ruserok(3)
- NetBSD Manual Pages
RCMD(3) NetBSD Programmer's Manual RCMD(3)
NAME
rcmd, rresvport, iruserok, ruserok, orcmd - 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
orcmd(char **ahost, int inport, const char *locuser, const char *remuser,
const char *cmd, int *fd2p);
int
rresvport(int *port);
int
iruserok(u_int32_t raddr, int superuser, const char *ruser,
const char *luser);
int
ruserok(const char *rhost, int superuser, const char *ruser,
const char *luser);
DESCRIPTION
The rcmd() function is available for use by anyone to run commands on a
remote system. It acts like the orcmd() command, with the exception that
it makes a call out to the rcmd(1) command, or any other user-specified
command, to perform the actual connection (thus not requiring that the
caller be running as the super-user), and is only available for the
``shell/tcp'' port. The orcmd() function is used by the super-user to
execute a command on a remote machine using an authentication scheme
based on reserved port numbers. The rresvport() function returns a de-
scriptor to a socket with an address in the privileged port space. The
iruserok() and ruserok() functions are used by servers to authenticate
clients requesting service with rcmd(). All five 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 gethostbyname(3), re-
turning -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 re-
siding 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 remote 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 com-
mand (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 remote 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 with a privileged ad-
dress bound to it. This socket is suitable for use by rcmd() and several
other functions. Privileged Internet ports are those in the range 0 to
1023. Only the super-user is allowed to bind an address of this sort to
a socket.
The iruserok() and ruserok() functions take a remote host's IP address or
name, respectively, two user names and a flag indicating whether the lo-
cal 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 writeable by anyone other
than the owner, the check automatically fails. Zero is returned if the
machine name is listed in the ``hosts.equiv'' file, or the host and re-
mote user name are found in the ``.rhosts'' file; otherwise 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.
If the IP address of the remote host is known, iruserok() should be used
in preference to ruserok(), as it does not require trusting the DNS serv-
er for the remote host's domain.
DIAGNOSTICS
The rcmd() function returns a valid socket descriptor on success. It re-
turns -1 on error and prints a diagnostic message on the standard error.
The rresvport() function returns a valid, bound socket descriptor on suc-
cess. It returns -1 on error with the global value errno set according
to the reason for failure. The error code EAGAIN is overloaded to mean
``All network ports in use.''
ENVIRONMENT
RCMD_CMD When using the rcmd() function, this variable is used as the
program to run instead of rcmd(1).
SEE ALSO
rcmd(1), rlogin(1), rsh(1), intro(2), rexec(3), hosts.equiv(5),
rhosts(5), rexecd(8), rlogind(8), rshd(8).
HISTORY
The orcmd(), rresvport(), iruserok() and ruserok() functions appeared in
4.2BSD, where the orcmd() function was called rcmd.() The (newer) rcmd()
function appeared in NetBSD 1.3.
BUGS
As the rcmd function uses getpwent(3) functions, passing in a previous
value from one of this family of functions can result in unpredictable
results. Do not write code like the following:
struct passwd *pw;
pw = getpwuid(getuid());
if (rcmd(host, port, pw->pw_name, pw->pw_name, cmd, fd2p) < 0)
err(1, "rcmd");
When a reentrant version of getpwent(3) is available, rcmd should be
changed to use this instead.
NetBSD 1.4 June 4, 1993 2
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