netdev - Re: [PATCH] LSM: Add post recvmsg() hook.

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Message-Id: <201007230022.o6N0MKLt053955@www262.sakura.ne.jp>
Date:	Fri, 23 Jul 2010 09:22:20 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	davem@...emloft.net
Cc:	kuznet@....inr.ac.ru, pekkas@...core.fi, jmorris@...ei.org,
	yoshfuji@...ux-ipv6.org, kaber@...sh.net, paul.moore@...com,
	netdev@...r.kernel.org, linux-security-module@...r.kernel.org
Subject: Re: [PATCH] LSM: Add post recvmsg() hook.

David Miller wrote:
> The fact is going to remain that you will be unable to return data
> from recvmsg() to a blocking socket when ->poll() returns true even
> though data is in fact there in the socket receive queue.
> 
> This is something that the existing LSM hooks do not do.

This is something that the existing security_socket_recvmsg() hook does do.
SELinux is unable to return data from recvmsg() to a blocking socket when
->poll() returns true even though data is in fact there in the socket receive
queue.
We agreed below situation, didn't we?

Tetsuo Handa wrote:
> > > Excuse me, below check is made inside recvmsg() and may return error if
> > > SELinux's policy has changed after the select() said "ready" and before
> > > security_socket_recvmsg() is called. No?
> > 
> > It does this before pulling the packet out of the receive queue of the
> > socket.  It's like signalling a parameter error to the process, no
> > socket state is changed.
> 
> So, we agreed that security_socket_recvmsg() is allowed to return error code
> rather than available data even if both conditions
> 
> 1) Application makes poll() on UDP socket in blocking mode, and UDP
>    reports that receive data is available
> 
> and
> 
> 2) Application, after such a poll() call, makes a blocking recvmsg() call
>    and no other activity has occurred on the socket meanwhile
> 
> are met.
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