rcmd, orcmd, rcmd_af, orcmd_af, rresvport, rresvport_af, iruserok,
ruserok, iruserok_sa - routines for returning a stream to a remote command
Standard C Library (libc, -lc)
#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
rcmd_af(char **ahost, int inport, const char *locuser,
const char *remuser, const char *cmd, int *fd2p, int af);
int
orcmd_af(char **ahost, int inport, const char *locuser,
const char *remuser, const char *cmd, int *fd2p, int af);
int
rresvport(int *port);
int
rresvport_af(int *port, int family);
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);
int
iruserok_sa(const void *raddr, int rlen, int superuser,
const char *ruser, const char *luser);
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. While rcmd() and orcmd() can only handle
IPv4 address in the first argument, rcmd_af() and orcmd_af() can handle
other cases as well. The rresvport() function returns a descriptor to a
socket with an address in the privileged port space. The rresvport_af()
function is similar to rresvport(), but you can explicitly specify the
address family to use. Calling rresvport_af() with AF_INET has the same
effect as rresvport(). The iruserok() and ruserok() functions are used
by servers to authenticate clients requesting service with rcmd(). All
six functions are present in the same file and are used by the rshd(8)
server (among others). iruserok_sa() is an address family independent
variant of iruserok().
The rcmd() function looks up the host *ahost using gethostbyname(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 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 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 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.
rcmd_af() and orcmd_af() take address family in the last argument. If
the last argument is PF_UNSPEC, interpretation of *ahost will obey the
underlying address resolution like DNS.
The protocol is described in detail in rshd(8).
The rresvport() and rresvport_af() functions are used to obtain a socket
with a privileged address 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
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 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
remote 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
server for the remote host's domain.
While iruserok() can handle IPv4 addresses only, iruserok_sa() and
ruserok() can handle other address families as well, like IPv6. The
first argument of iruserok_sa() is typed as void * to avoid dependency
between <unistd.h> and <sys/socket.h>.
RCMD_CMD When using the rcmd() function, this variable is used as the
program to run instead of rcmd(1).
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() and rresvport_af() function return a valid, bound socket
descriptor on success. They return -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.''
rcmd(1), rlogin(1), rsh(1), intro(2), rexec(3), hosts.equiv(5),
rhosts(5), rexecd(8), rlogind(8), rshd(8)
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. rcmd_af() and rresvport_af() were
defined in RFC2292.
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.
BSD June 4, 1993 BSD
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