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.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)