Subject: Re: Problem with accessing namespace_sem from LSM.

Hello.

Christoph Hellwig wrote:
> > Isn't security_inode_create() a part of VFS internals?
> It's not.  security_inode_create is part of the LSM infrastructure, and
> the actual methods are part of security modules and definitively not
> VFS internals.
The reason why I want to access namespace_sem inside security_inode_create() is that
it doesn't receive "struct vfsmount" parameter.
If "struct vfsmount" *were* passed to security_inode_create(), 
I have no need to access namespace_sem.

And now, since calling down_read(&namespace_sem) causes deadlock, I'm looking for a solution.
What you said ("I'd start looking for design bugs in whatever code you have using it first.")
sounds "never try to implement pathname based access control at security_inode_create()",
which makes AppArmor (for OpenSuSE 10.1/10.2) and TOMOYO unable to apply access control.

At first, I thought that this lockdep's warning is a false positive,
since "struct inode" is allocated/freed dynamically.
But the warning still appears even after I disabled freeing memory
at destroy_inode() in fs/namei.c (so that address of locking object
in "struct inode" never be reused), it is likely genuine.

Regards.

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