RCMD(3) | Library Functions Manual | RCMD(3) |
rcmd
, rresvport
,
iruserok
, ruserok
,
rcmd_af
, rresvport_af
,
iruserok_sa
— routines for
returning a stream to a remote command
Standard C Library (libc, -lc)
#include
<unistd.h>
int
rcmd
(char
**ahost, int
inport, const char
*locuser, const char
*remuser, const char
*cmd, int
*fd2p);
int
rresvport
(int
*port);
int
iruserok
(u_long
raddr, int
superuser, const char
*ruser, const char
*luser);
int
ruserok
(const
char *rhost, int
superuser, const char
*ruser, const char
*luser);
int
rcmd_af
(char
**ahost, int
inport, const char
*locuser, const char
*remuser, const char
*cmd, int *fd2p,
int af);
int
rresvport_af
(int
*port, int af);
int
iruserok_sa
(const
void *addr, int
addrlen, int
superuser, const char
*ruser, const char
*luser);
The
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
rresvport
() function returns a descriptor to a
socket with an address in the privileged port space. The
ruserok
() function is used by servers to
authenticate clients requesting service with rcmd
().
All three functions are present in the same file and are used by the
rshd(8) server (among others).
The
rcmd
()
function looks up the host *ahost using
gethostbyname(3), returning -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 residing at the well-known
Internet port inport.
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 0, then the
stderr
(unit 2 of the remote command) will be made the same as the
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.
The protocol is described in detail in rshd(8).
The
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
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.
The
iruserok
()
and ruserok
() functions take a remote host's IP
address or name, as returned by the 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
NOT the
super-user, 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 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
“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.
The
iruserok
()
function is strongly preferred for security reasons. It requires trusting
the local DNS at most, while the ruserok
() function
requires trusting the entire DNS, which can be spoofed.
The functions with an
“_af
” or
“_sa
” suffix, i.e.,
rcmd_af
(),
rresvport_af
()
and
iruserok_sa
(),
work the same as the corresponding functions without a suffix, except that
they are capable of handling both IPv6 and IPv4 ports.
The “_af
” suffix means that
the function has an additional af argument which is
used to specify the address family, (see below). The
af argument extension is implemented for functions
that have no binary address argument. Instead, the af
argument specifies which address family is desired.
The “_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 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.
The functions with neither an
“_af
” suffix nor an
“_sa
” suffix work for IPv4 only,
except for
ruserok
()
which can handle both IPv6 and IPv4. To switch the address family, the
af argument must be filled with
AF_INET
, or AF_INET6
. For
rcmd_af
(), PF_UNSPEC
is also
allowed.
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
() function returns 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.''
rlogin(1), rsh(1), intro(2), rexec(3), rexecd(8), rlogind(8), rshd(8)
W. Stevens and M. Thomas, Advanced Socket API for IPv6, RFC2292.
W. Stevens, M. Thomas, and E. Nordmark, Advanced Socket API for IPv6, draft-ietf-ipngwg-rfc2292bis-01.txt.
Most of these functions appeared in
4.2BSD. rresvport_af
()
appeared in RFC2292, and was implemented by the WIDE project for the
Hydrangea IPv6 protocol stack kit. rcmd_af
()
appeared in draft-ietf-ipngwg-rfc2292bis-01.txt, and was implemented in the
WIDE/KAME IPv6 protocol stack kit. iruserok_sa
()
appeared in discussion on the IETF ipngwg mailing list, and was implemented
in FreeBSD 4.0.
March 3, 2000 | Mac OS X 12 |