linux-kernel - Re: [PATCH] Security: Implement and document RLIMIT

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Message-ID: <20090108005621.GI3164@didacte.laptop.org>
Date:	Wed, 7 Jan 2009 19:56:21 -0500
From:	Michael Stone <michael@...top.org>
To:	Evgeniy Polyakov <zbr@...emap.net>
Cc:	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH] Security: Implement and document RLIMIT_NETWORK.

On Thu, Jan 08, 2009 at 12:59:36AM +0300, Evgeniy Polyakov wrote:
>I meant that connected or accepted socket will not be able to send data
>via send() call, but will be able to receive data using recv().

A key fact which may not have stood out, since I didn't comment on it
explicitly in the code, is that the disqualification tests inserted by
the __sock_sendmsg() and unix_dgram_sendmsg hunks contain additional
conditions like

__sock_sendmsg():
+               && (msg->msg_name != NULL || msg->msg_namelen != 0))

unix_dgram_sendmsg():
+                       && !sunaddr->sun_path[0])

which return us to the usual codepaths whenever we're dealing with an
already-connected socket. Since my tests pass, can you post an example
of a failing send() call which you think should work?

>Your patch adds a rlimit check into __sock_sendmsg() call, which is
>invoked via usual send() path, but sendfile() and splice() are still
>exectuted without this check and thus will be able to send data after
>rlimit applied.

As far as I can tell, sendfile() and splice(), which operate solely on
fds, cannot be used to send messages via a disconnected socket.
Therefore, I /believe/ that they require no modification. Am I terribly
mistaken about this?

Thanks,

Michael
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