netdev - Re: ipv6_addr_type() and mapped IPv4 loopback

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Date:	Tue, 4 Nov 2008 11:44:59 -0500
From:	Chuck Lever <chuck.lever@...cle.com>
To:	Brian Haley <brian.haley@...com>
Cc:	netdev@...r.kernel.org
Subject: Re: ipv6_addr_type() and mapped IPv4 loopback

Hi Brian-

On Nov 3, 2008, at Nov 3, 2008, 9:33 PM, Brian Haley wrote:
> Chuck Lever wrote:
>> The __ipv6_addr_type() function does not recognize the mapped IPv4  
>> loopback address:
>>   ::ffff:7f00:0001
>> as type IPV6_ADDR_LOOPBACK.  Is this intentional?
>
> I would think that since the IPv6 loopback address is ::1, and ipv4- 
> mapped is ::ffff:* that this would be IPV6_ADDR_MAPPED.  That's what  
> RFC 4291 seems to say.

So the answer to my original question is then "yes, this is  
intentional," correct?

On a system with an AF_INET6 listener, legacy applications use  
127.0.0.1 to contact a local listener.  The incoming source address  
will be ::ffff:7f00:0001, not ::1.  This means IPv6-enabled  
applications have to perform a separate check for ::ffff:7f00:0001 if  
they are looking for loopback addresses.

The kernel's lockd must verify that an NLM request comes from the  
local user space.  It's not a lot of extra logic, but it is a subtlety.

-- 
Chuck Lever
chuck[dot]lever[at]oracle[dot]com
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