NAME
krb5_425_conv_principal,
krb5_425_conv_principal_ext,
krb5_524_conv_principal —
converts to
and from version 4 principals
LIBRARY
Kerberos 5 Library (libkrb5, -lkrb5)
SYNOPSIS
#include <krb5/krb5.h>
krb5_error_code
krb5_425_conv_principal(
krb5_context
context,
const char
*name,
const char
*instance,
const char
*realm,
krb5_principal
*principal);
krb5_error_code
krb5_425_conv_principal_ext(
krb5_context
context,
const char
*name,
const char
*instance,
const char
*realm,
krb5_boolean
(*func)(krb5_context, krb5_principal),
krb5_boolean resolve,
krb5_principal *principal);
krb5_error_code
krb5_524_conv_principal(
krb5_context
context,
const
krb5_principal principal,
char *name,
char *instance,
char *realm);
DESCRIPTION
Converting between version 4 and version 5 principals can at best be described
as a mess.
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
name,
instance, and
realm, to a version
5 principal. This can result in several possible principals, and if
func is non-NULL, it will be called for each candidate
principal.
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
func). If the
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
func, and the value of
v4_instance_resolve
(from the
libdefaults
section) as
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
name,
instance, and
realm should be at least 40 characters long.
EXAMPLES
Since this is confusing an example is in place.
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:
foo.com
a-host.foo.com
b-host.bar.com
the following conversions will be made:
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.
SEE ALSO
krb5_build_principal(3),
krb5_free_principal(3),
krb5_parse_name(3),
krb5_sname_to_principal(3),
krb5_unparse_name(3),
krb5.conf(5)