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 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
ssh(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 requesting service with rcmd
().
iruserok_sa
() is an address family independent
variant of iruserok
().
The
rcmd
()
function looks up the host *ahost using
gethostbyname(3) and, if the host exists,
*ahost is set to the standard name of the host. A
connection is then 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 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 command (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 argument is
PF_UNSPEC
, interpretation of
*ahost will obey the underlying address resolution
like DNS.
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 socket.
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 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 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 server 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 returns -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
ssh(1), intro(2), bindresvport(3), bindresvport_sa(3), rcmdsh(3)
HISTORY
These functions appeared in 4.2BSD.