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

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Message-ID: <4B690681.6070908@redhat.com>
Date:	Wed, 03 Feb 2010 13:15:45 +0800
From:	Cong Wang <amwang@...hat.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	linux-kernel@...r.kernel.org, linux-rdma@...r.kernel.org,
	netdev@...r.kernel.org, Neil Horman <nhorman@...driver.com>,
	linux-sctp@...r.kernel.org, David Miller <davem@...emloft.net>
Subject: Re: [RFC Patch] net: reserve ports for applications using fixed port
 numbers

Eric Dumazet wrote:
> Le mardi 02 février 2010 à 23:30 -0500, Amerigo Wang a écrit :
>> This patch introduces /proc/sys/net/ipv4/ip_local_reserved_ports,
>> it can be used like ip_local_port_range, but this is used to
>> reserve ports for third-party applications which use fixed
>> port numbers within ip_local_port_range.
>>
>> This only affects the applications which call socket functions
>> like bind(2) with port number 0, to prevent the kernel getting the ports
>> within the specified range for them. For applications which use fixed
>> port number, it will have no effects.
>>
>> Any comments are welcome.
>>
>> Signed-off-by: WANG Cong <amwang@...hat.com>
>> Cc: David Miller <davem@...emloft.net>
>> Cc: Neil Horman <nhorman@...driver.com>
>> Cc: Eric Dumazet <eric.dumazet@...il.com>
> 
>>  		.procname	= "igmp_max_memberships",
>> diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
>> index f0126fd..83045ca 100644
>> --- a/net/ipv4/udp.c
>> +++ b/net/ipv4/udp.c
>> @@ -210,8 +210,11 @@ int udp_lib_get_port(struct sock *sk, unsigned short snum,
>>  		inet_get_local_port_range(&low, &high);
>>  		remaining = (high - low) + 1;
>>  
>> +again:
>>  		rand = net_random();
>>  		first = (((u64)rand * remaining) >> 32) + low;
>> +		if (inet_is_reserved_local_port(first))
>> +			goto again;
>>  		/*
>>  		 * force rand to be an odd multiple of UDP_HTABLE_SIZE
>>  		 */
> 
> Unless I misread the patch, you are checking only the 'first' port that
> udp_lib_get_port() chose.
> 
> I would use inet_get_local_reserved_ports(&min_res, &max_res);
> and check every port that we chose in the loop to avoid it if necessary.
> 

Hmm, right, 'first' is used to do iteration, but I did missed 'last'.
Thanks! I will fix this in the next update.

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