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1 | .\" $OpenBSD: rcmd.3,v 1.34 2016/05/28 15:48:30 millert Exp $ | ||
2 | .\" | ||
3 | .\" Copyright (c) 1983, 1991, 1993 | ||
4 | .\" The Regents of the University of California. All rights reserved. | ||
5 | .\" | ||
6 | .\" Redistribution and use in source and binary forms, with or without | ||
7 | .\" modification, are permitted provided that the following conditions | ||
8 | .\" are met: | ||
9 | .\" 1. Redistributions of source code must retain the above copyright | ||
10 | .\" notice, this list of conditions and the following disclaimer. | ||
11 | .\" 2. Redistributions in binary form must reproduce the above copyright | ||
12 | .\" notice, this list of conditions and the following disclaimer in the | ||
13 | .\" documentation and/or other materials provided with the distribution. | ||
14 | .\" 3. Neither the name of the University nor the names of its contributors | ||
15 | .\" may be used to endorse or promote products derived from this software | ||
16 | .\" without specific prior written permission. | ||
17 | .\" | ||
18 | .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND | ||
19 | .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE | ||
20 | .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE | ||
21 | .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE | ||
22 | .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL | ||
23 | .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS | ||
24 | .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) | ||
25 | .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT | ||
26 | .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY | ||
27 | .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF | ||
28 | .\" SUCH DAMAGE. | ||
29 | .\" | ||
30 | .Dd $Mdocdate: May 28 2016 $ | ||
31 | .Dt RCMD 3 | ||
32 | .Os | ||
33 | .Sh NAME | ||
34 | .Nm rcmd , | ||
35 | .Nm rcmd_af , | ||
36 | .Nm rresvport , | ||
37 | .Nm rresvport_af , | ||
38 | .Nm ruserok | ||
39 | .Nd routines for returning a stream to a remote command | ||
40 | .Sh SYNOPSIS | ||
41 | .In unistd.h | ||
42 | .Ft int | ||
43 | .Fn rcmd "char **ahost" "int inport" "const char *locuser" "const char *remuser" "const char *cmd" "int *fd2p" | ||
44 | .Ft int | ||
45 | .Fn rcmd_af "char **ahost" "int inport" "const char *locuser" "const char *remuser" "const char *cmd" "int *fd2p" "int af" | ||
46 | .Ft int | ||
47 | .Fn rresvport "int *port" | ||
48 | .Ft int | ||
49 | .Fn rresvport_af "int *port" "int af" | ||
50 | .Ft int | ||
51 | .Fn ruserok "const char *rhost" "int superuser" "const char *ruser" "const char *luser" | ||
52 | .Sh DESCRIPTION | ||
53 | The | ||
54 | .Fn rcmd | ||
55 | function is used by the superuser to execute a command on a remote | ||
56 | machine using an authentication scheme based on reserved | ||
57 | port numbers. | ||
58 | If the calling process is not setuid, the | ||
59 | .Ev RSH | ||
60 | environment variable is set, and | ||
61 | .Fa inport | ||
62 | is | ||
63 | .Dq shell/tcp , | ||
64 | .Xr rcmdsh 3 | ||
65 | is called instead with the value of | ||
66 | .Ev RSH . | ||
67 | Alternately, if the user is not the superuser, | ||
68 | .Fn rcmd | ||
69 | will invoke | ||
70 | .Xr rcmdsh 3 | ||
71 | to run the command via | ||
72 | .Xr ssh 1 . | ||
73 | While | ||
74 | .Fn rcmd | ||
75 | can handle IPv4 cases only, | ||
76 | the | ||
77 | .Fn rcmd_af | ||
78 | function can handle other cases as well. | ||
79 | .Pp | ||
80 | The | ||
81 | .Fn rresvport | ||
82 | and | ||
83 | .Fn rresvport_af | ||
84 | functions return a descriptor to a socket | ||
85 | with an address in the privileged port space. | ||
86 | The | ||
87 | .Fn ruserok | ||
88 | function is used by servers | ||
89 | to authenticate clients requesting service with | ||
90 | .Fn rcmd . | ||
91 | .Pp | ||
92 | The | ||
93 | .Fn rcmd | ||
94 | function looks up the host | ||
95 | .Fa *ahost | ||
96 | using | ||
97 | .Xr getaddrinfo 3 | ||
98 | and, if the host exists, | ||
99 | .Fa *ahost | ||
100 | is set to the canonical name of the host. | ||
101 | A connection is then established to a server | ||
102 | residing at the well-known Internet port | ||
103 | .Fa inport . | ||
104 | If the user is not the superuser, the only valid port is | ||
105 | .Dq shell/tcp | ||
106 | (usually port 514). | ||
107 | .Pp | ||
108 | If the connection succeeds, | ||
109 | a socket in the Internet domain of type | ||
110 | .Dv SOCK_STREAM | ||
111 | is returned to the caller, and given to the remote | ||
112 | command as stdin and stdout. | ||
113 | If | ||
114 | .Fa fd2p | ||
115 | is non-zero, then an auxiliary channel to a control | ||
116 | process will be set up, and a descriptor for it will be placed | ||
117 | in | ||
118 | .Fa *fd2p . | ||
119 | The control process will return diagnostic | ||
120 | output from the command (unit 2) on this channel, and will also | ||
121 | accept bytes on this channel as being | ||
122 | .Tn UNIX | ||
123 | signal numbers, to be | ||
124 | forwarded to the process group of the command. | ||
125 | If | ||
126 | .Fa fd2p | ||
127 | is | ||
128 | .Va NULL , | ||
129 | then the standard error (unit 2 of the remote command) will be made | ||
130 | the same as the standard output and no provision is made for sending | ||
131 | arbitrary signals to the remote process, although you may be able to | ||
132 | get its attention by using out-of-band data. | ||
133 | Note that if the user is not the superuser, | ||
134 | .Fa fd2p | ||
135 | must be | ||
136 | .Va NULL . | ||
137 | .Pp | ||
138 | .Fn rcmd_af | ||
139 | takes address family in the last argument. | ||
140 | If the last argument is | ||
141 | .Dv AF_UNSPEC , | ||
142 | interpretation of | ||
143 | .Fa *ahost | ||
144 | will obey the underlying address resolution like DNS. | ||
145 | .Pp | ||
146 | The | ||
147 | .Fn rresvport | ||
148 | and | ||
149 | .Fn rresvport_af | ||
150 | functions are used to obtain a socket with a privileged | ||
151 | address bound to it. | ||
152 | This socket is suitable for use by | ||
153 | .Fn rcmd | ||
154 | and several other functions. | ||
155 | Privileged Internet ports are those in the range 0 to | ||
156 | .Va IPPORT_RESERVED - 1 , | ||
157 | which happens to be 1023. | ||
158 | Only the superuser is allowed to bind an address of this sort to a socket. | ||
159 | .Fn rresvport | ||
160 | and | ||
161 | .Fn rresvport_af | ||
162 | need to be seeded with a port number; if that port | ||
163 | is not available these functions will find another. | ||
164 | .Pp | ||
165 | The | ||
166 | .Fn ruserok | ||
167 | function takes a remote host's name, two user names, | ||
168 | and a flag indicating whether the local user's | ||
169 | name is that of the superuser. | ||
170 | Then, if the user is | ||
171 | .Em not | ||
172 | the superuser, it checks the | ||
173 | .Pa /etc/hosts.equiv | ||
174 | file. | ||
175 | If that lookup is not done, or is unsuccessful, the | ||
176 | .Pa .rhosts | ||
177 | in the local user's home directory is checked to see if the request for | ||
178 | service is allowed. | ||
179 | .Pp | ||
180 | If this file does not exist, is not a regular file, is owned by anyone | ||
181 | other than the user or the superuser, or is writeable by anyone other | ||
182 | than the owner, the check automatically fails. | ||
183 | Zero is returned if the machine name is listed in the | ||
184 | .Pa hosts.equiv | ||
185 | file, or the host and remote user name are found in the | ||
186 | .Pa .rhosts | ||
187 | file; otherwise | ||
188 | .Fn ruserok | ||
189 | returns \-1. | ||
190 | If the local domain (as obtained from | ||
191 | .Xr getaddrinfo 3 ) | ||
192 | is the same as the remote domain, only the machine name need be specified. | ||
193 | .Pp | ||
194 | .Fn ruserok | ||
195 | implicitly requires trusting the DNS server for the remote host's domain. | ||
196 | .Sh DIAGNOSTICS | ||
197 | The | ||
198 | .Fn rcmd | ||
199 | function returns a valid socket descriptor on success. | ||
200 | It returns \-1 on error and prints a diagnostic message on the standard error. | ||
201 | .Pp | ||
202 | The | ||
203 | .Fn rresvport | ||
204 | and | ||
205 | .Fn rresvport_af | ||
206 | functions return a valid, bound socket descriptor on success. | ||
207 | It returns \-1 on error with the global value | ||
208 | .Va errno | ||
209 | set according to the reason for failure. | ||
210 | The error code | ||
211 | .Er EAGAIN | ||
212 | is overloaded to mean | ||
213 | .Dq all network ports in use . | ||
214 | .Sh SEE ALSO | ||
215 | .Xr ssh 1 , | ||
216 | .Xr intro 2 , | ||
217 | .Xr bindresvport 3 , | ||
218 | .Xr bindresvport_sa 3 , | ||
219 | .Xr rcmdsh 3 | ||
220 | .Sh HISTORY | ||
221 | These | ||
222 | functions appeared in | ||
223 | .Bx 4.2 . | ||
224 | .Pp | ||
225 | The | ||
226 | .Fn iruserok | ||
227 | and | ||
228 | .Fn iruserok_sa | ||
229 | functions, IP address based versions of | ||
230 | .Fn ruserok , | ||
231 | were removed in | ||
232 | .Ox 6.0 . | ||