1.\" Copyright (c) 2018 Mariusz Zaborski <oshogbo@FreeBSD.org>
2.\" All rights reserved.
3.\"
4.\" Redistribution and use in source and binary forms, with or without
5.\" modification, are permitted provided that the following conditions
6.\" are met:
7.\" 1. Redistributions of source code must retain the above copyright
8.\"    notice, this list of conditions and the following disclaimer.
9.\" 2. Redistributions in binary form must reproduce the above copyright
10.\"    notice, this list of conditions and the following disclaimer in the
11.\"    documentation and/or other materials provided with the distribution.
12.\"
13.\" THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND
14.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
15.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
16.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE
17.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
18.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
19.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
20.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
21.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
22.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
23.\" SUCH DAMAGE.
24.\"
25.\" $FreeBSD$
26.\"
27.Dd March 18, 2018
28.Dt CAP_DNS 3
29.Os
30.Sh NAME
31.Nm cap_gethostbyname ,
32.Nm cap_gethostbyname2 ,
33.Nm cap_gethostbyaddr ,
34.Nm cap_getnameinfo ,
35.Nm cap_dns_type_limit ,
36.Nm cap_dns_family_limit
37.Nd "library for getting network host entry in capability mode"
38.Sh LIBRARY
39.Lb libcap_dns
40.Sh SYNOPSIS
41.In sys/nv.h
42.In libcasper.h
43.In casper/cap_dns.h
44.Ft "struct hostent *"
45.Fn cap_gethostbyname "const cap_channel_t *chan" "const char *name"
46.Ft "struct hostent *"
47.Fn cap_gethostbyname2 "const cap_channel_t *chan" "const char *name" "int af"
48.Ft "struct hostent *"
49.Fn cap_gethostbyaddr "const cap_channel_t *chan" "const void *addr" "socklen_t len" "int af"
50.Ft "int"
51.Fn cap_getnameinfo "const cap_channel_t *chan" "const void *name" "int namelen"
52.Ft "int"
53.Fn cap_dns_type_limit "cap_channel_t *chan" "const char * const *types" "size_t ntypes"
54.Ft "int"
55.Fn cap_dns_family_limit "const cap_channel_t *chan" "const int *families" "size_t nfamilies"
56.Sh DESCRIPTION
57The functions
58.Fn cap_gethostbyname ,
59.Fn cap_gethostbyname2 ,
60.Fn cep_gethostbyaddr
61and
62.Fn cap_getnameinfo
63are respectively equivalent to
64.Xr gethostbyname 2 ,
65.Xr gethostbyname2 2 ,
66.Xr gethostbyaddr 2
67and
68.Xr getnameinfo 2
69except that the connection to the
70.Nm system.dns
71service needs to be provided.
72.Pp
73The
74.Fn cap_dns_type_limit
75function limits the functions allowed in the service.
76The
77.Fa types
78variable can be set to
79.Dv ADDR
80or
81.Dv NAME .
82See the
83.Sx LIMITS
84section for more details.
85The
86.Fa ntpyes
87variable contains the number of
88.Fa types
89provided.
90.Pp
91The
92.Fn cap_dns_family_limit
93functions allows to limit address families.
94For details see
95.Sx LIMITS .
96The
97.Fa nfamilies
98variable contains the number of
99.Fa families
100provided.
101.Sh LIMITS
102The preferred way of setting limits is to use the
103.Fn cap_dns_type_limit
104and
105.Fn cap_dns_family_limit
106functions, but the limits of service can be set also using
107.Xr cap_limit_set 3 .
108The
109.Xr nvlist 9
110for that function can contain the following values and types:
111.Bl -ohang -offset indent
112.It type ( NV_TYPE_STRING )
113The
114.Va type
115can have two values:
116.Dv ADDR
117or
118.Dv NAME .
119The
120.Dv ADDR
121means that functions
122.Fn cap_gethostbyname ,
123.Fn cap_gethostbyname2
124and
125.Fn cap_gethostbyaddr
126are allowed.
127In case when
128.Va type
129is set to
130.Dv NAME
131the
132.Fn cap_getnameinfo
133function is allowed.
134.It family ( NV_TYPE_NUMBER )
135The
136.Va family
137limits service to one of the address families (e.g.
138.Dv AF_INET , AF_INET6 ,
139etc.).
140.Sh EXAMPLES
141The following example first opens a capability to casper and then uses this
142capability to create the
143.Nm system.dns
144casper service and uses it to resolve an IP address.
145.Bd -literal
146cap_channel_t *capcas, *capdns;
147const char *typelimit = "ADDR";
148int familylimit;
149const char *ipstr = "127.0.0.1";
150struct in_addr ip;
151struct hostent *hp;
152
153/* Open capability to Casper. */
154capcas = cap_init();
155if (capcas == NULL)
156	err(1, "Unable to contact Casper");
157
158/* Enter capability mode sandbox. */
159if (cap_enter() < 0 && errno != ENOSYS)
160	err(1, "Unable to enter capability mode");
161
162/* Use Casper capability to create capability to the system.dns service. */
163capdns = cap_service_open(capcas, "system.dns");
164if (capdns == NULL)
165	err(1, "Unable to open system.dns service");
166
167/* Close Casper capability, we don't need it anymore. */
168cap_close(capcas);
169
170/* Limit system.dns to reverse DNS lookups. */
171if (cap_dns_type_limit(capdns, &typelimit, 1) < 0)
172	err(1, "Unable to limit access to the system.dns service");
173
174/* Limit system.dns to reserve IPv4 addresses */
175familylimit = AF_INET;
176if (cap_dns_family_limit(capdns, &familylimit, 1) < 0)
177	err(1, "Unable to limit access to the system.dns service");
178
179/* Convert IP address in C-string to in_addr. */
180if (!inet_aton(ipstr, &ip))
181	errx(1, "Unable to parse IP address %s.", ipstr);
182
183/* Find hostname for the given IP address. */
184hp = cap_gethostbyaddr(capdns, (const void *)&ip, sizeof(ip), AF_INET);
185if (hp == NULL)
186	errx(1, "No name associated with %s.", ipstr);
187
188printf("Name associated with %s is %s.\\n", ipstr, hp->h_name);
189.Ed
190.Sh SEE ALSO
191.Xr cap_enter 2 ,
192.Xr err 3 ,
193.Xr gethostbyaddr 3 ,
194.Xr gethostbyname 3 ,
195.Xr gethostbyname2 3 ,
196.Xr getnameinfo 3 ,
197.Xr capsicum 4 ,
198.Xr nv 9
199.Sh AUTHORS
200The
201.Nm cap_dns
202service was implemented by
203.An Pawel Jakub Dawidek Aq Mt pawel@dawidek.net
204under sponsorship from the FreeBSD Foundation.
205.Pp
206This manual page was written by
207.An Mariusz Zaborski Aq Mt oshogbo@FreeBSD.org .
208