man3/rcmd.3

   1 .\"     $NetBSD: rcmd.3,v 1.9 1996/05/28 02:07:39 mrg Exp $
   2 .\"
   3 .\" Copyright (c) 1983, 1991, 1993
   4 .\"     The Regents of the University of California.  All rights reserved.
   5 .\"
   6 .\" SPDX-License-Identifier: BSD-4-Clause-UC
   7 .\"
   8 .\"     @(#)rcmd.3      8.1 (Berkeley) 6/4/93
   9 .\"
  10 .\" Contributed as Linux man page by David A. Holland, 970908
  11 .\" I have not checked whether the Linux situation is exactly the same.
  12 .\"
  13 .\" 2007-12-08, mtk, Converted from mdoc to man macros
  14 .\"
  15 .TH RCMD 3 2021-03-22 "Linux" "Linux Programmer's Manual"
  16 .SH NAME
  17 rcmd, rresvport, iruserok, ruserok, rcmd_af,
  18 rresvport_af, iruserok_af, ruserok_af \- routines for returning a
  19 stream to a remote command
  20 .SH LIBRARY
  21 Standard C library
  22 .RI ( libc ", " \-lc )
  23 .SH SYNOPSIS
  24 .nf
  25 .BR "#include <netdb.h>    " "/* Or <unistd.h> on some systems */"
  26 .PP
  27 .BI "int rcmd(char **restrict " ahost ", unsigned short " inport ,
  28 .BI "            const char *restrict " locuser ,
  29 .BI "            const char *restrict " remuser ,
  30 .BI "            const char *restrict " cmd ", int *restrict " fd2p );
  31 .PP
  32 .BI "int rresvport(int *" port );
  33 .PP
  34 .BI "int iruserok(uint32_t " raddr ", int " superuser ,
  35 .BI "            const char *" ruser ", const char *" luser );
  36 .BI "int ruserok(const char *" rhost ", int " superuser ,
  37 .BI "            const char *" ruser ", const char *" luser );
  38 .PP
  39 .BI "int rcmd_af(char **restrict " ahost ", unsigned short " inport ,
  40 .BI "            const char *restrict " locuser ,
  41 .BI "            const char *restrict " remuser ,
  42 .BI "            const char *restrict " cmd ", int *restrict " fd2p ,
  43 .BI "            sa_family_t " af );
  44 .PP
  45 .BI "int rresvport_af(int *" port ", sa_family_t " af );
  46 .PP
  47 .BI "int iruserok_af(const void *restrict " raddr ", int " superuser ,
  48 .BI "            const char *restrict " ruser ", const char *restrict " luser ,
  49 .BI "            sa_family_t " af );
  50 .BI "int ruserok_af(const char *" rhost ", int " superuser ,
  51 .BI "            const char *" ruser ", const char *" luser ,
  52 .BI "            sa_family_t " af );
  53 .fi
  54 .PP
  55 .RS -4
  56 Feature Test Macro Requirements for glibc (see
  57 .BR feature_test_macros (7)):
  58 .RE
  59 .ad l
  60 .PP
  61 .BR rcmd (),
  62 .BR rcmd_af (),
  63 .BR rresvport (),
  64 .BR rresvport_af (),
  65 .BR iruserok (),
  66 .BR iruserok_af (),
  67 .BR ruserok (),
  68 .BR ruserok_af ():
  69 .nf
  70     Since glibc 2.19:
  71         _DEFAULT_SOURCE
  72     Glibc 2.19 and earlier:
  73         _BSD_SOURCE
  74 .fi
  75 .ad
  76 .SH DESCRIPTION
  77 The
  78 .BR rcmd ()
  79 function is used by the superuser to execute a command on
  80 a remote machine using an authentication scheme based
  81 on privileged port numbers.
  82 The
  83 .BR rresvport ()
  84 function
  85 returns a file descriptor to a socket
  86 with an address in the privileged port space.
  87 The
  88 .BR iruserok ()
  89 and
  90 .BR ruserok ()
  91 functions are used by servers
  92 to authenticate clients requesting service with
  93 .BR rcmd ().
  94 All four functions are used by the
  95 .BR rshd (8)
  96 server (among others).
  97 .SS rcmd()
  98 The
  99 .BR rcmd ()
 100 function
 101 looks up the host
 102 .I *ahost
 103 using
 104 .BR gethostbyname (3),
 105 returning \-1 if the host does not exist.
 106 Otherwise,
 107 .I *ahost
 108 is set to the standard name of the host
 109 and a connection is established to a server
 110 residing at the well-known Internet port
 111 .IR inport .
 112 .PP
 113 If the connection succeeds,
 114 a socket in the Internet domain of type
 115 .BR SOCK_STREAM
 116 is returned to the caller, and given to the remote
 117 command as
 118 .IR stdin
 119 and
 120 .IR stdout .
 121 If
 122 .I fd2p
 123 is nonzero, then an auxiliary channel to a control
 124 process will be set up, and a file descriptor for it will be placed
 125 in
 126 .IR *fd2p .
 127 The control process will return diagnostic
 128 output from the command (unit 2) on this channel, and will also
 129 accept bytes on this channel as being UNIX signal numbers, to be
 130 forwarded to the process group of the command.
 131 If
 132 .I fd2p
 133 is 0, then the
 134 .IR stderr
 135 (unit 2 of the remote
 136 command) will be made the same as the
 137 .IR stdout
 138 and no
 139 provision is made for sending arbitrary signals to the remote process,
 140 although you may be able to get its attention by using out-of-band data.
 141 .PP
 142 The protocol is described in detail in
 143 .BR rshd (8).
 144 .SS rresvport()
 145 The
 146 .BR rresvport ()
 147 function is used to obtain a socket with a privileged
 148 port bound to it.
 149 This socket is suitable for use by
 150 .BR rcmd ()
 151 and several other functions.
 152 Privileged ports are those in the range 0 to 1023.
 153 Only a privileged process
 154 (on Linux, a process that has the
 155 .B CAP_NET_BIND_SERVICE
 156 capability in the user namespace governing its network namespace)
 157 is allowed to bind to a privileged port.
 158 In the glibc implementation,
 159 this function restricts its search to the ports from 512 to 1023.
 160 The
 161 .I port
 162 argument is value-result:
 163 the value it supplies to the call is used as the starting point
 164 for a circular search of the port range;
 165 on (successful) return, it contains the port number that was bound to.
 166 .\"
 167 .SS iruserok() and ruserok()
 168 The
 169 .BR iruserok ()
 170 and
 171 .BR ruserok ()
 172 functions take a remote host's IP address or name, respectively,
 173 two usernames and a flag indicating whether the local user's
 174 name is that of the superuser.
 175 Then, if the user is
 176 .I not
 177 the superuser, it checks the
 178 .IR /etc/hosts.equiv
 179 file.
 180 If that lookup is not done, or is unsuccessful, the
 181 .IR .rhosts
 182 in the local user's home directory is checked to see if the request for
 183 service is allowed.
 184 .PP
 185 If this file does not exist, is not a regular file, is owned by anyone
 186 other than the user or the superuser, is writable by anyone other
 187 than the owner, or is hardlinked anywhere, the check automatically fails.
 188 Zero is returned if the machine name is listed in the
 189 .IR hosts.equiv
 190 file, or the host and remote username are found in the
 191 .IR .rhosts
 192 file; otherwise
 193 .BR iruserok ()
 194 and
 195 .BR ruserok ()
 196 return \-1.
 197 If the local domain (as obtained from
 198 .BR gethostname (2))
 199 is the same as the remote domain, only the machine name need be specified.
 200 .PP
 201 If the IP address of the remote host is known,
 202 .BR iruserok ()
 203 should be used in preference to
 204 .BR ruserok (),
 205 as it does not require trusting the DNS server for the remote host's domain.
 206 .SS *_af() variants
 207 All of the functions described above work with IPv4
 208 .RB ( AF_INET )
 209 sockets.
 210 The "_af" variants take an extra argument that allows the
 211 socket address family to be specified.
 212 For these functions, the
 213 .I af
 214 argument can be specified as
 215 .BR AF_INET
 216 or
 217 .BR AF_INET6 .
 218 In addition,
 219 .BR rcmd_af ()
 220 supports the use of
 221 .BR AF_UNSPEC .
 222 .SH RETURN VALUE
 223 The
 224 .BR rcmd ()
 225 function
 226 returns a valid socket descriptor on success.
 227 It returns \-1 on error and prints a diagnostic message on the standard error.
 228 .PP
 229 The
 230 .BR rresvport ()
 231 function
 232 returns a valid, bound socket descriptor on success.
 233 On failure, it returns \-1 and sets
 234 .I errno
 235 to indicate the error.
 236 The error code
 237 .BR EAGAIN
 238 is overloaded to mean: "All network ports in use".
 239 .PP
 240 For information on the return from
 241 .BR ruserok ()
 242 and
 243 .BR iruserok (),
 244 see above.
 245 .SH VERSIONS
 246 The functions
 247 .BR iruserok_af (),
 248 .BR rcmd_af (),
 249 .BR rresvport_af (),
 250 and
 251 .BR ruserok_af ()
 252 functions are provide in glibc since version 2.2.
 253 .SH ATTRIBUTES
 254 For an explanation of the terms used in this section, see
 255 .BR attributes (7).
 256 .ad l
 257 .nh
 258 .TS
 259 allbox;
 260 lbx lb lb
 261 l l l.
 262 Interface       Attribute       Value
 263 T{
 264 .BR rcmd (),
 265 .BR rcmd_af ()
 266 T}      Thread safety   MT-Unsafe
 267 T{
 268 .BR rresvport (),
 269 .BR rresvport_af ()
 270 T}      Thread safety   MT-Safe
 271 T{
 272 .BR iruserok (),
 273 .BR ruserok (),
 274 .BR iruserok_af (),
 275 .BR ruserok_af ()
 276 T}      Thread safety   MT-Safe locale
 277 .TE
 278 .hy
 279 .ad
 280 .sp 1
 281 .SH CONFORMING TO
 282 Not in POSIX.1.
 283 Present on the BSDs, Solaris, and many other systems.
 284 These
 285 functions appeared in
 286 4.2BSD.
 287 The "_af" variants are more recent additions,
 288 and are not present on as wide a range of systems.
 289 .SH BUGS
 290 .BR iruserok ()
 291 and
 292 .BR iruserok_af ()
 293 are declared in glibc headers only since version 2.12.
 294 .\" Bug filed 25 Nov 2007:
 295 .\" http://sources.redhat.com/bugzilla/show_bug.cgi?id=5399
 296 .SH SEE ALSO
 297 .BR rlogin (1),
 298 .BR rsh (1),
 299 .BR rexec (3),
 300 .BR rexecd (8),
 301 .BR rlogind (8),
 302 .BR rshd (8)