man3/rcmd.3

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  35 .\"
  36 .\"     @(#)rcmd.3      8.1 (Berkeley) 6/4/93
  37 .\"
  38 .\" Contributed as Linux man page by David A. Holland, 970908
  39 .\" I have not checked whether the Linux situation is exactly the same.
  40 .\"
  41 .\" 2007-12-08, mtk, Converted from mdoc to man macros
  42 .\"
  43 .TH RCMD 3 2017-09-15 "Linux" "Linux Programmer's Manual"
  44 .SH NAME
  45 rcmd, rresvport, iruserok, ruserok, rcmd_af,
  46 rresvport_af, iruserok_af, ruserok_af \- routines for returning a
  47 stream to a remote command
  48 .SH SYNOPSIS
  49 .nf
  50 .B #include <netdb.h> \ \ \fP/* Or <unistd.h> on some systems */
  51 .PP
  52 .BI "int rcmd(char **" ahost ", unsigned short " inport ", const char *" locuser ", "
  53 .BI "         const char *" remuser ", const char *" cmd ", int *" fd2p );
  54 .PP
  55 .BI "int rresvport(int *" port );
  56 .PP
  57 .BI "int iruserok(uint32_t " raddr ", int " superuser ", "
  58 .BI "             const char *" ruser ", const char *" luser );
  59 .PP
  60 .BI "int ruserok(const char *" rhost ", int " superuser ", "
  61 .BI "            const char *" ruser ", const char *" luser );
  62 .PP
  63 .BI "int rcmd_af(char **" ahost ", unsigned short " inport ", const char *" locuser ", "
  64 .BI "            const char *" remuser ", const char *" cmd ", int *" fd2p ,
  65 .BI "            sa_family_t " af );
  66 .PP
  67 .BI "int rresvport_af(int *" port ", sa_family_t " af );
  68 .PP
  69 .BI "int iruserok_af(const void *" raddr ", int " superuser ", "
  70 .BI "                const char *" ruser ", const char *" luser \
  71 ", sa_family_t " af );
  72 .PP
  73 .BI "int ruserok_af(const char *" rhost ", int " superuser ", "
  74 .BI "               const char *" ruser ", const char *" luser \
  75 ", sa_family_t " af );
  76 .fi
  77 .PP
  78 .in -4n
  79 Feature Test Macro Requirements for glibc (see
  80 .BR feature_test_macros (7)):
  81 .in
  82 .PP
  83 .BR rcmd (),
  84 .BR rcmd_af (),
  85 .BR rresvport (),
  86 .BR rresvport_af (),
  87 .BR iruserok (),
  88 .BR iruserok_af (),
  89 .BR ruserok (),
  90 .BR ruserok_af ():
  91     Since glibc 2.19:
  92         _DEFAULT_SOURCE
  93     Glibc 2.19 and earlier:
  94         _BSD_SOURCE
  95 .SH DESCRIPTION
  96 The
  97 .BR rcmd ()
  98 function is used by the superuser to execute a command on
  99 a remote machine using an authentication scheme based
 100 on privileged port numbers.
 101 The
 102 .BR rresvport ()
 103 function
 104 returns a file descriptor to a socket
 105 with an address in the privileged port space.
 106 The
 107 .BR iruserok ()
 108 and
 109 .BR ruserok ()
 110 functions are used by servers
 111 to authenticate clients requesting service with
 112 .BR rcmd ().
 113 All four functions are used by the
 114 .BR rshd (8)
 115 server (among others).
 116 .SS rcmd()
 117 .PP
 118 The
 119 .BR rcmd ()
 120 function
 121 looks up the host
 122 .I *ahost
 123 using
 124 .BR gethostbyname (3),
 125 returning \-1 if the host does not exist.
 126 Otherwise,
 127 .I *ahost
 128 is set to the standard name of the host
 129 and a connection is established to a server
 130 residing at the well-known Internet port
 131 .IR inport .
 132 .PP
 133 If the connection succeeds,
 134 a socket in the Internet domain of type
 135 .BR SOCK_STREAM
 136 is returned to the caller, and given to the remote
 137 command as
 138 .IR stdin
 139 and
 140 .IR stdout .
 141 If
 142 .I fd2p
 143 is nonzero, then an auxiliary channel to a control
 144 process will be set up, and a file descriptor for it will be placed
 145 in
 146 .IR *fd2p .
 147 The control process will return diagnostic
 148 output from the command (unit 2) on this channel, and will also
 149 accept bytes on this channel as being UNIX signal numbers, to be
 150 forwarded to the process group of the command.
 151 If
 152 .I fd2p
 153 is 0, then the
 154 .IR stderr
 155 (unit 2 of the remote
 156 command) will be made the same as the
 157 .IR stdout
 158 and no
 159 provision is made for sending arbitrary signals to the remote process,
 160 although you may be able to get its attention by using out-of-band data.
 161 .PP
 162 The protocol is described in detail in
 163 .BR rshd (8).
 164 .SS rresvport()
 165 .PP
 166 The
 167 .BR rresvport ()
 168 function is used to obtain a socket with a privileged
 169 port bound to it.
 170 This socket is suitable for use by
 171 .BR rcmd ()
 172 and several other functions.
 173 Privileged ports are those in the range 0 to 1023.
 174 Only a privileged process
 175 (on Linux: a process that has the
 176 .B CAP_NET_BIND_SERVICE
 177 capability in the user namespace governing its network namespace).
 178 is allowed to bind to a privileged port.
 179 In the glibc implementation,
 180 this function restricts its search to the ports from 512 to 1023.
 181 The
 182 .I port
 183 argument is value-result:
 184 the value it supplies to the call is used as the starting point
 185 for a circular search of the port range;
 186 on (successful) return, it contains the port number that was bound to.
 187 .\"
 188 .SS iruserok() and ruserok()
 189 .PP
 190 The
 191 .BR iruserok ()
 192 and
 193 .BR ruserok ()
 194 functions take a remote host's IP address or name, respectively,
 195 two usernames and a flag indicating whether the local user's
 196 name is that of the superuser.
 197 Then, if the user is
 198 .I not
 199 the superuser, it checks the
 200 .IR /etc/hosts.equiv
 201 file.
 202 If that lookup is not done, or is unsuccessful, the
 203 .IR .rhosts
 204 in the local user's home directory is checked to see if the request for
 205 service is allowed.
 206 .PP
 207 If this file does not exist, is not a regular file, is owned by anyone
 208 other than the user or the superuser, is writable by anyone other
 209 than the owner, or is hardlinked anywhere, the check automatically fails.
 210 Zero is returned if the machine name is listed in the
 211 .IR hosts.equiv
 212 file, or the host and remote username are found in the
 213 .IR .rhosts
 214 file; otherwise
 215 .BR iruserok ()
 216 and
 217 .BR ruserok ()
 218 return \-1.
 219 If the local domain (as obtained from
 220 .BR gethostname (2))
 221 is the same as the remote domain, only the machine name need be specified.
 222 .PP
 223 If the IP address of the remote host is known,
 224 .BR iruserok ()
 225 should be used in preference to
 226 .BR ruserok (),
 227 as it does not require trusting the DNS server for the remote host's domain.
 228 .SS *_af() variants
 229 All of the functions described above work with IPv4
 230 .RB ( AF_INET )
 231 sockets.
 232 The "_af" variants take an extra argument that allows the
 233 socket address family to be specified.
 234 For these functions, the
 235 .I af
 236 argument can be specified as
 237 .BR AF_INET
 238 or
 239 .BR AF_INET6 .
 240 In addition,
 241 .BR rcmd_af ()
 242 supports the use of
 243 .BR AF_UNSPEC .
 244 .SH RETURN VALUE
 245 The
 246 .BR rcmd ()
 247 function
 248 returns a valid socket descriptor on success.
 249 It returns \-1 on error and prints a diagnostic message on the standard error.
 250 .PP
 251 The
 252 .BR rresvport ()
 253 function
 254 returns a valid, bound socket descriptor on success.
 255 It returns \-1 on error with the global value
 256 .I errno
 257 set according to the reason for failure.
 258 The error code
 259 .BR EAGAIN
 260 is overloaded to mean "All network ports in use."
 261 .PP
 262 For information on the return from
 263 .BR ruserok ()
 264 and
 265 .BR iruserok (),
 266 see above.
 267 .SH VERSIONS
 268 The functions
 269 .BR iruserok_af (),
 270 .BR rcmd_af (),
 271 .BR rresvport_af (),
 272 and
 273 .BR ruserok_af ()
 274 functions are provide in glibc since version 2.2.
 275 .SH ATTRIBUTES
 276 For an explanation of the terms used in this section, see
 277 .BR attributes (7).
 278 .TS
 279 allbox;
 280 lbw27 lb lb
 281 l l l.
 282 Interface       Attribute       Value
 283 T{
 284 .BR rcmd (),
 285 .BR rcmd_af ()
 286 T}      Thread safety   MT-Unsafe
 287 T{
 288 .BR rresvport (),
 289 .BR rresvport_af ()
 290 T}      Thread safety   MT-Safe
 291 T{
 292 .BR iruserok (),
 293 .BR ruserok (),
 294 .br
 295 .BR iruserok_af (),
 296 .BR ruserok_af ()
 297 T}      Thread safety   MT-Safe locale
 298 .TE
 299 .sp 1
 300 .SH CONFORMING TO
 301 Not in POSIX.1.
 302 Present on the BSDs, Solaris, and many other systems.
 303 These
 304 functions appeared in
 305 4.2BSD.
 306 The "_af" variants are more recent additions,
 307 and are not present on as wide a range of systems.
 308 .SH BUGS
 309 .BR iruserok ()
 310 and
 311 .BR iruserok_af ()
 312 are declared in glibc headers only since version 2.12.
 313 .\" Bug filed 25 Nov 2007:
 314 .\" http://sources.redhat.com/bugzilla/show_bug.cgi?id=5399
 315 .SH SEE ALSO
 316 .BR rlogin (1),
 317 .BR rsh (1),
 318 .BR intro (2),
 319 .BR rexec (3),
 320 .BR rexecd (8),
 321 .BR rlogind (8),
 322 .BR rshd (8)