xref: /freebsd/lib/libc/net/rcmd.3 (revision 732a02b4e77866604a120a275c082bb6221bd2ff)
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28.\"     From: @(#)rcmd.3	8.1 (Berkeley) 6/4/93
29.\" $FreeBSD$
30.\"
31.Dd March 3, 2000
32.Dt RCMD 3
33.Os
34.Sh NAME
35.Nm rcmd ,
36.Nm rresvport ,
37.Nm iruserok ,
38.Nm ruserok ,
39.Nm rcmd_af ,
40.Nm rresvport_af ,
41.Nm iruserok_sa
42.Nd routines for returning a stream to a remote command
43.Sh LIBRARY
44.Lb libc
45.Sh SYNOPSIS
46.In unistd.h
47.Ft int
48.Fn rcmd "char **ahost" "int inport" "const char *locuser" "const char *remuser" "const char *cmd" "int *fd2p"
49.Ft int
50.Fn rresvport "int *port"
51.Ft int
52.Fn iruserok "u_long raddr" "int superuser" "const char *ruser" "const char *luser"
53.Ft int
54.Fn ruserok "const char *rhost" "int superuser" "const char *ruser" "const char *luser"
55.Ft int
56.Fn rcmd_af "char **ahost" "int inport" "const char *locuser" "const char *remuser" "const char *cmd" "int *fd2p" "int af"
57.Ft int
58.Fn rresvport_af "int *port" "int af"
59.Ft int
60.Fn iruserok_sa "const void *addr" "int addrlen" "int superuser" "const char *ruser" "const char *luser"
61.Sh DESCRIPTION
62The
63.Fn rcmd
64function
65is used by the super-user to execute a command on
66a remote machine using an authentication scheme based
67on reserved port numbers.
68The
69.Fn rresvport
70function
71returns a descriptor to a socket
72with an address in the privileged port space.
73The
74.Fn ruserok
75function
76is used by servers
77to authenticate clients requesting service with
78.Fn rcmd .
79All three functions are present in the same file and are used
80by the
81.Xr rshd 8
82server (among others).
83.Pp
84The
85.Fn rcmd
86function
87looks up the host
88.Fa *ahost
89using
90.Xr gethostbyname 3 ,
91returning -1 if the host does not exist.
92Otherwise
93.Fa *ahost
94is set to the standard name of the host
95and a connection is established to a server
96residing at the well-known Internet port
97.Fa inport .
98.Pp
99If the connection succeeds,
100a socket in the Internet domain of type
101.Dv SOCK_STREAM
102is returned to the caller, and given to the remote
103command as
104.Dv stdin
105and
106.Dv stdout .
107If
108.Fa fd2p
109is non-zero, then an auxiliary channel to a control
110process will be set up, and a descriptor for it will be placed
111in
112.Fa *fd2p .
113The control process will return diagnostic
114output from the command (unit 2) on this channel, and will also
115accept bytes on this channel as being
116.Ux
117signal numbers, to be
118forwarded to the process group of the command.
119If
120.Fa fd2p
121is 0, then the
122.Dv stderr
123(unit 2 of the remote
124command) will be made the same as the
125.Dv stdout
126and no
127provision is made for sending arbitrary signals to the remote process,
128although you may be able to get its attention by using out-of-band data.
129.Pp
130The protocol is described in detail in
131.Xr rshd 8 .
132.Pp
133The
134.Fn rresvport
135function is used to obtain a socket to which an address with a Privileged
136Internet port is bound.
137This socket is suitable for use by
138.Fn rcmd
139and several other functions.
140Privileged Internet ports are those in the range 0 to 1023.
141Only the super-user is allowed to bind an address of this sort
142to a socket.
143.Pp
144The
145.Fn iruserok
146and
147.Fn ruserok
148functions take a remote host's IP address or name, as returned by the
149.Xr gethostbyname 3
150routines, two user names and a flag indicating whether the local user's
151name is that of the super-user.
152Then, if the user is
153.Em NOT
154the super-user, it checks the
155.Pa /etc/hosts.equiv
156file.
157If that lookup is not done, or is unsuccessful, the
158.Pa .rhosts
159in the local user's home directory is checked to see if the request for
160service is allowed.
161.Pp
162If this file does not exist, is not a regular file, is owned by anyone
163other than the user or the super-user, or is writable by anyone other
164than the owner, the check automatically fails.
165Zero is returned if the machine name is listed in the
166.Dq Pa hosts.equiv
167file, or the host and remote user name are found in the
168.Dq Pa .rhosts
169file; otherwise
170.Fn iruserok
171and
172.Fn ruserok
173return -1.
174If the local domain (as obtained from
175.Xr gethostname 3 )
176is the same as the remote domain, only the machine name need be specified.
177.Pp
178The
179.Fn iruserok
180function is strongly preferred for security reasons.
181It requires trusting the local DNS at most, while the
182.Fn ruserok
183function requires trusting the entire DNS, which can be spoofed.
184.Pp
185The functions with an
186.Dq Li _af
187or
188.Dq Li _sa
189suffix, i.e.,
190.Fn rcmd_af ,
191.Fn rresvport_af
192and
193.Fn iruserok_sa ,
194work the same as the corresponding functions without a
195suffix, except that they are capable of handling both IPv6 and IPv4 ports.
196.Pp
197The
198.Dq Li _af
199suffix means that the function has an additional
200.Fa af
201argument which is used to specify the address family,
202(see below).
203The
204.Fa af
205argument extension is implemented for functions
206that have no binary address argument.
207Instead, the
208.Fa af
209argument specifies which address family is desired.
210.Pp
211The
212.Dq Li _sa
213suffix means that the function has general socket address and
214length arguments.
215As the socket address is a protocol independent data structure,
216IPv4 and IPv6 socket address can be passed as desired.
217The
218.Fa sa
219argument extension is implemented for functions
220that pass a protocol dependent binary address argument.
221The argument needs to be replaced with a more general address structure
222to support multiple address families in a general way.
223.Pp
224The functions with neither an
225.Dq Li _af
226suffix nor an
227.Dq Li _sa
228suffix work for IPv4 only, except for
229.Fn ruserok
230which can handle both IPv6 and IPv4.
231To switch the address family, the
232.Fa af
233argument must be filled with
234.Dv AF_INET ,
235or
236.Dv AF_INET6 .
237For
238.Fn rcmd_af ,
239.Dv PF_UNSPEC
240is also allowed.
241.Sh ENVIRONMENT
242.Bl -tag -width RSH
243.It Ev RSH
244When using the
245.Fn rcmd
246function, this variable is used as the program to run instead of
247.Xr rsh 1 .
248.El
249.Sh DIAGNOSTICS
250The
251.Fn rcmd
252function
253returns a valid socket descriptor on success.
254It returns -1 on error and prints a diagnostic message
255on the standard error.
256.Pp
257The
258.Fn rresvport
259function
260returns a valid, bound socket descriptor on success.
261It returns -1 on error with the global value
262.Va errno
263set according to the reason for failure.
264The error code
265.Er EAGAIN
266is overloaded to mean ``All network ports in use.''
267.Sh SEE ALSO
268.Xr rlogin 1 ,
269.Xr rsh 1 ,
270.Xr intro 2 ,
271.Xr rlogind 8 ,
272.Xr rshd 8
273.Pp
274.Rs
275.%A W. Stevens
276.%A M. Thomas
277.%T "Advanced Socket API for IPv6"
278.%O RFC2292
279.Re
280.Rs
281.%A W. Stevens
282.%A M. Thomas
283.%A E. Nordmark
284.%T "Advanced Socket API for IPv6"
285.%O RFC3542
286.Re
287.Sh HISTORY
288Most of these
289functions appeared in
290.Bx 4.2 .
291The
292.Fn rresvport_af
293function
294appeared in RFC2292, and was implemented by the WIDE project
295for the Hydrangea IPv6 protocol stack kit.
296The
297.Fn rcmd_af
298function
299appeared in draft-ietf-ipngwg-rfc2292bis-01.txt,
300and was implemented in the WIDE/KAME IPv6 protocol stack kit.
301The
302.Fn iruserok_sa
303function
304appeared in discussion on the IETF ipngwg mailing list,
305and was implemented in
306.Fx 4.0 .
307