linux-kernel - Re: [TOMOYO #5 02/18] Add wrapper functions for VFShelperfunctions.

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Date:	Sat, 17 Nov 2007 13:04:02 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	trond.myklebust@....uio.no
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org
Subject: Re: [TOMOYO #5 02/18] Add wrapper functions for VFShelperfunctions.

Hello.

Trond Myklebust wrote:
> The problem is that you have thrown away the main tool for documenting
> the requirement, and for enforcing correctness (i.e. function argument
> checking by the compiler).
I'm sorry. I wanted to know whether the below approach is possible.

> The old functions are still there, are still exported, and still take
> the same arguments as before, but you have now added a hidden
> requirement that I have to set last_vfsmount when I call them. If I
> haven't read your patch, and just call one of those vfs_* functions as
> before, without setting last_vfsmount, I break your model, and I won't
> find out until someone reports an obscure bug at runtime.
I don't care if some kernel module calls vfs_* without setting last_vfsmount
because there is no reason to reject requests from kernel code.
Setting last_vfsmount is required for requests from userland process.
This approach makes it possible to
(1) tell whether the vfs_* calls are from userland or kernel
and
(2) leave kernel modules that are not called from userland unchanged.
This is why this patch doesn't and needn't to modify fs/*/ files.

Thanks.

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