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krb5_425_conv_principal krb5_425_conv_principal_ext krb5_524_conv_principal - converts to and from version 4 principals
Kerberos 5 Library (libkrb5, -lkrb5)
A version 4 principal consists of a name, an instance, and a realm. A version 5 principal consists of one or more components, and a realm. In some cases also the first component/name will differ between version 4 and version 5. Furthermore the second component of a host principal will be the fully qualified domain name of the host in question, while the instance of a version 4 principal will only contain the first part (short hostname). Because of these problems the conversion between principals will have to be site customized.
krb5_425_conv_principal_ext ();
will try to convert a version 4 principal, given by
Fa name ,
Fa instance ,
and
Fa realm ,
to a version 5 principal. This can result in several possible
principals, and if
Fa func
is non-NULL, it will be called for each candidate principal.
Fa func
should return true if the principal was
``good''
To accomplish this,
krb5_425_conv_principal_ext ();
will look up the name in
krb5.conf
It first looks in the
v4_name_convert/host
subsection, which should contain a list of version 4 names whose
instance should be treated as a hostname. This list can be specified
for each realm (in the
realms
section), or in the
libdefaults
section. If the name is found the resulting name of the principal
will be the value of this binding. The instance is then first looked
up in
v4_instance_convert
for the specified realm. If found the resulting value will be used as
instance (this can be used for special cases), no further attempts
will be made to find a conversion if this fails (with
Fa func ) .
If the
Fa resolve
parameter is true, the instance will be looked up with
gethostbyname (.);
This can be a time consuming, error prone, and unsafe operation. Next
a list of hostnames will be created from the instance and the
v4_domains
variable, which should contain a list of possible domains for the
specific realm.
On the other hand, if the name is not found in a host section, it is looked up in a v4_name_convert/plain binding. If found here the name will be converted, but the instance will be untouched.
This list of default host-type conversions is compiled-in:
v4_name_convert = {
host = {
ftp = ftp
hprop = hprop
imap = imap
pop = pop
rcmd = host
smtp = smtp
}
}
It will only be used if there isn't an entry for these names in the config file, so you can override these defaults.
krb5_425_conv_principal ();
will call
krb5_425_conv_principal_ext ();
with
NULL
as
Fa func ,
and the value of
v4_instance_resolve
(from the
libdefaults
section) as
Fa resolve .
krb5_524_conv_principal ();
basically does the opposite of
krb5_425_conv_principal (,);
it just doesn't have to look up any names, but will instead truncate
instances found to belong to a host principal. The
Fa name ,
Fa instance ,
and
Fa realm
should be at least 40 characters long.
Assume that we have the ``foo.com'' and ``bar.com'' domains that have shared a single version 4 realm, FOO.COM. The version 4 krb.realms file looked like:
foo.com FOO.COM .foo.com FOO.COM .bar.com FOO.COM
A krb5.conf file that covers this case might look like:
[libdefaults]
v4_instance_resolve = yes
[realms]
FOO.COM = {
kdc = kerberos.foo.com
v4_instance_convert = {
foo = foo.com
}
v4_domains = foo.com
}
With this setup and the following host table:
the following conversions will be made:foo.com a-host.foo.com b-host.bar.com
rcmd.a-host -> host/a-host.foo.com ftp.b-host -> ftp/b-host.bar.com pop.foo -> pop/foo.com ftp.other -> ftp/other.foo.com other.a-host -> other/a-host
The first three are what you expect. If you remove the ``v4_domains'' the fourth entry will result in an error (since the host ``other'' can't be found). Even if ``a-host'' is a valid host name, the last entry will not be converted, since the ``other'' name is not known to represent a host-type principal. If you turn off ``v4_instance_resolve'' the second example will result in ``ftp/b-host.foo.com'' (because of the default domain). And all of this is of course only valid if you have working name resolving.
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