On 10.3.2015 18:36, Simo Sorce wrote: > On Tue, 2015-03-10 at 18:26 +0100, Petr Spacek wrote: >> On 10.3.2015 17:35, Simo Sorce wrote: >>> On Tue, 2015-03-10 at 16:19 +0100, Petr Spacek wrote: >>>> On 10.3.2015 15:53, Simo Sorce wrote: >>>>> On Tue, 2015-03-10 at 15:32 +0100, Petr Spacek wrote: >>>>>> Hello, >>>>>> >>>>>> I would like to discuss Generic support for unknown DNS RR types (RFC >>>>>> 3597 >>>>>> [0]). Here is the proposal: >>>>>> >>>>>> LDAP schema >>>>>> =========== >>>>>> - 1 new attribute: >>>>>> ( <OID> NAME 'GenericRecord' DESC 'unknown DNS record, RFC 3597' EQUALITY >>>>>> caseIgnoreIA5Match SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 ) >>>>>> >>>>>> The attribute should be added to existing idnsRecord object class as MAY. >>>>>> >>>>>> This new attribute should contain data encoded according to RFC 3597 >>>>>> section >>>>>> 5 [5]: >>>>>> >>>>>> The RDATA section of an RR of unknown type is represented as a >>>>>> sequence of white space separated words as follows: >>>>>> >>>>>> The special token \# (a backslash immediately followed by a hash >>>>>> sign), which identifies the RDATA as having the generic encoding >>>>>> defined herein rather than a traditional type-specific encoding. >>>>>> >>>>>> An unsigned decimal integer specifying the RDATA length in octets. >>>>>> >>>>>> Zero or more words of hexadecimal data encoding the actual RDATA >>>>>> field, each containing an even number of hexadecimal digits. >>>>>> >>>>>> If the RDATA is of zero length, the text representation contains only >>>>>> the \# token and the single zero representing the length. >>>>>> >>>>>> Examples from RFC: >>>>>> a.example. CLASS32 TYPE731 \# 6 abcd ( >>>>>> ef 01 23 45 ) >>>>>> b.example. HS TYPE62347 \# 0 >>>>>> e.example. IN A \# 4 0A000001 >>>>>> e.example. CLASS1 TYPE1 10.0.0.2 >>>>>> >>>>>> >>>>>> Open questions about LDAP format >>>>>> ================================ >>>>>> Should we include "\#" constant? We know that the attribute contains >>>>>> record in >>>>>> RFC 3597 syntax so it is not strictly necessary. >>>>>> >>>>>> I think it would be better to follow RFC 3597 format. It allows blind >>>>>> copy&pasting from other tools, including direct calls to python-dns. >>>>>> >>>>>> It also eases writing conversion tools between DNS and LDAP format >>>>>> because >>>>>> they do not need to change record values. >>>>>> >>>>>> >>>>>> Another question is if we should explicitly include length of data >>>>>> represented >>>>>> in hexadecimal notation as a decimal number. I'm very strongly inclined >>>>>> to let >>>>>> it there because it is very good sanity check and again, it allows us to >>>>>> re-use existing tools including parsers. >>>>>> >>>>>> I will ask Uninett.no for standardization after we sort this out (they >>>>>> own the >>>>>> OID arc we use for DNS records). >>>>>> >>>>>> >>>>>> Attribute usage >>>>>> =============== >>>>>> Every DNS RR type has assigned a number [1] which is used on wire. RR >>>>>> types >>>>>> which are unknown to the server cannot be named by their mnemonic/type >>>>>> name >>>>>> because server would not be able to do name->number conversion and to >>>>>> generate >>>>>> DNS wire format. >>>>>> >>>>>> As a result, we have to encode the RR type number somehow. Let's use >>>>>> attribute >>>>>> sub-types. >>>>>> >>>>>> E.g. a record with type 65280 and hex value 0A000001 will be represented >>>>>> as: >>>>>> GenericRecord;TYPE65280: \# 4 0A000001 >>>>>> >>>>>> >>>>>> CLI >>>>>> === >>>>>> $ ipa dnsrecord-add zone.example owner \ >>>>>> --generic-type=65280 --generic-data='\# 4 0A000001' >>>>>> >>>>>> $ ipa dnsrecord-show zone.example owner >>>>>> Record name: owner >>>>>> TYPE65280 Record: \# 4 0A000001 >>>>>> >>>>>> >>>>>> ACK? :-) >>>>> >>>>> Almost. >>>>> We should refrain from using subtypes when not necessary, and in this >>>>> case it is not necessary. >>>>> >>>>> Use: >>>>> GenericRecord: 65280 \# 4 0A000001 >>>> >>>> I was considering that too but I can see two main drawbacks: >>>> >>>> 1) It does not work very well with DS ACI (targetattrfilter, anyone?). >>>> Adding >>>> generic write access to GenericRecord == ability to add TLSA records too, >>>> which you may not want. IMHO it is perfectly reasonable to limit write >>>> access >>>> to certain types (e.g. to one from private range). >>>> >>>> 2) We would need a separate substring index for emulating filters like >>>> (type==65280). AFAIK GenericRecord;TYPE65280 should work with presence >>>> index >>>> which will be handy one day when we decide to handle upgrades like >>>> GenericRecord;TYPE256->UriRecord. >>>> >>>> Another (less important) annoyance is that conversion tools would have to >>>> mangle record data instead of just converting attribute name->record type. >>>> >>>> >>>> I can be convinced that subtypes are not necessary but I do not see clear >>>> advantage of avoiding them. What is the problem with subtypes? >>> >>> Poor support by most clients, so it is generally discouraged. >> Hmm, it does not sound like a thing we should care in this case. DNS tree is >> not meant for direct consumption by LDAP clients (compare with cn=compat). >> >> IMHO the only two clients we should care are FreeIPA framework and >> bind-dyndb-ldap so I do not see this as a problem, really. If someone wants >> to >> access DNS tree by hand - sure, use a standard compliant client! >> >> Working ACI and LDAP filters sounds like good price for supporting only >> standards compliant clients. >> >> AFAIK OpenLDAP works well and I suspect that ApacheDS will work too because >> Eclipse has nice support for sub-types built-in. If I can draw some >> conclusions from that, sub-types are not a thing aliens forgot here when >> leaving Earth one million years ago :-) >> >>> The problem with subtypes and ACIs though is that I think ACIs do not >>> care about the subtype unless you explicit mention them. >> IMHO that is exactly what I would like to see for GenericRecord. It allows us >> to write ACI which allows admins to add any GenericRecord and at the same >> time >> allows us to craft ACI which allows access only to GenericRecord;TYPE65280 >> for >> specific group/user. >> >>> So perhaps bind_dyndb_ldap should refuse to use a generic type that >>> shadows DNSSEC relevant records ? >> Sorry, this cannot possibly work because it depends on up-to-date blacklist. >> >> How would the plugin released in 2015 know that highly sensitive OPENPGPKEY >> type will be standardized in 2016 and assigned number XYZ? > > Ok, show me an example ACI that works and you get my ack :)
Am I being punished for something? :-) Anyway, this monstrosity: (targetattr = "objectclass || txtRecord;test")(target = "ldap:///idnsname=*,cn=dns,dc=ipa,dc=example")(version 3.0;acl "permission:luser: Read DNS Entries";allow (compare,read,search) userdn = "ldap:///uid=luser,cn=users,cn=accounts,dc=ipa,dc=example";) Gives 'luser' read access only to txtRecord;test and *not* to the whole txtRecord in general. $ kinit luser $ ldapsearch -Y GSSAPI -s base -b 'idnsname=txt,idnsname=ipa.example.,cn=dns,dc=ipa,dc=example' SASL username: luser@IPA.EXAMPLE # txt, ipa.example., dns, ipa.example dn: idnsname=txt,idnsname=ipa.example.,cn=dns,dc=ipa,dc=example objectClass: top objectClass: idnsrecord tXTRecord;test: Guess what is new here! Filter '(tXTRecord;test=*)' works as expected and returns only objects with subtype ;test. The only weird thing I noticed is that search filter '(tXTRecord=*)' does not return the object if you have access only to an subtype with existing value but not to the 'vanilla' attribute. Maybe it is a bug? I will think about it for a while and possibly open a ticket. Anyway, this is not something we need for implementation. For completeness: $ kinit admin $ ldapsearch -Y GSSAPI -s base -b 'idnsname=txt,idnsname=ipa.example.,cn=dns,dc=ipa,dc=example' SASL username: admin@IPA.EXAMPLE # txt, ipa.example., dns, ipa.example dn: idnsname=txt,idnsname=ipa.example.,cn=dns,dc=ipa,dc=example objectClass: top objectClass: idnsrecord tXTRecord: nothing tXTRecord: something idnsName: txt tXTRecord;test: Guess what is new here! And yes, you assume correctly that (targetattr = "txtRecord") gives access to whole txtRecord including all its subtypes. ACK? :-) -- Petr^2 Spacek -- Manage your subscription for the Freeipa-devel mailing list: https://www.redhat.com/mailman/listinfo/freeipa-devel Contribute to FreeIPA: http://www.freeipa.org/page/Contribute/Code