netdev - Re: [RFC Patch] net: reserve ports for applications using fixed port numbers

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Date:	Fri, 05 Feb 2010 14:01:43 +0800
From:	Cong Wang <amwang@...hat.com>
To:	Octavian Purdila <opurdila@...acom.com>
CC:	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	davem@...emloft.net, linux-kernel@...r.kernel.org,
	eric.dumazet@...il.com, linux-rdma@...r.kernel.org,
	netdev@...r.kernel.org, nhorman@...driver.com,
	linux-sctp@...r.kernel.org
Subject: Re: [RFC Patch] net: reserve ports for applications using fixed port
 numbers

Octavian Purdila wrote:
> On Friday 05 February 2010 02:41:12 you wrote:
>> David Miller wrote:
>>>> Octavian Purdila wrote:
>>>>> int inet_is_reserved_local_port(int port)
>>>>> {
>>>>> 	if (test_bit(port, reserved_ports))
>>>>> 		return 1;
>>>>> 	return 0;
>>>>> }
>>>> Above check is exactly what I'm doing in the LSM hook.
>>> But his version can be done inline in 2 or 3 instructions.
>>>
>>> An LSM hook will result in an indirect function call,
>>> all live registers spilled to the stack, then all of
>>> those reloaded when the function returns.
>>>
>>> It will be much more expensive.
>> If you can accept his version, I want to use his version (with an interface
>>  for updating above "reserved_ports" by not only root user's sysctl() but
>>  also MAC's policy configuration).
>>
> 
> I think that simply using an interface to update the reserved_ports from MAC 
> policy configuration module wouldn't work, as root will be able to modify the 
> policy via sysctl.
> 
> I think that we might need to:
> 
> a) have a reserved_port updater
> 
> b) put a LSM hook into that
> 
> c) use the reserved_port updater from sysctl
> 
> 

Ideally, you'd provide an interface for port allocator to use, so
doing port reservation will be easier.

Thanks.


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