Re: [PATCH] Update getaddrinfo to RFC 6724 (bug 29496)

[Andreas Schwab <schwab@suse.de>]

On Sep 04 2023, Florian Weimer wrote:

>> @@ -1653,7 +1667,7 @@ rfc3484_sort (const void *p1, const void *p2, void *arg)
>>  	  in_addr_t netmask2 = 0xffffffffu << (32 - a2->prefixlen);
>>  
>>  	  if ((in2_src_addr & netmask2) == (in2_dst_addr & netmask2))
>> -	    bit2 = fls (in2_dst_addr ^ in2_src_addr);
>> +	    bit2 = a2->prefixlen;
>>  	}
>
> This is an undocumented change that I can't find in RFC 6724.

See Appendix B, changes to the rules, "Changed the definition of
CommonPrefixLen()".

>
>>        else if (a1->dest_addr->ai_family == PF_INET6)
>>  	{
>> @@ -1672,18 +1686,33 @@ rfc3484_sort (const void *p1, const void *p2, void *arg)
>>  
>>  	  int i;
>>  	  for (i = 0; i < 4; ++i)
>>  	    {
>> +	      uint32_t mask1, mask2;
>> +	      if (i * 32 >= a1->prefixlen)
>> +		mask1 = 0;
>> +	      else if ((i + 1) * 32 > a1->prefixlen)
>> +		mask1 = 0xffffffffu << (32 - (a1->prefixlen & 31));
>> +	      else
>> +		mask1 = 0xffffffffu;
>> +	      if (i * 32 >= a2->prefixlen)
>> +		mask2 = 0;
>> +	      else if ((i + 1) * 32 > a2->prefixlen)
>> +		mask2 = 0xffffffffu << (32 - (a2->prefixlen & 31));
>> +	      else
>> +		mask2 = 0xffffffffu;
>> +	      if (((in1_dst->sin6_addr.s6_addr32[i]
>> +		    ^ in1_src->sin6_addr.s6_addr32[i]) & htonl (mask1)) != 0
>> +		  || ((in2_dst->sin6_addr.s6_addr32[i]
>> +		       ^ in2_src->sin6_addr.s6_addr32[i]) & htonl (mask2)) != 0)
>> +		{
>> +		  bit1 = fls (ntohl (in1_dst->sin6_addr.s6_addr32[i]
>> +				     ^ in1_src->sin6_addr.s6_addr32[i])
>> +			      & mask1);
>> +		  bit2 = fls (ntohl (in2_dst->sin6_addr.s6_addr32[i]
>> +				     ^ in2_src->sin6_addr.s6_addr32[i])
>> +			      & mask2);
>> +		  break;
>> +		}
>
> Why use the common prefix length for IPv6 addresses?  RFC 6724 pretends
> that IPv6 assignment is strictly hierarchical, but in reality, it's
> not.  Shouldn't we do the same thing as for IPv4 addresses?

That's the same consequence as above due to the changes in
CommonPrefixLen.

-- 
Andreas Schwab, SUSE Labs, schwab@suse.de
GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE  1748 E4D4 88E3 0EEA B9D7
"And now for something completely different."