cnetdb(3) [debian man page]

CNETDB(3)						     Common Library Functions							 CNETDB(3)

NAME

       Cnetdb - LCG netdb utilities

SYNOPSIS

       #include <Cnetdb.h>

       char  *Cgetnetaddress(int  sock,  const	void *sa, size_t salen, int *skey, const char **numeric_out, const char **name_out, int flags, int
       cflags);

DESCRIPTION

       Cnetdb provides several	netdb  like  functions	including  Cgethostbyname,  Cgethostbyaddr,  Cgetservbyname,  Cgetnameinfo,  Cgetaddrinfo,
       Cgai_strerror  which  behave  in  a  somewhat similar way to their system netdb counterparts. In addition Cnetdb provides a function called
       Cgetnetaddress which is currently the only one documented here.

       Cgetnetaddress returns a DNS domain name (often called a hostname) given either a network socket, in which case the hostname corresponds to
       the  peer  address  of the socket, or a sockaddr structure. The name will be returned as a numeric IP address and/or optionaly a DNS domain
       name.

       Exactly one of either sock or sa must be specified, the other should be set to -1 or NULL respectively.	If  both  are  set  the  behaviour
       should  be  considered  undefined  and may change in the future. If skey is NULL the memory for pointers returned by Cgetnetaddress will be
       dynamically allocated and it is the responsibility of the caller to free them when done. If not NULL skey should point to an int  which	is
       initially  set  to  a value of -1. The memory used to store the results returned by Cgetnetaddress will be allocated internally and will be
       reused during subsequent calls to Cgetnetaddress from the same thread and that share the same value of skey.

       If numeric_out or name_out are not NULL the char pointer which they reference will be reset to a pointer to a character array containig the
       numeric	or  domain  name address to be returned by the function. The output will be NULL if the function is unable to find an IP or domain
       name.  flags accepts the same bitmaped flags that can be set for getnameinfo(). cflags accepts bitmaped flags which are unique  to  Cgetne-
       taddress.

       If  NI_NUMERICHOST is specified in flags no attempt is made to obtain a domain name. If NI_NAMEREQD is specified nothing is returned unless
       a domain name address can be determined. NI_NUMERICHOST and NI_NAMEREQD are mutually exclusive. Other flags options may	be  set  and  will
       have the effect described for getnameinfo().

       cflags may take the bitmaped flags CNA_WANTLOOPBACK, CNA_NOFWDLOOKUP and CNA_FWDLOOKUP.

       By  default  if	the  address  to  be  returned is determined to be the loopback address any domain name returned will be that of the local
       machine.  If CNA_WANTLOOPBACK is specified any domain name returned will be that associated  with  the  loopback  address,  usually  local-
       host.localdomain.

       A  forward  lookup  verification of the domain name may be optionally specified with the CNA_FWDLOOKUP flag.  The forward lookup means that
       one of the address to which a domain name resolves must match the address passed to Cgetnetaddress. If the match  failes  the  domain  name
       will  be  considered to not be available. By default, or if the option CNA_NOFWDLOOKUP is passed in cflags, the forward lookup check is not
       performed or required. The behavior if both CNA_FWDLOOKUP and CNA_NOFWDLOOKUP are specified is undefined.

RETURN VALUE

       Cgetnetaddress() returns a pointer to the domain name, if available, or otherwise to the numeric IP address, if available.  If  neither	is
       available NULL is returned.

SEE ALSO

       gethostbyname(3), gethostbyaddr(3), getservbyname(3), getnameinfo(3), getaddrinfo(3), gai_strerror(3)

AUTHOR

       LCG Grid Deployment Team  and DPM Team <hep-service-dpm@cern.ch>

LCG
							   $Date: 2008/02/13 17:29:10 $ 						 CNETDB(3)

GETNAMEINFO(3)						   BSD Library Functions 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, socklen_t hostlen, char *serv, socklen_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.

     If a link-layer address is passed to getnameinfo(), its ASCII representation will be stored in host.  The string pointed to by serv will be
     set to the empty string if non-NULL; flags will always be ignored.  This is intended as a replacement for the legacy link_ntoa(3) function.

     The sockaddr structure sa should point to either a sockaddr_in, sockaddr_in6 or sockaddr_dl structure (for IPv4, IPv6 or link-layer respec-
     tively) 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'ing 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 refer-
     ence 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");
		   /*NOTREACHED*/
	   }
	   printf("host=%s, serv=%s
", 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
", hbuf);

SEE ALSO

     gai_strerror(3), getaddrinfo(3), gethostbyaddr(3), getservbyport(3), inet_ntop(3), link_ntoa(3), resolver(3), hosts(5), resolv.conf(5),
     services(5), hostname(7), named(8)

     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.

STANDARDS

     The getnameinfo() function is defined by the IEEE Std 1003.1g-2000 (``POSIX.1'') 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;
	   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
");
			   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);
	   }

BSD
								 February 28, 2007							       BSD