libc/net/rcmd.3

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.\"     @(#)rcmd.3	8.1 (Berkeley) 6/4/93
.\"
.Dd June 4, 1993
.Dt RCMD 3
.Os
.Sh NAME
.Nm rcmd ,
.Nm orcmd ,
.Nm rcmd_af ,
.Nm orcmd_af ,
.Nm rresvport ,
.Nm rresvport_af ,
.Nm iruserok ,
.Nm ruserok ,
.Nm iruserok_sa
.Nd routines for returning a stream to a remote command
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.Fd #include \*[Lt]unistd.h\*[Gt]
.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 rcmd_af "char **ahost" "int inport" "const char *locuser" "const char *remuser" "const char *cmd" "int *fd2p" "int af"
.Ft int
.Fn orcmd_af "char **ahost" "int inport" "const char *locuser" "const char *remuser" "const char *cmd" "int *fd2p" "int af"
.Ft int
.Fn rresvport "int *port"
.Ft int
.Fn rresvport_af "int *port" "int family"
.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"
.Ft int
.Fn iruserok_sa "const void *raddr" "int rlen" "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.
While
.Fn rcmd
and
.Fn orcmd
can only handle IPv4 address in the first argument,
.Fn rcmd_af
and
.Fn orcmd_af
can handle other cases as well.
The
.Fn rresvport
function
returns a descriptor to a socket
with an address in the privileged port space.
The
.Fn rresvport_af
function is similar to
.Fn rresvport ,
but you can explicitly specify the address family to use.
Calling
.Fn rresvport_af
with
.Dv AF_INET
has the same effect as
.Fn rresvport .
The
.Fn iruserok
and
.Fn ruserok
functions are used by servers
to authenticate clients requesting service with
.Fn rcmd .
All six functions are present in the same file and are used
by the
.Xr rshd 8
server (among others).
.Fn iruserok_sa
is an address family independent variant of
.Fn iruserok .
.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
.Fn rcmd_af
and
.Fn orcmd_af
take address family in the last argument.
If the last argument is
.Dv PF_UNSPEC ,
interpretation of
.Fa *ahost
will obey the underlying address resolution like DNS.
.Pp
The protocol is described in detail in
.Xr rshd 8 .
.Pp
The
.Fn rresvport
and
.Fn rresvport_af
functions are 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.
.Pp
While
.Fn iruserok
can handle IPv4 addresses only,
.Fn iruserok_sa
and
.Fn ruserok
can handle other address families as well, like IPv6.
The first argument of
.Fn iruserok_sa
is typed as
.Fa "void *"
to avoid dependency between
.Aq Li unistd.h
and
.Aq Li sys/socket.h .
.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 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
and
.Fn rresvport_af
function
return a valid, bound socket descriptor on success.
They return \-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 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 .
.Fn rcmd_af
and
.Fn rresvport_af
were defined in RFC2292.
.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-\*[Gt]pw_name, pw-\*[Gt]pw_name, cmd, fd2p) \*[Lt] 0)
	err(1, "rcmd");

.Ed
.Pp
When a reentrant version of
.Xr getpwent 3
is available,
.Nm
should be changed to use this instead.