INTERNET-DRAFT Stephen X. Nahm
June 16, 1996 Sun Microsystems
Binding Protocols for ONC RPC Version 2
draft-ietf-oncrpc-rpcbind-00.txt
ABSTRACT
This document describes the binding protocols used in conjunction with the
ONC Remote Procedure Call (ONC RPC Version 2) protocols.
STATUS OF THIS MEMO
This document is an Internet-Draft. Internet-Drafts are working documents
of the Internet Engineering Task Force (IETF), its areas, and its working
groups. Note that other groups may also distribute working documents as
Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months.
This Internet-Draft expires on December 16, 1996. Internet-Drafts may be
updated, replaced, or obsoleted by other documents at any time. It is not
appropriate to use Internet-Drafts as reference material or to cite them
other than as "work in progress."
To learn the current status of any Internet-Draft, please check the
"1id-abstracts.txt" listing contained in the Internet-Drafts Shadow
Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe), munnari.oz.au
(Pacific Rim), ds.internic.net (US East Coast), or ftp.isi.edu (US West Coast).
Distribution of this memo is unlimited.
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CONTENTS
1. Introduction
2. RPCBIND Program Protocol
2.1 RPCBIND Protocol Specification (in RPC Language)
2.2 RPCBIND Operation
2.2.1 RPCBIND Version 3
2.2.2 RPCBIND, Version 4
3. Port Mapper Program Protocol
3.1 Port Mapper Protocol Specification (in RPC Language)
3.2 Port Mapper Operation
4. Security Considerations
5. References
6. AUTHOR'S ADDRESS
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1. Introduction
This document specifies the binding protocols used in conjunction with ONC
RPC Version 2. As a prerequisite, the reader is expected to be familiar
with [1] and [2] which describe the ONC RPC Version 2 and XDR (External
Data Representation) protocols.
An RPC service is identified by its RPC program number, version number, and
the transport address where it may be reached. The transport address, in
turn, consists of a network address and a transport selector. In the case
of a service available over TCP/IP or UDP/IP, the network address will be
an IP address, and the transport selector will be a TCP or UDP port number.
A client program needs to know the RPC program number, version number, and
the transport address corresponding to a service in order to utilize the
service. Of these, the RPC program number and version number are usually
built into the client program, as part of the service definition. The
network address component of the transport address is usually available in
a name service, or is given as a parameter to the client program. The
transport selector (ie., the TCP or UDP port) is usually determined
dynamically, and varies with each invocation of the service. Server
programs allocate a transport address, and register it with a well-known
lookup service (well-known because it uses a fixed transport selector, and
resides at the same network address as the server). Client programs
consult the lookup service in order to obtain the server's transport
address.
Such a lookup service is very desirable because the range of well-known
transport selectors is very small for some transports and the number of
services is potentially very large. By running only the lookup service on
a well-known transport selector, the transport addresses of other remote
programs can be ascertained by querying the lookup service.
This document describes three versions of a lookup service, all of which
use the same RPC program number (100000, decimal). They all use port 111
over TCP and UDP transports. Versions 3 and 4 are described in Section 2
("RPCBIND Program Protocol"). Version 2 is described in Section 3 ("Port
Mapper Program Protocol").
The distinguishing characteristic of RPCBIND (versions 3 and 4) is that
this protocol uses a transport-independent format for the transport
address, known as the universal address format. An address in universal
address format is an ASCII string representation of the transport dependent
address. For example, the universal address format for a TCP/IP transport
address is the dotted-decimal representation [3] of the address extended
with the port number. If the IP address is "192.0.0.1" and the port number
is "111", then the universal address is "192.0.0.1.0.111".
String representation of addresses corresponding to a transport are defined
by the addressing authority for the transport. The RPCBIND protocol can be
used for binding ONC RPC clients and servers over any transport.
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The Port Mapper (version 2), on the other hand, is an older protocol that
is specific to TCP and UDP. It handles TCP and UDP ports directly.
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2. RPCBIND Program Protocol
The RPCBIND program maps RPC program and version numbers to universal
addresses, thus making dynamic binding of remote programs possible.
The RPCBIND program is bound to a well-known address of each supported
transport, and other programs register their dynamically allocated
transport address with it. The RPCBIND program then makes those addresses
publicly available.
The RPCBIND program also aids in broadcast RPC. A given RPC program will
usually have different transport address bindings on different machines, so
there is no way to directly broadcast to all of these programs. The RPCBIND
program, however, does have a well-known address. So, to broadcast to a
given program, the client actually sends its message to the RPCBIND program
located at the broadcast address. Each instance of the RPCBIND program that
picks up the broadcast then calls the local service specified by the
client. When the RPCBIND program gets the reply from the local service, it
sends the reply back to the client.
2.1 RPCBIND Protocol Specification (in RPC Language)
/*
* rpcb_prot.x
* rpcbind protocol, versions 3 and 4, in RPC Language
*/
/*
* rpcbind address for TCP/UDP
*/
const RPCB_PORT = 111;
/*
* A mapping of (program, version, network ID) to address
*
* The network identifier (r_netid):
* This is a string that represents a local identification for a network.
* This is defined by a system administrator based on local conventions,
* and cannot be depended on to have the same value on every system.
* The RPC program owner identifier (r_owner):
* This is a string that represents a user who "owns" the RPC program
* represented by the rpcb structure. This is usually the user who started
* the server that supplies this RPC program. rpcbind allows only the
* program owner to unregister the RPC program (some implementations also
* allow the user represented by the string "superuser" to unregister any
* RPC program).
*/
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struct rpcb {
unsigned int r_prog; /* program number */
unsigned int r_vers; /* version number */
string r_netid<>; /* network id */
string r_addr<>; /* universal address */
string r_owner<>; /* owner of this service */
};
struct rpcblist {
rpcb rpcb_map;
struct rpcblist *rpcb_next;
};
typedef rpcblist *rpcblist_ptr; /* results of RPCBPROC_DUMP */
/*
* Arguments of remote calls
*/
struct rpcb_rmtcallargs {
unsigned int prog; /* program number */
unsigned int vers; /* version number */
unsigned int proc; /* procedure number */
opaque args<>; /* argument */
};
/*
* Results of the remote call
*/
struct rpcb_rmtcallres {
string addr<>; /* remote universal address */
opaque results<>; /* result */
};
/*
* rpcb_entry contains a merged address of a service on a particular
* transport, plus associated netconfig information. A list of rpcb_entry
* items is returned by RPCBPROC_GETADDRLIST. The meanings and values used
* for the r_nc_* fields are given below.
*
* The network identifier (r_nc_netid):
* This is a string that represents a local identification for a network.
* This is defined by a system administrator based on local conventions,
* and cannot be depended on to have the same value on every system.
*
* Transport semantics (r_nc_semantics):
* This represents the type of transport, and has the following values:
* NC_TPI_CLTS (1) Connectionless
* NC_TPI_COTS (2) Connection oriented
* NC_TPI_COTS_ORD (3) Connection oriented with graceful close
* NC_TPI_RAW (4) Raw transport
*
* Protocol family (r_nc_protofmly):
* This identifies the family to which the protocol belongs. The
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* following values are defined:
* NC_NOPROTOFMLY "-"
* NC_LOOPBACK "loopback"
* NC_INET "inet"
* NC_IMPLINK "implink"
* NC_PUP "pup"
* NC_CHAOS "chaos"
* NC_NS "ns"
* NC_NBS "nbs"
* NC_ECMA "ecma"
* NC_DATAKIT "datakit"
* NC_CCITT "ccitt"
* NC_SNA "sna"
* NC_DECNET "decnet"
* NC_DLI "dli"
* NC_LAT "lat"
* NC_HYLINK "hylink"
* NC_APPLETALK "appletalk"
* NC_NIT "nit"
* NC_IEEE802 "ieee802"
* NC_OSI "osi"
* NC_X25 "x25"
* NC_OSINET "osinet"
* NC_GOSIP "gosip"
*
* Protocol name (r_nc_proto):
* This identifies a protocol within a family. The following are
* currently defined:
* NC_NOPROTO "-"
* NC_TCP "tcp"
* NC_UDP "udp"
* NC_ICMP "icmp"
*/
struct rpcb_entry {
string r_maddr<>; /* merged address of service */
string r_nc_netid<>; /* netid field */
unsigned int r_nc_semantics; /* semantics of transport */
string r_nc_protofmly<>; /* protocol family */
string r_nc_proto<>; /* protocol name */
};
/*
* A list of addresses supported by a service.
*/
struct rpcb_entry_list {
rpcb_entry rpcb_entry_map;
struct rpcb_entry_list *rpcb_entry_next;
};
typedef rpcb_entry_list *rpcb_entry_list_ptr;
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/*
* rpcbind statistics
*/
const rpcb_highproc_2 = RPCBPROC_CALLIT;
const rpcb_highproc_3 = RPCBPROC_TADDR2UADDR;
const rpcb_highproc_4 = RPCBPROC_GETSTAT;
const RPCBSTAT_HIGHPROC = 13; /* # of procs in rpcbind V4 plus one */
const RPCBVERS_STAT = 3; /* provide only for rpcbind V2, V3 and V4 */
const RPCBVERS_4_STAT = 2;
const RPCBVERS_3_STAT = 1;
const RPCBVERS_2_STAT = 0;
/* Link list of all the stats about getport and getaddr */
struct rpcbs_addrlist {
unsigned int prog;
unsigned int vers;
int success;
int failure;
string netid<>;
struct rpcbs_addrlist *next;
};
/* Link list of all the stats about rmtcall */
struct rpcbs_rmtcalllist {
unsigned int prog;
unsigned int vers;
unsigned int proc;
int success;
int failure;
int indirect; /* whether callit or indirect */
string netid<>;
struct rpcbs_rmtcalllist *next;
};
typedef int rpcbs_proc[RPCBSTAT_HIGHPROC];
typedef rpcbs_addrlist *rpcbs_addrlist_ptr;
typedef rpcbs_rmtcalllist *rpcbs_rmtcalllist_ptr;
struct rpcb_stat {
rpcbs_proc info;
int setinfo;
int unsetinfo;
rpcbs_addrlist_ptr addrinfo;
rpcbs_rmtcalllist_ptr rmtinfo;
};
/*
* One rpcb_stat structure is returned for each version of rpcbind
* being monitored.
*/
typedef rpcb_stat rpcb_stat_byvers[RPCBVERS_STAT];
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/*
* netbuf structure, used to store the transport specific form of
* a universal transport address.
*/
struct netbuf {
unsigned int maxlen;
opaque buf<>;
};
/*
* rpcbind procedures
*/
program RPCBPROG {
version RPCBVERS {
bool
RPCBPROC_SET(rpcb) = 1;
bool
RPCBPROC_UNSET(rpcb) = 2;
string
RPCBPROC_GETADDR(rpcb) = 3;
rpcblist_ptr
RPCBPROC_DUMP(void) = 4;
rpcb_rmtcallres
RPCBPROC_CALLIT(rpcb_rmtcallargs) = 5;
unsigned int
RPCBPROC_GETTIME(void) = 6;
netbuf
RPCBPROC_UADDR2TADDR(string) = 7;
string
RPCBPROC_TADDR2UADDR(netbuf) = 8;
} = 3;
version RPCBVERS4 {
bool
RPCBPROC_SET(rpcb) = 1;
bool
RPCBPROC_UNSET(rpcb) = 2;
string
RPCBPROC_GETADDR(rpcb) = 3;
rpcblist_ptr
RPCBPROC_DUMP(void) = 4;
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/*
* NOTE: RPCBPROC_BCAST has the same functionality as CALLIT;
* the new name is intended to indicate that this
* procedure should be used for broadcast RPC, and
* RPCBPROC_INDIRECT should be used for indirect calls.
*/
rpcb_rmtcallres
RPCBPROC_BCAST(rpcb_rmtcallargs) = RPCBPROC_CALLIT;
unsigned int
RPCBPROC_GETTIME(void) = 6;
netbuf
RPCBPROC_UADDR2TADDR(string) = 7;
string
RPCBPROC_TADDR2UADDR(netbuf) = 8;
string
RPCBPROC_GETVERSADDR(rpcb) = 9;
rpcb_rmtcallres
RPCBPROC_INDIRECT(rpcb_rmtcallargs) = 10;
rpcb_entry_list_ptr
RPCBPROC_GETADDRLIST(rpcb) = 11;
rpcb_stat_byvers
RPCBPROC_GETSTAT(void) = 12;
} = 4;
} = 100000;
2.2 RPCBIND Operation
RPCBIND is contacted by way of an assigned address specific to the
transport being used. For TCP/IP and UDP/IP, for example, it is port
number 111. Each transport has such an assigned, well-known address. The
following is a description of each of the procedures supported by RPCBIND.
2.2.1 RPCBIND Version 3
RPCBPROC_SET:
When a program first becomes available on a machine, it registers itself
with RPCBIND running on the same machine. The program passes its program
number "r_prog", version number "r_vers", network identifier "r_netid",
universal address "r_addr", and the owner of the service "r_owner". The
procedure returns a boolean response whose value is TRUE if the procedure
successfully established the mapping and FALSE otherwise. The procedure
refuses to establish a mapping if one already exists for the ordered set
("r_prog", "r_vers", "r_netid"). Note that neither "r_netid" nor "r_addr"
can be NULL, and that "r_netid" should be a valid network identifier on the
machine making the call.
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RPCBPROC_UNSET:
When a program becomes unavailable, it should unregister itself with the
RPCBIND program on the same machine. The parameters and results have
meanings identical to those of RPCBPROC_SET. The mapping of the ("r_prog",
"r_vers", "r_netid") tuple with "r_addr" is deleted. If "r_netid" is NULL,
all mappings specified by the ordered set ("r_prog", "r_vers", *) and the
corresponding universal addresses are deleted. Only the owner of the
service or the super-user is allowed to unset a service.
RPCBPROC_GETADDR:
Given a program number "r_prog", version number "r_vers", and network
identifier "r_netid", this procedure returns the universal address on
which the program is awaiting call requests. The "r_netid" field of the
argument is ignored and the "r_netid" is inferred from the network
identifier of the transport on which the request came in.
RPCBPROC_DUMP:
This procedure lists all entries in RPCBIND's database. The procedure
takes no parameters and returns a list of program, version, network
identifier, and universal addresses.
RPCBPROC_CALLIT:
This procedure allows a caller to call another remote procedure on the same
machine without knowing the remote procedure's universal address. It is
intended for supporting broadcasts to arbitrary remote programs via
RPCBIND's universal address. The parameters "prog", "vers", "proc", and
args are the program number, version number, procedure number, and
parameters of the remote procedure.
Note - This procedure only sends a response if the procedure was
successfully executed and is silent (no response) otherwise.
The procedure returns the remote program's universal address, and the
results of the remote procedure.
RPCBPROC_GETTIME:
This procedure returns the local time on its own machine in seconds since
the midnight of the First day of January, 1970.
RPCBPROC_UADDR2TADDR:
This procedure converts universal addresses to transport specific
addresses.
RPCBPROC_TADDR2UADDR:
This procedure converts transport specific addresses to universal
addresses.
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2.2.2 RPCBIND, Version 4
Version 4 of the RPCBIND protocol includes all of the above procedures, and
adds several additional ones.
RPCBPROC_BCAST:
This procedure is identical to the version 3 RPCBPROC_CALLIT procedure.
The new name indicates that the procedure should be used for broadcast RPCs
only. RPCBPROC_INDIRECT, defined below, should be used for indirect RPC
calls.
RPCBPROC_GETVERSADDR:
This procedure is similar to RPCBPROC_GETADDR. The difference is the
"r_vers" field of the rpcb structure can be used to specify the version of
interest. If that version is not registered, no address is returned.
RPCBPROC_INDIRECT:
Similar to RPCBPROC_CALLIT. Instead of being silent about errors (such as
the program not being registered on the system), this procedure returns an
indication of the error. This procedure should not be used for broadcast
RPC. It is intended to be used with indirect RPC calls only.
RPCBPROC_GETADDRLIST:
This procedure returns a list of addresses for the given rpcb entry. The
client may be able use the results to determine alternate transports that
it can use to communicate with the server.
RPCBPROC_GETSTAT:
This procedure returns statistics on the activity of the RPCBIND server.
The information lists the number and kind of requests the server has
received.
Note - All procedures except RPCBPROC_SET and RPCBPROC_UNSET can be called
by clients running on a machine other than a machine on which RPCBIND is
running. RPCBIND only accepts RPCBPROC_SET and RPCBPROC_UNSET requests by
clients running on the same machine as the RPCBIND program.
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3. Port Mapper Program Protocol
The port mapper program maps RPC program and version numbers to transport-
specific port numbers. This program makes dynamic binding of remote
programs possible. The port mapper protocol differs from the newer RPCBIND
protocols in that it is transport specific in its address handling.
3.1 Port Mapper Protocol Specification (in RPC Language)
const PMAP_PORT = 111; /* portmapper port number */
/*
* A mapping of (program, version, protocol) to port number:
*/
struct pmap {
unsigned int pm_prog;
unsigned int pm_vers;
unsigned int pm_prot;
unsigned int pm_port;
};
/*
* Supported values for the "pm_prot" field:
*/
const PMAP_IPPROTO_TCP = 6; /* protocol number for TCP/IP */
const PMAP_IPPROTO_UDP = 17; /* protocol number for UDP/IP */
/*
* A list of mappings:
*/
struct pmaplist {
pmap pml_map;
pmaplist *pml_next;
};
typedef pmaplist *pmaplist_ptr;
/*
* Arguments to callit:
*/
struct rmtcallargs {
unsigned int prog;
unsigned int vers;
unsigned int proc;
opaque args<>;
};
/*
* Results of callit:
*/
struct rmtcallres {
unsigned int port;
opaque res<>;
};
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/*
* Port mapper procedures:
*/
program PMAP_PROG {
version PMAP_VERS {
void
PMAPPROC_NULL(void) = 0;
bool
PMAPPROC_SET(pmap) = 1;
bool
PMAPPROC_UNSET(pmap) = 2;
unsigned int
PMAPPROC_GETPORT(pmap) = 3;
pmaplist_ptr
PMAPPROC_DUMP(void) = 4;
rmtcallres
PMAPPROC_CALLIT(rmtcallargs)= 5;
} = 2;
} = 100000;
3.2 Port Mapper Operation
The portmapper program currently supports two protocols (UDP and TCP). The
portmapper is contacted by talking to it on assigned port number 111
(ONCRPC) on either of these protocols.
The following is a description of each of the portmapper procedures:
PMAPPROC_NULL:
This procedure does no work. By convention, procedure zero of any protocol
takes no parameters and returns no results.
PMAPPROC_SET:
When a program first becomes available on a machine, it registers itself
with the port mapper program on the same machine. The program passes its
program number "pm_prog", version number "pm_vers", transport protocol
number "pm_prot", and the port "pm_port" on which it awaits service
request. The procedure returns a boolean reply whose value is "TRUE" if
the procedure successfully established the mapping and "FALSE" otherwise.
The procedure refuses to establish a mapping if one already exists for the
tuple "(pm_prog, pm_vers, pm_prot)".
PMAPPROC_UNSET:
When a program becomes unavailable, it should unregister itself with the
port mapper program on the same machine. The parameters and results have
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meanings identical to those of "PMAPPROC_SET". The protocol and port
number fields of the argument are ignored.
PMAPPROC_GETPORT:
Given a program number "pm_prog", version number "pm_vers", and transport
protocol number "pm_prot", this procedure returns the port number on which
the program is awaiting call requests. A port value of zeros means the
program has not been registered. The "pm_port" field of the argument is
ignored.
PMAPPROC_DUMP:
This procedure enumerates all entries in the port mapper's database. The
procedure takes no parameters and returns a list of program, version,
protocol, and port values.
PMAPPROC_CALLIT:
This procedure allows a client to call another remote procedure on the same
machine without knowing the remote procedure's port number. It is intended
for supporting broadcasts to arbitrary remote programs via the well-known
port mapper's port. The parameters "prog", "vers", "proc", and the bytes
of "args" are the program number, version number, procedure number, and
parameters of the remote procedure. Note:
(1) This procedure only sends a reply if the procedure was successfully
executed and is silent (no reply) otherwise.
(2) The port mapper communicates with the remote program using UDP only.
The procedure returns the remote program's port number, and the reply is
the reply of the remote procedure.
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4. Security Considerations
Additional information about vulnerabilities of certain implementations of
the rpcbind and Port Mapper protocols can be found in "Firewalls and
Internet Security"[4].
4.1 Address Registration and Unregistration
The rpcbind protocol specifies that the RPCBPROC_SET and RPCBPROC_UNSET
procedures only be accepted from the same machine on which rpcbind is
running. The intention is that only the local owner of the service be
allowed to unset the registration for the RPC program. Some
implementations extend this requirement by only allowing RPCBPROC_SET and
RPCBPROC_UNSET procedures to be invoked over a secure machine-local
transport through which the identity of the owner can be directly verified
by rpcbind.
The Port Mapper protocol does not specify that the PMAPPROC_SET and
PMAPPROC_UNSET procedures are only accepted from the local machine, and
many early implementions of the port mapper service accepted these requests
from any machine on the network. As a result, any user would be able to
unregister an RPC program on such systems, and register potentially
spurious information about the service in its place.
Systems supporting the Port Mapper protocol are encouraged to restrict
registration and unregistration requests to the local system.
Implementations should be careful to also disallow portmapper requests
which are made through the PMAPPROC_CALLIT procedure, as these operations
will appear to originate from the local system.
Where possible, portmapper implementation should further restrict
PMAPPROC_SET and PMAPPROC_UNSET operations to a secure machine-local
transport, as described above for rpcbind. Although the Port Mapper
protocol does not include an "owner" field in the PMAPPROC_SET and
PMAPPROC_UNSET arguments, an implementation using such a secure machine-
local transport which conveys the caller's identity can record this
identity in its internal registration records, and allow only the same user
to unregister the service.
4.2 RPCBPROC_CALLIT, RPCBPROC_INDIRECT, and PMAPPROC_CALLIT
The procedures listed in this section's header implement two types of
special RPC operations: Broadcast RPC and Indirect RPC. Both use rpcbind
or the portmapper to forward a request from a remote caller to an RPC
program on the local system. As a result, the request appears to originate
from the local system. RPC programs that provide sensitive services should
examine the address of the caller to determine whether the request
originated from rpcbind or portmapper, in which case the request should be
handled as though it came from a remote system.
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5. References
[1] "Remote Procedure Call Protocol Version 2",
draft-ietf-oncrpc-rpcv2-02.txt, 1996.
[2] "XDR: External Data Representation Standard",
draft-ietf-oncrpc-xdr-01.txt, 1994.
[3] "Requirements for Internet Hosts -- Application and Support", STD-3,
October 1989.
[4] Cheswick, W.R., and Bellovin, S.M., "Firewalls and Internet Security,"
Addison-Wesley, 1994.
6. AUTHOR'S ADDRESS
Stephen X. Nahm
Sun Microsystems, Inc.
2550 Garcia Avenue
Mountain View, CA 94043
Phone: +1 (415) 786-5086
E-mail: sxn@sun.com
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