rcmd(3)

NAME

rcmd, rresvport, iruserok, ruserok, rcmd_af, rresvport_af,
iruserok_sa routines for returning a stream to a remote command

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <unistd.h>
int
rcmd(char  **ahost,  int  inport, const char *locuser, const
char *remuser,
        const char *cmd, int *fd2p);
int
rresvport(int *port);
int
iruserok(u_long raddr, int superuser, const char *ruser,
        const char *luser);
int
ruserok(const char *rhost, int superuser, const char *ruser,
        const char *luser);
int
rcmd_af(char **ahost, int inport, const char *locuser,
        const char *remuser, const char *cmd, int *fd2p, int
af);
int
rresvport_af(int *port, int af);
int
iruserok_sa(const void *addr, int addrlen, int superuser,
        const char *ruser, const char *luser);

DESCRIPTION

The rcmd() function is used by the super-user to execute a
command on a remote machine using an authentication scheme based on re
served port numbers. The rresvport() function returns a descriptor to a
socket with an
address in the privileged port space. The ruserok() func
tion is used by servers to authenticate clients requesting service with
rcmd(). All
three functions are present in the same file and are used by
the rshd(8) server (among others).
The rcmd() function looks up the host *ahost using gethost
byname(3), returning -1 if the host does not exist. Otherwise *ahost
is set to the standard name of the host and a connection is established to
a server residing at the well-known Internet port inport.
If the connection succeeds, a socket in the Internet domain
of type SOCK_STREAM is returned to the caller, and given to the re
mote command as stdin and stdout. If fd2p is non-zero, then an auxiliary
channel to a control process will be set up, and a descriptor for it will
be placed in *fd2p. The control process will return diagnostic output
from the command (unit 2) on this channel, and will also accept bytes on
this channel as being UNIX signal numbers, to be forwarded to the process
group of the command. If fd2p is 0, then the stderr (unit 2 of the re
mote command) will be made the same as the stdout and no provision is made
for sending arbitrary signals to the remote process, although you may be
able to get its attention by using out-of-band data.
The protocol is described in detail in rshd(8).
The rresvport() function is used to obtain a socket to which
an address with a Privileged Internet port is bound. This socket is
suitable for
use by rcmd() and several other functions. Privileged In
ternet ports are those in the range 0 to 1023. Only the super-user is al
lowed to bind an address of this sort to a socket.
The iruserok() and ruserok() functions take a remote host's
IP address or name, as returned by the gethostbyname(3) routines, two user
names and a flag indicating whether the local user's name is that of the
super-user. Then, if the user is NOT the super-user, it checks the
/etc/hosts.equiv file. If that lookup is not done, or is unsuccessful, the
.rhosts in the local user's home directory is checked to see if the request
for service is allowed.
If this file does not exist, is not a regular file, is owned
by anyone other than the user or the super-user, or is writable by
anyone other than the owner, the check automatically fails. Zero is re
turned if the machine name is listed in the ``hosts.equiv'' file, or the
host and remote user name are found in the ``.rhosts'' file; other
wise iruserok()
and ruserok() return -1. If the local domain (as obtained
from gethostname(3)) is the same as the remote domain, only the
machine name need be specified.
The iruserok() function is strongly preferred for security
reasons. It
requires trusting the local DNS at most, while the ruserok()
function requires trusting the entire DNS, which can be spoofed.
The functions with an ``_af'' or ``_sa'' suffix, i.e.,
rcmd_af(),
rresvport_af() and iruserok_sa(), work the same as the cor
responding functions without a suffix, except that they are capable of
handling both IPv6 and IPv4 ports.
The ``_af'' suffix means that the function has an additional
af argument which is used to specify the address family, (see below).
The af argument extension is implemented for functions that have no bi
nary address argument. Instead, the af argument specifies which address
family is desired.
The ``_sa'' suffix means that the function has general sock
et address and length arguments. As the socket address is a protocol inde
pendent data structure, IPv4 and IPv6 socket address can be passed as de
sired. The sa argument extension is implemented for functions that pass a
protocol dependent binary address argument. The argument needs to be
replaced with a more general address structure to support multiple
address families in a general way.
The functions with neither an ``_af'' suffix nor an ``_sa''
suffix work
for IPv4 only, except for ruserok() which can handle both
IPv6 and IPv4. To switch the address family, the af argument must be filled
with
AF_INET, or AF_INET6. For rcmd_af(), PF_UNSPEC is also al
lowed.

DIAGNOSTICS

The rcmd() function returns a valid socket descriptor on
success. It returns -1 on error and prints a diagnostic message on the
standard error.
The rresvport() function returns a valid, bound socket de
scriptor on success. It returns -1 on error with the global value errno
set according to the reason for failure. The error code EAGAIN is over
loaded to mean ``All network ports in use.''

HISTORY

Most of these functions appeared in 4.2BSD. The
rresvport_af() function
appeared in RFC2292, and was implemented by the WIDE project
for the
Hydrangea IPv6 protocol stack kit. The rcmd_af() function
appeared in draft-ietf-ipngwg-rfc2292bis-01.txt, and was implemented in
the WIDE/KAME
IPv6 protocol stack kit. The iruserok_sa() function ap
peared in discussion on the IETF ipngwg mailing list, and was implemented in
FreeBSD 4.0.
BSD March 3, 2000

docs.sk

comprehensive documentation repository

See also

rcmd(3)

NAME

LIBRARY

SYNOPSIS

DESCRIPTION

DIAGNOSTICS

SEE ALSO

HISTORY