rcmd, rcmd_af, rresvport, rresvport_af, iruserok, ruserok,
routines for returning a stream to a remote command
rcmd(char **ahost, int inport, const char *locuser, const
const char *cmd, int *fd2p);
rcmd_af(char **ahost, int inport, const char *locuser,
const char *remuser, const char *cmd, int *fd2p, int
rresvport_af(int *port, int af);
iruserok(u_int32_t raddr, int superuser, const char *ruser,
const char *luser);
ruserok(const char *rhost, int superuser, const char *ruser,
const char *luser);
iruserok_sa(const void *sa, int salen, int superuser, const
const char *luser);
The rcmd() function is used by the superuser to execute a
command on a
remote machine using an authentication scheme based on reserved port numbers.
If the calling process is not setuid, the RSH environment variable
is set, and inport is ``shell/tcp'', rcmdsh(3) is called instead with the
value of RSH. Alternately, if the user is not the superuser, rcmd() will
invoke rcmdsh(3) to run the command via rsh(1). While
rcmd() can handle
IPv4 cases only, the rcmd_af() function can handle other
cases as well.
The rresvport() and rresvport_af() functions return a descriptor to a
socket with an address in the privileged port space. The
ruserok() functions are used by servers to authenticate
service with rcmd(). All four 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 user
is not the
superuser, the only valid port is ``shell/tcp'' (usually
If the connection succeeds, a socket in the Internet domain
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
as being UNIX signal numbers, to be forwarded to the process
group of the
command. If fd2p is NULL, then the standard error (unit 2
of the remote
command) will be made the same as the standard output and no
made for sending arbitrary signals to the remote process,
may be able to get its attention by using out-of-band data.
Note that if
the user is not the superuser, fd2p must be NULL.
rcmd_af() takes address family in the last argument. If the
is PF_UNSPEC, interpretation of *ahost will obey the
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
those in the range 0 to IPPORT_RESERVED - 1, which happens
to be 1023.
Only the superuser is allowed to bind an address of this
sort to a socket.
rresvport() and rresvport_af() need to be seeded with a
if that port is not available these functions will find another.
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 superuser. Then, if the user
is not the
superuser, it checks the /etc/hosts.equiv file. If that
lookup is not
done, or is unsuccessful, the .rhosts in the local user's
is checked to see if the request for service is allowed.
If this file does not exist, is not a regular file, is owned
other than the user or the superuser, or is writeable by
than the owner, the check automatically fails. Zero is returned if the
machine name is listed in the hosts.equiv file, or the host
user name are found in the .rhosts file; otherwise
ruserok() return -1. If the local domain (as obtained from
gethostname(3)) is the same as the remote domain, only the
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,
ruserok() can handle other address families as well, like
first argument of iruserok_sa() is typed as void * to avoid
between <unistd.h> and <sys/socket.h>.
The rcmd() function returns a valid socket descriptor on
success. It returns
-1 on error and prints a diagnostic message on the
The rresvport() and rresvport_af() functions return a valid,
descriptor on success. It returns -1 on error with the
errno set according to the reason for failure. The error
code EAGAIN is
overloaded to mean ``all network ports in use''.
rsh(1), intro(2), bindresvport(3), bindresvport_sa(3),
These functions appeared in 4.2BSD.
OpenBSD 3.6 June 4, 1993
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