GETNAMEINFO(3) | Library Functions Manual | GETNAMEINFO(3) |
getnameinfo
—
#include <netdb.h>
int
getnameinfo
(const
struct sockaddr * restrict sa,
socklen_t salen,
char * restrict host,
socklen_t hostlen,
char * restrict serv,
socklen_t servlen,
int flags);
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 a
sockaddr_in
(for IPv4),
sockaddr_in6
(for IPv6),
sockaddr_atalk
(for AppleTalk),
sockaddr_link
(for link layer), or
sockaddr_local
(for local/unix) structures that are
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'ing the following values:
NI_NOFQDN
NI_NUMERICHOST
NI_NAMEREQD
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.
getnameinfo
() returns zero on success or one of the
error codes listed in
gai_strerror(3) if an
error occurs.
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"); /*NOTREACHED*/ } printf("host=%s, serv=%s\n", 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"); /*NOTREACHED*/ } printf("host=%s\n", hbuf);
R. Gilligan, S. Thomson, J. Bound, and W. Stevens, Basic Socket Interface Extensions for IPv6, RFC 2553, March 1999.
S. Deering, B. Haberman, T. Jinmei, E. Nordmark, and B. Zill, IPv6 Scoped Address Architecture, internet draft, draft-ietf-ipv6-scoping-arch-02.txt, work in progress material.
Craig Metz, Protocol Independence Using the Sockets API, Proceedings of the FREENIX track: 2000 USENIX annual technical conference, June 2000.
getnameinfo
() function is defined by the
IEEE Std 1003.1g-2000 (“POSIX.1g”) draft
specification and documented in RFC 2553, “Basic
Socket Interface Extensions for IPv6”.
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; socklen_t salen; char addr[NI_MAXHOST]; struct addrinfo hints, *res; int error; error = getnameinfo(sa, salen, 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\n"); return -1; } /* addr is FQDN as a result of PTR lookup */ } else { /* addr is numeric string */ error = getnameinfo(sa, salen, addr, sizeof(addr), NULL, 0, NI_NUMERICHOST); }
August 18, 2013 | NetBSD 9.0 |