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CAP_DNS(3)		     Library Functions Manual		      CAP_DNS(3)

NAME
     cap_getaddrinfo,  cap_getnameinfo,  cap_gethostbyname,  cap_gethostbyname2,
     cap_gethostbyaddr, cap_dns_type_limit, cap_dns_family_limit -- library  for
     getting network host entry in capability mode

LIBRARY
     libcap_dns

SYNOPSIS
     #include <sys/nv.h>
     #include <libcasper.h>
     #include <casper/cap_dns.h>

     int
     cap_getaddrinfo(cap_channel_t *chan, const char *hostname,
	 const char *servname, const struct addrinfo *hints,
	 struct addrinfo **res);

     int
     cap_getnameinfo(cap_channel_t *chan, const struct sockaddr *sa,
	 socklen_t salen, char *host, size_t hostlen, char *serv,
	 size_t servlen, int flags);

     struct hostent *
     cap_gethostbyname(const cap_channel_t *chan, const char *name);

     struct hostent *
     cap_gethostbyname2(const cap_channel_t *chan, const char *name, int af);

     struct hostent *
     cap_gethostbyaddr(const cap_channel_t *chan, const void *addr,
	 socklen_t len, int af);

     int
     cap_dns_type_limit(cap_channel_t *chan, const char * const *types,
	 size_t ntypes);

     int
     cap_dns_family_limit(const cap_channel_t *chan, const int *families,
	 size_t nfamilies);

DESCRIPTION
     This  service  is	obsolete  and  cap_net(3)  should  be used instead.  The
     cap_getaddrinfo(), and cap_getnameinfo(), functions are preferred over  the
     cap_gethostbyname(),  cap_gethostbyname2(),  and  cap_gethostbyaddr() func-
     tions.

     The  functions  cap_gethostbyname(),   cap_gethostbyname2(),   cep_gethost-
     byaddr()  and  cap_getnameinfo()  are respectively equivalent to gethostby-
     name(3), gethostbyname2(3), gethostbyaddr(3) and getnameinfo(3) except that
     the connection to the system.dns service needs to be provided.

     The cap_dns_type_limit() function limits the functions allowed in the  ser-
     vice.   The  types  variable can be set to ADDR2NAME or NAME2ADDR.  See the
     "LIMITS" section for more details.  The ntpyes variable contains the number
     of types provided.

     The cap_dns_family_limit() functions allows to limit address families.  For
     details see "LIMITS".   The  nfamilies  variable  contains  the  number  of
     families provided.

LIMITS
     The  preferred way of setting limits is to use the cap_dns_type_limit() and
     cap_dns_family_limit() functions, but the limits of service can be set also
     using cap_limit_set(3).  The nvlist(9) for that function  can  contain  the
     following values and types:

	   type (NV_TYPE_STRING)
	   The	type can have two values: ADDR2NAME or NAME2ADDR.  The ADDR2NAME
	   means that reverse DNS lookups are allowed with cap_getnameinfo() and
	   cap_gethostbyaddr() functions.  In case when type is set to NAME2ADDR
	   the name resolution is allowed with cap_getaddrinfo(), cap_gethostby-
	   name(), and cap_gethostbyname2() functions.

	   family (NV_TYPE_NUMBER)
	   The family limits service  to  one  of  the	address  families  (e.g.
	   AF_INET, AF_INET6, etc.).

EXAMPLES
     The following example first opens a capability to casper and then uses this
     capability  to  create the system.dns casper service and uses it to resolve
     an IP address.

     cap_channel_t *capcas, *capdns;
     int familylimit, error;
     const char *ipstr = "127.0.0.1";
     const char *typelimit = "ADDR2NAME";
     char hname[NI_MAXHOST];
     struct addrinfo hints, *res;

     /* Open capability to Casper. */
     capcas = cap_init();
     if (capcas == NULL)
	     err(1, "Unable to contact Casper");

     /* Cache NLA for gai_strerror. */
     caph_cache_catpages();

     /* Enter capability mode sandbox. */
     if (caph_enter() < 0)
	     err(1, "Unable to enter capability mode");

     /* Use Casper capability to create capability to the system.dns service. */
     capdns = cap_service_open(capcas, "system.dns");
     if (capdns == NULL)
	     err(1, "Unable to open system.dns service");

     /* Close Casper capability, we don't need it anymore. */
     cap_close(capcas);

     /* Limit system.dns to reserve IPv4 addresses */
     familylimit = AF_INET;
     if (cap_dns_family_limit(capdns, &familylimit, 1) < 0)
	     err(1, "Unable to limit access to the system.dns service");

     /* Convert IP address in C-string to struct sockaddr. */
     memset(&hints, 0, sizeof(hints));
     hints.ai_family = familylimit;
     hints.ai_flags = AI_NUMERICHOST;
     error = cap_getaddrinfo(capdns, ipstr, NULL, &hints, &res);
     if (error != 0)
	    errx(1, "cap_getaddrinfo(): %s: %s", ipstr, gai_strerror(error));

     /* Limit system.dns to reverse DNS lookups. */
     if (cap_dns_type_limit(capdns, &typelimit, 1) < 0)
	     err(1, "Unable to limit access to the system.dns service");

     /* Find hostname for the given IP address. */
     error = cap_getnameinfo(capdns, res->ai_addr, res->ai_addrlen, hname, sizeof(hname),
	 NULL, 0, 0);
     if (error != 0)
	     errx(1, "cap_getnameinfo(): %s: %s", ipstr, gai_strerror(error));

     printf("Name associated with %s is %s.\n", ipstr, hname);

SEE ALSO
     cap_enter(2), caph_enter(3),  err(3),  gethostbyaddr(3),  gethostbyname(3),
     gethostbyname2(3), getnameinfo(3), capsicum(4), nv(9)

HISTORY
     The cap_dns service first appeared in FreeBSD 10.3.

AUTHORS
     The  cap_dns  service  was  implemented  by Pawel Jakub Dawidek <pawel@daw-
     idek.net> under sponsorship from the FreeBSD Foundation.

     This manual page was written by
     Mariusz Zaborski <oshogbo@FreeBSD.org>.

FreeBSD ports 15.1		 August 15, 2020		      CAP_DNS(3)

Want to link to this manual page? Use this URL:
<https://man.freebsd.org/cgi/man.cgi?query=cap_dns&sektion=3&manpath=FreeBSD+15.1-RELEASE+and+Ports>

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