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
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
cap_getaddrinfo
(),
and
cap_getnameinfo
(),
functions are preferred over the cap_gethostbyname
(),
cap_gethostbyname2
(), and
cap_gethostbyaddr
()
functions.The functions
cap_gethostbyname
(),
cap_gethostbyname2
(),
cep_gethostbyaddr
()
and cap_getnameinfo
() are respectively equivalent to
gethostbyname(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 service. 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
orNAME2ADDR
. TheADDR2NAME
means that reverse DNS lookups are allowed withcap_getnameinfo
() andcap_gethostbyaddr
() functions. In case when type is set toNAME2ADDR
the name resolution is allowed withcap_getaddrinfo
(),cap_gethostbyname
(), andcap_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@dawidek.net>
under sponsorship from the FreeBSD Foundation.
This manual page was written by
Mariusz Zaborski
<oshogbo@FreeBSD.org>.