286 lines
7.1 KiB
Groff
286 lines
7.1 KiB
Groff
.\" $KAME: getnameinfo.3,v 1.37 2005/01/05 03:23:05 itojun Exp $
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.\" $OpenBSD: getnameinfo.3,v 1.36 2004/12/21 09:48:20 jmc Exp $
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.\"
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.\" Copyright (C) 2004 Internet Systems Consortium, Inc. ("ISC")
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.\" Copyright (C) 2000, 2001 Internet Software Consortium.
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.\"
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.\" Permission to use, copy, modify, and distribute this software for any
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.\" purpose with or without fee is hereby granted, provided that the above
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.\" copyright notice and this permission notice appear in all copies.
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.\"
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.\" THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
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.\" REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
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.\" AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
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.\" INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
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.\" LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
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.\" OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
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.\" PERFORMANCE OF THIS SOFTWARE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd February 14, 2013
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.Dt GETNAMEINFO 3
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.Os
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.Sh NAME
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.Nm getnameinfo
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.Nd socket address structure to hostname and service name
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.Sh SYNOPSIS
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.In sys/types.h
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.In sys/socket.h
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.In netdb.h
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.Ft int
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.Fo getnameinfo
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.Fa "const struct sockaddr *sa" "socklen_t salen" "char *host"
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.Fa "size_t hostlen" "char *serv" "size_t servlen" "int flags"
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.Fc
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.Sh DESCRIPTION
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The
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.Fn getnameinfo
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function is used to convert a
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.Li sockaddr
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structure to a pair of host name and service strings.
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It is a replacement for and provides more flexibility than the
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.Xr gethostbyaddr 3
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and
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.Xr getservbyport 3
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functions and is the converse of the
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.Xr getaddrinfo 3
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function.
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.Pp
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If a link-layer address is passed to
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.Fn getnameinfo ,
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its ASCII representation will be stored in
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.Fa host .
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The string pointed to by
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.Fa serv
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will be set to the empty string if non-NULL;
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.Fa flags
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will always be ignored.
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This is intended as a replacement for the legacy
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.Xr link_ntoa 3
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function.
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.Pp
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The
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.Li sockaddr
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structure
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.Fa sa
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should point to either a
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.Li sockaddr_in ,
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.Li sockaddr_in6
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or
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.Li sockaddr_dl
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structure (for IPv4, IPv6 or link-layer respectively) that is
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.Fa salen
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bytes long.
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.Pp
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The host and service names associated with
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.Fa sa
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are stored in
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.Fa host
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and
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.Fa serv
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which have length parameters
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.Fa hostlen
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and
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.Fa servlen .
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The maximum value for
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.Fa hostlen
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is
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.Dv NI_MAXHOST
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and
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the maximum value for
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.Fa servlen
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is
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.Dv NI_MAXSERV ,
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as defined by
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.Aq Pa netdb.h .
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If a length parameter is zero, no string will be stored.
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Otherwise, enough space must be provided to store the
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host name or service string plus a byte for the NUL terminator.
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.Pp
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The
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.Fa flags
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argument is formed by
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.Tn OR Ns 'ing
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the following values:
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.Bl -tag -width "NI_NUMERICHOSTXX"
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.It Dv NI_NOFQDN
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A fully qualified domain name is not required for local hosts.
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The local part of the fully qualified domain name is returned instead.
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.It Dv NI_NUMERICHOST
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Return the address in numeric form, as if calling
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.Xr inet_ntop 3 ,
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instead of a host name.
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.It Dv NI_NAMEREQD
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A name is required.
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If the host name cannot be found in DNS and this flag is set,
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a non-zero error code is returned.
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If the host name is not found and the flag is not set, the
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address is returned in numeric form.
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.It NI_NUMERICSERV
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The service name is returned as a digit string representing the port number.
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.It NI_DGRAM
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Specifies that the service being looked up is a datagram
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service, and causes
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.Xr getservbyport 3
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to be called with a second argument of
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.Dq udp
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instead of its default of
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.Dq tcp .
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This is required for the few ports (512\-514) that have different services
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for
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.Tn UDP
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and
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.Tn TCP .
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.El
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.Pp
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This implementation allows numeric IPv6 address notation with scope identifier,
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as documented in chapter 11 of RFC 4007.
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IPv6 link-local address will appear as a string like
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.Dq Li fe80::1%ne0 .
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Refer to
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.Xr getaddrinfo 3
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for more information.
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.Sh RETURN VALUES
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.Fn getnameinfo
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returns zero on success or one of the error codes listed in
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.Xr gai_strerror 3
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if an error occurs.
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.Sh EXAMPLES
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The following code tries to get a numeric host name, and service name,
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for a given socket address.
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Observe that there is no hardcoded reference to a particular address family.
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.Bd -literal -offset indent
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struct sockaddr *sa; /* input */
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char hbuf[NI_MAXHOST], sbuf[NI_MAXSERV];
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if (getnameinfo(sa, sa->sa_len, hbuf, sizeof(hbuf), sbuf,
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sizeof(sbuf), NI_NUMERICHOST | NI_NUMERICSERV)) {
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errx(1, "could not get numeric hostname");
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/* NOTREACHED */
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}
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printf("host=%s, serv=%s\en", hbuf, sbuf);
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.Ed
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.Pp
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The following version checks if the socket address has a reverse address mapping:
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.Bd -literal -offset indent
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struct sockaddr *sa; /* input */
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char hbuf[NI_MAXHOST];
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if (getnameinfo(sa, sa->sa_len, hbuf, sizeof(hbuf), NULL, 0,
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NI_NAMEREQD)) {
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errx(1, "could not resolve hostname");
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/* NOTREACHED */
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}
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printf("host=%s\en", hbuf);
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.Ed
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.Sh SEE ALSO
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.Xr gai_strerror 3 ,
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.Xr getaddrinfo 3 ,
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.Xr gethostbyaddr 3 ,
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.Xr getservbyport 3 ,
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.Xr inet_ntop 3 ,
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.Xr link_ntoa 3 ,
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.Xr resolver 3 ,
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.Xr hosts 5 ,
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.Xr resolv.conf 5 ,
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.Xr services 5 ,
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.Xr hostname 7 ,
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.Xr named 8
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.Rs
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.%A R. Gilligan
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.%A S. Thomson
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.%A J. Bound
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.%A J. McCann
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.%A W. Stevens
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.%T Basic Socket Interface Extensions for IPv6
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.%R RFC 3493
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.%D February 2003
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.Re
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.Rs
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.%A S. Deering
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.%A B. Haberman
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.%A T. Jinmei
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.%A E. Nordmark
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.%A B. Zill
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.%T "IPv6 Scoped Address Architecture"
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.%R RFC 4007
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.%D March 2005
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.Re
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.Rs
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.%A Craig Metz
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.%T Protocol Independence Using the Sockets API
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.%B "Proceedings of the freenix track: 2000 USENIX annual technical conference"
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.%D June 2000
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.Re
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.Sh STANDARDS
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The
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.Fn getnameinfo
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function is defined by the
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.St -p1003.1-2004
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specification and documented in
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.Tn "RFC 3493" ,
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.Dq Basic Socket Interface Extensions for IPv6 .
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.Sh CAVEATS
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.Fn getnameinfo
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can return both numeric and FQDN forms of the address specified in
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.Fa sa .
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There is no return value that indicates whether the string returned in
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.Fa host
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is a result of binary to numeric-text translation (like
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.Xr inet_ntop 3 ) ,
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or is the result of a DNS reverse lookup.
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Because of this, malicious parties could set up a PTR record as follows:
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.Bd -literal -offset indent
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1.0.0.127.in-addr.arpa. IN PTR 10.1.1.1
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.Ed
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.Pp
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and trick the caller of
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.Fn getnameinfo
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into believing that
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.Fa sa
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is
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.Li 10.1.1.1
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when it is actually
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.Li 127.0.0.1 .
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.Pp
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To prevent such attacks, the use of
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.Dv NI_NAMEREQD
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is recommended when the result of
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.Fn getnameinfo
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is used
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for access control purposes:
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.Bd -literal -offset indent
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struct sockaddr *sa;
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socklen_t salen;
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char addr[NI_MAXHOST];
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struct addrinfo hints, *res;
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int error;
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error = getnameinfo(sa, salen, addr, sizeof(addr),
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NULL, 0, NI_NAMEREQD);
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if (error == 0) {
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memset(&hints, 0, sizeof(hints));
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hints.ai_socktype = SOCK_DGRAM; /*dummy*/
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hints.ai_flags = AI_NUMERICHOST;
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if (getaddrinfo(addr, "0", &hints, &res) == 0) {
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/* malicious PTR record */
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freeaddrinfo(res);
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printf("bogus PTR record\en");
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return -1;
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}
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/* addr is FQDN as a result of PTR lookup */
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} else {
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/* addr is numeric string */
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error = getnameinfo(sa, salen, addr, sizeof(addr),
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NULL, 0, NI_NUMERICHOST);
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}
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.Ed
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.\".Pp
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.\".Ox
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.\"intentionally uses a different
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.\".Dv NI_MAXHOST
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.\"value from what
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.\".Tn "RFC 2553"
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.\"suggests, to avoid buffer length handling mistakes.
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