Re: Comments on draft-freed-sieve-environment-04

[Ned Freed <[e-mail]>]

> If the SMTP session was over IPv6, what should the "remote-ip" environment
> item be set to?

I would think that in this case it would obviously be the IPv6 address.
However, I take your point that the format of such addresses needs to be
specified - the underlying standards for address formats having failed to
specify this with sufficient clarity or generality, it is now up to every
application protocol where such addresses appear to deal with it separately.
Sigh. Not the way it should be, but how it is.

  Perhaps there should be a prefix on the value that
> indicates the address family, or it should be formatted like the 'host'
> part of URI?

> Note that the obvious test of
>  	environment :matches "remote-ip" "*.*.*.*"

> will match an IPv6 address literal if the implementation uses the
>  	x:x:x:x:x:x:d.d.d.d
> form, such as with the IPv4 compat addresses, ala "::FFFF:1.2.3.4".

> (Yes, this thought was triggered by the "IPv6-only" experiment during the
> IETF technical plenary.)

Well, I certainly hope that for any given address there's exactly one way it
will end up being represented. If that's not the case then there's a major
problem that goes far beyond this specific issue.

There's also the issue of how any future sort of address should be handled.
Since RFC 2821 has already had to deal with this I think the best way to handle
it is by referring to the formats defined there. I currently have:

 "remote-ip"
           => IP address of remote SMTP/LMTP/Submission client, if
              applicable and available. IPv4, IPv6, and other types of
              addresses are respectively represented in the formats
              defined by the IPv4-address-literal, IPv6-address-literal,
              and General-address-literal productions defined in
              [RFC 2821] section 4.1.3.

> There probably should be a security consideration that explains that the
> value of the "remote-host" item may be controlled by an untrusted source.
> For example, the test
>  	environment :matches "remote-host" "*.mydomain.com"

> is *not* a good way to test whether the message came from 'outside' unless
> the implementation there's some sort of IP->host->IP consistency check
> made.

Also a good point. I have added:

  The remote-host environment item defined in this specification is usually
  determined by performing a PTR DNS lookup on the client IP address. This
  information may come from an untrusted source. For example, the test:

    if environment :matches "remote-host" "*.mydomain.com" { ... }

  is not a good way to test whether the message came from 'outside' becaus
  anyone who can create a PTR record can create one that refers to whatever
  domain they choose.

> (The sendmail MTA faced the above issues some time ago for the pre-defined
> variables it provides to its rulesets.  To quote the sendmail operations
> guide, it defined variables as follows:
>        ${client_addr}
>             The  IP  address  of  the  SMTP   client.    IPv6
>             addresses  are  tagged  with  "IPv6:"  before the
>             address.  Defined in the SMTP server only.

>        ${client_name}
>             The host name of the SMTP client.   This  may  be
>             the  client's  bracketed IP address in the form [
>             nnn.nnn.nnn.nnn    ]    for    IPv4     and     [
>             IPv6:nnnn:...:nnnn  ] for IPv6 if the client's IP
>             address is not resolvable, or if it is resolvable
>             but  the  IP  address  of  the  resolved hostname
>             doesn't match the original IP  address.   Defined
>             in    the    SMTP    server   only.    See   also
>             ${client_resolve}.

I think a simpler way to handle this is to say that the name will
be blank if it cannot be resolved into a host name. How about:

 "remote-host"
           => Host name of remote SMTP/LMTP/Submission client, if
              applicable and available. The empty string will be returned
              if for some reason this information cannot be obtained for
              the current client.


>        ${client_ptr}
>             The  result  of  the PTR lookup for the client IP
>             address.    Note:   this   is   the    same    as
>             ${client_name}  if  and only if ${client_resolve}
>             is OK.  Defined in the SMTP server only.

>        ${client_resolve}
>             Holds  the  result  of  the  resolve   call   for
>             ${client_name}.  Possible values are:

>                 OK        resolved successfully
>                 FAIL      permanent lookup failure
>                 FORGED    forward lookup doesn't match reverse lookup
>                 TEMP      temporary lookup failure

>             Defined   in  the  SMTP  server  only.   sendmail
>             performs a hostname lookup on the IP  address  of
>             the  connecting client.  Next the IP addresses of
>             that hostname are looked up.  If  the  client  IP
>             address  does  not  appear in that list, then the
>             hostname is maybe forged.  This is  reflected  as
>             the  value  FORGED  for  ${client_resolve} and it
>             also shows up in $_ as "(may be forged)".

> While client_ptr and client_resolve are probably overkill for the sieve
> environment extension, the tagging in client_addr and precise definition
> of when client_name contains a name and not an address literal seem like
> practical guidance in this area.)

I agree - see above for my proposed solution for this issue.

				Ned