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.Dd March 3, 2000
.Dt RCMD 3
.Os
.Sh NAME
.Nm rcmd ,
.Nm rresvport ,
.Nm iruserok ,
.Nm ruserok ,
.Nm rcmd_af ,
.Nm rresvport_af ,
.Nm iruserok_sa
.Nd routines for returning a stream to a remote command
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In unistd.h
.Ft int
.Fn rcmd "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_long raddr" "int superuser" "const char *ruser" "const char *luser"
.Ft int
.Fn ruserok "const char *rhost" "int superuser" "const char *ruser" "const char *luser"
.Ft int
.Fn rcmd_af "char **ahost" "int inport" "const char *locuser" "const char *remuser" "const char *cmd" "int *fd2p" "int af"
.Ft int
.Fn rresvport_af "int *port" "int af"
.Ft int
.Fn iruserok_sa "const void *addr" "int addrlen" "int superuser" "const char *ruser" "const char *luser"
.Sh DESCRIPTION
The
.Fn rcmd
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 ruserok
function
is used by servers
to authenticate clients requesting service with
.Fn rcmd .
All three 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
.Dv stdin
and
.Dv 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
.Dv stderr
(unit 2 of the remote
command) will be made the same as the
.Dv 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 to which an address with a Privileged
Internet port is bound.
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, as returned by the
.Xr gethostbyname 3
routines, 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 writable 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
The
.Fn iruserok
function is strongly preferred for security reasons.
It requires trusting the local DNS at most, while the
.Fn ruserok
function requires trusting the entire DNS, which can be spoofed.
.Pp
The functions with an
.Dq Li _af
or
.Dq Li _sa
suffix, i.e.,
.Fn rcmd_af ,
.Fn rresvport_af
and
.Fn iruserok_sa ,
work the same as the corresponding functions without a
suffix, except that they are capable of handling both IPv6 and IPv4 ports.
.Pp
The
.Dq Li _af
suffix means that the function has an additional
.Fa af
argument which is used to specify the address family,
(see below).
The
.Fa af
argument extension is implemented for functions
that have no binary address argument.
Instead, the
.Fa af
argument specifies which address family is desired.
.Pp
The
.Dq Li _sa
suffix means that the function has general socket address and
length arguments.
As the socket address is a protocol independent data structure,
IPv4 and IPv6 socket address can be passed as desired.
The
.Fa sa
argument extension is implemented for functions
that pass a protocol dependent binary address argument.
The argument needs to be replaced with a more general address structure
to support multiple address families in a general way.
.Pp
The functions with neither an
.Dq Li _af
suffix nor an
.Dq Li _sa
suffix work for IPv4 only, except for
.Fn ruserok
which can handle both IPv6 and IPv4.
To switch the address family, the
.Fa af
argument must be filled with
.Dv AF_INET ,
or
.Dv AF_INET6 .
For
.Fn rcmd_af ,
.Dv PF_UNSPEC
is also allowed.
.Sh ENVIRONMENT
.Bl -tag -width RSH
.It Ev RSH
When using the
.Fn rcmd
function, this variable is used as the program to run instead of
.Xr rsh 1 .
.El
.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
.Er EAGAIN
is overloaded to mean ``All network ports in use.''
.Sh SEE ALSO
.Xr rlogin 1 ,
.Xr rsh 1 ,
.Xr intro 2 ,
.Xr rlogind 8 ,
.Xr rshd 8
.Pp
.Rs
.%A W. Stevens
.%A M. Thomas
.%T "Advanced Socket API for IPv6"
.%O RFC2292
.Re
.Rs
.%A W. Stevens
.%A M. Thomas
.%A E. Nordmark
.%T "Advanced Socket API for IPv6"
.%O RFC3542
.Re
.Sh HISTORY
Most of these
functions appeared in
.Bx 4.2 .
The
.Fn rresvport_af
function
appeared in RFC2292, and was implemented by the WIDE project
for the Hydrangea IPv6 protocol stack kit.
The
.Fn rcmd_af
function
appeared in draft-ietf-ipngwg-rfc2292bis-01.txt,
and was implemented in the WIDE/KAME IPv6 protocol stack kit.
The
.Fn iruserok_sa
function
appeared in discussion on the IETF ipngwg mailing list,
and was implemented in
.Fx 4.0 .