linux-kernel - Re: [Patch 3/3] net: reserve ports for applications using fixed port numbers

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Date:	Tue, 13 Apr 2010 15:13:24 +0800
From:	Cong Wang <amwang@...hat.com>
To:	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
CC:	opurdila@...acom.com, eric.dumazet@...il.com,
	netdev@...r.kernel.org, nhorman@...driver.com, davem@...emloft.net,
	ebiederm@...ssion.com, linux-kernel@...r.kernel.org
Subject: Re: [Patch 3/3] net: reserve ports for applications using fixed port
 numbers

Tetsuo Handa wrote:
> Hello.
> 
>> --- linux-2.6.orig/drivers/infiniband/core/cma.c
>> +++ linux-2.6/drivers/infiniband/core/cma.c
>> @@ -1980,6 +1980,8 @@ retry:
>>  	/* FIXME: add proper port randomization per like inet_csk_get_port */
>>  	do {
>>  		ret = idr_get_new_above(ps, bind_list, next_port, &port);
>> +		if (!ret && inet_is_reserved_local_port(port))
>> +			ret = -EAGAIN;
>>  	} while ((ret == -EAGAIN) && idr_pre_get(ps, GFP_KERNEL));
>>  
>>  	if (ret)
>>
> I think above part is wrong. Below program
...
> 
> This result suggests that above loop will continue until idr_pre_get() fails
> due to out of memory if all ports were reserved.
> 
> Also, if idr_get_new_above() returned 0, bind_list (which is a kmalloc()ed
> pointer) is already installed into a free slot (see comment on
> idr_get_new_above_int()). Thus, simply calling idr_get_new_above() again will
> install the same pointer into multiple slots. I guess it will malfunction later.

Thanks for testing!

How about:

+		if (!ret && inet_is_reserved_local_port(port))
+			ret = -EBUSY;

? So that it will break the loop and return error.
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