[ldns-users] oxffffffff in dns records cause a syntax error in ldns-read-zone

[W.C.A. Wijngaards]

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Hi,

On 01/11/2011 08:31 PM, Robert Edmonds wrote:
> Miek Gieben wrote:
>>  287         len = strlen((char*)str);
>>  288         /* octet representation can make strings a lot longer than actual length */
>>  289         if (len > LDNS_MAX_DOMAINLEN * 4) {
>>  290                 return LDNS_STATUS_DOMAINNAME_OVERFLOW;
>>  291         }
> 
> ldns/rr.h:#define LDNS_MAX_DOMAINLEN    255
> 
> 255 * 4 is 1020.
> 
> from libbind <arpa/nameser.h>,
> 
> #define NS_MAXDNAME     1025    /*%< maximum domain name (presentation format)*/
> 
> i don't recall off-hand the math to come up with the 1025 value...

I would argue that the ldns 4*255 is correct.  The max wireformat domain
name length including label-count-values and end-root-label is 255
(because 1034 says so and because that fits into a single octet).  Thus
its representation cannot be longer than 255 * '\123'.  Actually even a
little shorter since the final root label would be a '.' and thus not 4
characters in its representation, and other label-divisor dots would
also be short dots.  And since labels can be 63 characters at most and
then require a dot to terminate the label, it is actually again a couple
characters shorter.

So the longest representation domain name has few labels (because dots
are so short), 256/64 is 4 labels. Of the 255 octets on the wire, 4 are
label lengths and one is the end root label. leaving 251 octets that
need '\123' representation, for a maximum length of 251*4 + 5 = 1009.

Best regards,
   Wouter
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