| GETNAMEINFO(3) |
AerieBSD 1.0 Refernce Manual |
GETNAMEINFO(3) |
NAME
getnameinfo —
socket address structure to hostname and service name
SYNOPSIS
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
int
getnameinfo(const struct sockaddr *sa, socklen_t salen, char *host" \);
"size_t hostlen" "char *serv" "size_t servlen" "int flags"
DESCRIPTION
The
getnameinfo();
function is used to convert a
sockaddr
structure to a pair of host name and service strings.
It is a replacement for and provides more flexibility than the
gethostbyaddr(3)
and
getservbyport(3)
functions and is the converse of the
getaddrinfo(3)
function.
The
sockaddr
structure
sa
should point to either a
sockaddr_in
or
sockaddr_in6
structure (for IPv4 or IPv6 respectively) that is
salen
bytes long.
The host and service names associated with
sa
are stored in
host
and
serv
which have length parameters
hostlen
and
servlen.
The maximum value for
hostlen
is
NI_MAXHOST
and
the maximum value for
servlen
is
NI_MAXSERV,
as defined by
‹netdb.h›.
If a length parameter is zero, no string will be stored.
Otherwise, enough space must be provided to store the
host name or service string plus a byte for the NUL terminator.
The
flags
argument is formed by
OR
the following values:
- NI_NOFQDN
-
A fully qualified domain name is not required for local hosts.
The local part of the fully qualified domain name is returned instead.
- NI_NUMERICHOST
-
Return the address in numeric form, as if calling
inet_ntop(3),
instead of a host name.
- NI_NAMEREQD
-
A name is required.
If the host name cannot be found in DNS and this flag is set,
a non-zero error code is returned.
If the host name is not found and the flag is not set, the
address is returned in numeric form.
- NI_NUMERICSERV
-
The service name is returned as a digit string representing the port number.
- NI_DGRAM
-
Specifies that the service being looked up is a datagram
service, and causes
getservbyport(3)
to be called with a second argument of
“udp”
instead of its default of
“tcp”.
This is required for the few ports (512\-514) that have different services
for
UDP
and
TCP.
This implementation allows numeric IPv6 address notation with scope identifier,
as documented in chapter 11 of draft-ietf-ipv6-scoping-arch-02.txt.
IPv6 link-local address will appear as a string like
“fe80::1%ne0”.
Refer to
getaddrinfo(3)
for more information.
RETURN VALUES
getnameinfo();
returns zero on success or one of the error codes listed in
gai_strerror(3)
if an error occurs.
EXAMPLES
The following code tries to get a numeric host name, and service name,
for a given socket address.
Observe that there is no hardcoded reference to a particular address family.
struct sockaddr *sa; /* input */
char hbuf[NI_MAXHOST], sbuf[NI_MAXSERV];
if (getnameinfo(sa, sa->sa_len, hbuf, sizeof(hbuf), sbuf,
sizeof(sbuf), NI_NUMERICHOST | NI_NUMERICSERV))
errx(1, "could not get numeric hostname");
printf("host=%s, serv=%s\en", hbuf, sbuf);
The following version checks if the socket address has a reverse address mapping:
struct sockaddr *sa; /* input */
char hbuf[NI_MAXHOST];
if (getnameinfo(sa, sa->sa_len, hbuf, sizeof(hbuf), NULL, 0,
NI_NAMEREQD))
errx(1, "could not resolve hostname");
printf("host=%s\en", hbuf);
SEE ALSO
gai_strerror(3),
getaddrinfo(3),
gethostbyaddr(3),
getservbyport(3),
inet_ntop(3),
resolver(3),
hosts(5),
resolv.conf(5),
services(5),
hostname(7),
named(8)
.Rs
.%A R. Gilligan
.%A S. Thomson
.%A J. Bound
.%A W. Stevens
.%T Basic Socket Interface Extensions for IPv6
.%R RFC 2553
.%D March 1999
.Re
.Rs
.%A S. Deering
.%A B. Haberman
.%A T. Jinmei
.%A E. Nordmark
.%A B. Zill
.%T "IPv6 Scoped Address Architecture"
.%R internet draft
.%N draft-ietf-ipv6-scoping-arch-02.txt
.%O work in progress material
.Re
.Rs
.%A Craig Metz
.%T Protocol Independence Using the Sockets API
.%B "Proceedings of the Freenix Track: 2000 USENIX Annual Technical Conference"
.%D June 2000
.Re
STANDARDS
The
getnameinfo();
function is defined by the
draft specification and documented in
"RFC 2553",
“Basic Socket Interface Extensions for IPv6”.
CAVEATS
getnameinfo();
can return both numeric and FQDN forms of the address specified in
sa.
There is no return value that indicates whether the string returned in
host
is a result of binary to numeric-text translation (like
inet_ntop(3/)),
or is the result of a DNS reverse lookup.
Because of this, malicious parties could set up a PTR record as follows:
1.0.0.127.in-addr.arpa. IN PTR 10.1.1.1
and trick the caller of
getnameinfo();
into believing that
sa
is
10.1.1.1
when it is actually
127.0.0.1.
To prevent such attacks, the use of
NI_NAMEREQD
is recommended when the result of
getnameinfo();
is used
for access control purposes:
struct sockaddr *sa;
char addr[NI_MAXHOST];
struct addrinfo hints, *res;
int error;
error = getnameinfo(sa, sa->sa_len, addr, sizeof(addr),
NULL, 0, NI_NAMEREQD);
if (error == 0) {
memset(&hints, 0, sizeof(hints));
hints.ai_socktype = SOCK_DGRAM; /*dummy*/
hints.ai_flags = AI_NUMERICHOST;
if (getaddrinfo(addr, "0", &hints, &res) == 0) {
/* malicious PTR record */
freeaddrinfo(res);
printf("bogus PTR record\en");
return -1;
}
/* addr is FQDN as a result of PTR lookup */
} else {
/* addr is numeric string */
error = getnameinfo(sa, sa->sa_len, addr, sizeof(addr),
NULL, 0, NI_NUMERICHOST);
}
BUGS
The implementation of
getnameinfo();
is not thread-safe.
OpenBSD
intentionally uses a different
NI_MAXHOST
value from what
"RFC 2553"
suggests, to avoid buffer length handling mistakes.
| AerieBSD 1.0 Reference Manual |
May 26 2009 |
GETNAMEINFO(3) |