RCMD(3)                   OpenBSD Programmer's Manual                  RCMD(3)

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

SYNOPSIS
     #include <unistd.h>

     int
     rcmd(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
     rresvport(int *port);

     int
     rresvport_af(int *port, int af);

     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 *sa, int salen, int superuser, const char *ruser,
             const char *luser);

DESCRIPTION
     The rcmd() function is used by the superuser to execute a command on a
     remote machine using an authentication scheme based on reserved port num-
     bers.  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 iruserok() and
     ruserok() functions are used by servers to authenticate clients request-
     ing 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), 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 user is not the
     superuser, the only valid port is ``shell/tcp'' (usually port 514).

     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 NULL, then the standard error (unit 2 of the remote
     command) will be made the same as the standard output 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.  Note that if
     the user is not the superuser, fd2p must be NULL.

     rcmd_af() takes address family in the last argument.  If the last argu-
     ment is PF_UNSPEC, interpretation of *ahost will obey the underlying ad-
     dress 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 IPPORT_RESERVED - 1, which happens to be 1023.
     Only the superuser is allowed to bind an address of this sort to a sock-
     et.  rresvport() and rresvport_af() need to be seeded with a port number;
     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 lo-
     cal 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 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 superuser, 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 serv-
     er 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>.

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() and rresvport_af() functions return a valid, bound socket
     descriptor on success.  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''.

SEE ALSO
     rsh(1), intro(2), bindresvport(3), bindresvport_sa(3), rcmdsh(3), rshd(8)

HISTORY
     These functions appeared in 4.2BSD.

OpenBSD 3.5                      June 4, 1993                                2
