.\" $NetBSD: rcmd.3,v 1.16 1998/04/28 06:00:53 fair Exp $ .\" .\" Copyright (c) 1983, 1991, 1993 .\" The Regents of the University of California. All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. All advertising materials mentioning features or use of this software .\" must display the following acknowledgement: .\" This product includes software developed by the University of .\" California, Berkeley and its contributors. .\" 4. Neither the name of the University nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" @(#)rcmd.3 8.1 (Berkeley) 6/4/93 .\" .Dd June 4, 1993 .Dt RCMD 3 .Os BSD 4.2 .Sh NAME .Nm rcmd , .Nm rresvport , .Nm iruserok , .Nm ruserok , .Nm orcmd .Nd routines for returning a stream to a remote command .Sh LIBRARY .Lb libc .Sh SYNOPSIS .Fd #include .Ft int .Fn rcmd "char **ahost" "int inport" "const char *locuser" "const char *remuser" "const char *cmd" "int *fd2p" .Ft int .Fn orcmd "char **ahost" "int inport" "const char *locuser" "const char *remuser" "const char *cmd" "int *fd2p" .Ft int .Fn rresvport "int *port" .Ft int .Fn iruserok "u_int32_t raddr" "int superuser" "const char *ruser" "const char *luser" .Ft int .Fn ruserok "const char *rhost" "int superuser" "const char *ruser" "const char *luser" .Sh DESCRIPTION The .Fn rcmd function is available for use by anyone to run commands on a remote system. It acts like the .Fn orcmd command, with the exception that it makes a call out to the .Xr 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 .Dq shell/tcp port. The .Fn 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 .Fn rresvport function returns a descriptor to a socket with an address in the privileged port space. The .Fn iruserok and .Fn ruserok functions are used by servers to authenticate clients requesting service with .Fn rcmd . All five functions are present in the same file and are used by the .Xr rshd 8 server (among others). .Pp The .Fn rcmd function looks up the host .Fa *ahost using .Xr gethostbyname 3 , returning \-1 if the host does not exist. Otherwise .Fa *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 .Fa inport . .Pp If the connection succeeds, a socket in the Internet domain of type .Dv SOCK_STREAM is returned to the caller, and given to the remote command as .Em stdin and .Em stdout . If .Fa 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 .Fa *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 .Ux signal numbers, to be forwarded to the process group of the command. If .Fa fd2p is 0, then the .Em stderr (unit 2 of the remote command) will be made the same as the .Em 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. .Pp The protocol is described in detail in .Xr rshd 8 . .Pp The .Fn rresvport function is used to obtain a socket with a privileged address bound to it. This socket is suitable for use by .Fn 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. .Pp The .Fn iruserok and .Fn 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 .Em NOT the super-user, it checks the .Pa /etc/hosts.equiv file. If that lookup is not done, or is unsuccessful, the .Pa .rhosts in the local user's home directory is checked to see if the request for service is allowed. .Pp 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 .Dq Pa hosts.equiv file, or the host and remote user name are found in the .Dq Pa .rhosts file; otherwise .Fn iruserok and .Fn ruserok return \-1. If the local domain (as obtained from .Xr gethostname 3 ) is the same as the remote domain, only the machine name need be specified. .Pp If the IP address of the remote host is known, .Fn iruserok should be used in preference to .Fn ruserok , as it does not require trusting the DNS server for the remote host's domain. .Sh DIAGNOSTICS The .Fn rcmd function returns a valid socket descriptor on success. It returns \-1 on error and prints a diagnostic message on the standard error. .Pp The .Fn rresvport function returns a valid, bound socket descriptor on success. It returns \-1 on error with the global value .Va errno set according to the reason for failure. The error code .Dv EAGAIN is overloaded to mean ``All network ports in use.'' .Sh ENVIRONMENT .Bl -tag -width RCMD_CMDxx -compact .It Ev RCMD_CMD When using the .Fn rcmd function, this variable is used as the program to run instead of .Xr rcmd 1 . .El .Sh SEE ALSO .Xr rcmd 1 , .Xr rlogin 1 , .Xr rsh 1 , .Xr intro 2 , .Xr rexec 3 , .Xr hosts.equiv 5 , .Xr rhosts 5 , .Xr rexecd 8 , .Xr rlogind 8 , .Xr rshd 8 . .Sh HISTORY The .Fn orcmd , .Fn rresvport , .Fn iruserok and .Fn ruserok functions appeared in .Bx 4.2 , where the .Fn orcmd function was called .Fn rcmd. The (newer) .Fn rcmd function appeared in .Nx 1.3 . .Sh BUGS As the .Nm function uses .Xr 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: .Bd -literal -offset indent struct passwd *pw; pw = getpwuid(getuid()); ... if (rcmd(host, port, pw->pw_name, pw->pw_name, cmd, fd2p) < 0) err(1, "rcmd"); .Ed .Pp When a reentrant version of .Xr getpwent 3 is available, .Nm should be changed to use this instead.