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

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Date:	Sun, 18 Jul 2010 10:33:10 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:	davem@...emloft.net, 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.

Le samedi 17 juillet 2010 à 10:17 +0900, Tetsuo Handa a écrit :
> David Miller wrote:
> > From: Tetsuo Handa
> > Date: Sat, 17 Jul 2010 01:14:38 +0900
> > 
> > > Below is a patch for post recvmsg() operation. I modified the patch to call
> > > skb_recv_datagram() again (for udp_recvmsg(), raw_recvmsg(), udpv6_recvmsg())
> > > if LSM dicided to drop the message. (Regarding rawv6_recvmsg(), I didn't do so
> > > in accordance with the comment at "csum_copy_err:".)
> > > What do you think about this verion?
> > 
> > This looks fine, but regardless of that comment I think the IPV6 raw recvmsg()
> > should loop just as the IPV4 one does in your patch.
> > 
> Thank you, David.
> I updated to call skb_recv_datagram() for rawv6_recvmsg() case too.
> 
> NETWORKING [IPv4/IPv6] maintainers and Paul, is below patch fine for you?
> 
> Regards.
> ----------------------------------------
> >From b43154a90bc7494ec1ee301e692d2bbf29c8f2f8 Mon Sep 17 00:00:00 2001
> From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> Date: Sat, 17 Jul 2010 09:52:38 +0900
> Subject: [PATCH] LSM: Add post recvmsg() hook.
> 
> Current pre recvmsg hook (i.e. security_socket_recvmsg()) has two problems.
> 
> One is that it will cause eating 100% of CPU time if the caller does not
> close() the socket when recvmsg() failed due to security_socket_recvmsg(), for
> subsequent select() notifies the caller of readiness for recvmsg() since the
> datagram which would have been already picked up if security_socket_recvmsg()
> did not return error is remaining in the queue.
> 
> The other is that it is racy if LSM module wants to do filtering based on
> "which process can pick up datagrams from which source" because the process
> which picks up the datagram is not known until skb_recv_datagram() and lock
> is not held between security_socket_recvmsg() and skb_recv_datagram().
> 
> This patch introduces post recvmsg hook (i.e. security_socket_post_recvmsg())
> in order to solve above problems at the cost of ability to pick up the datagram
> which would have been picked up if preceding security_socket_post_recvmsg() did
> not return error.
> 
> Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>

I read this patch and could not find out if an SNMP counter was
increased in the case a frame was not delivered but dropped in kernel
land.



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