linux-kernel - Re: [TOMOYO 15/15] LSM expansion for TOMOYO Linux.

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Message-Id: <200709032215.DCF36819.SLQtHFMFOOFOVJ@I-love.SAKURA.ne.jp>
Date:	Mon, 3 Sep 2007 22:15:27 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	paul.moore@...com
Cc:	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org, chrisw@...s-sol.org
Subject: Re: [TOMOYO 15/15] LSM expansion for TOMOYO Linux.

Hello.

Paul Moore wrote:
> I apologize for not recognizing your approach from our earlier discussion on 
> the LSM mailing list in July.  Unfortunately, I have the same objections to 
> these changes that I did back then and from what I can recall of the 
> discussion the rest of the kernel networking community agreed that these 
> changes are not the preferred way of solving this problem.  We offered 
> suggestions on how to accomplish your goals in a way that would be acceptable 
> upstream and I would encourage you to investigate those options further.

When I proposed a patch in July, I was patching at post-copy_to_user() step
(i.e. after sock_recvmsg()).
This approach messed up user-supplied buffer.

This time, I'm patching at pre-copy_to_user() step
(i.e. at skb_recv_datagram()).
This approach doesn't mess up user-supplied buffer.
I think this is a cleaner way than the previous patch.

Although read() gets an error when select() said "read ready",
I can't find other place to use for accomplishing my goals.

By the way, similar thing can happen when select() against
a file descriptor said "read ready" but read() gets an error
if security policy or security-id of the file has changed
between select() and read(), isn't it?
And such behavior is acceptable, isn't it?
If such behavior can happen and is acceptable and *preferable*,
I think checking permission at dequeue time (i.e. skb_recv_datagram())
is *preferable* way than checking permission at enqueue time
(i.e. socket_sock_rcv_skb()).

Regards.
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