CAP_NET(3)

NAME
cap_bind, cap_connect, cap_getaddrinfo, cap_gethostbyaddr, cap_gethostbyname, cap_gethostbyname2, cap_getnameinfo, cap_net_free, cap_net_limit, cap_net_limit_addr2name, cap_net_limit_addr2name_family, cap_net_limit_bind, cap_net_limit_connect, cap_net_limit_init, cap_net_limit_name2addr, cap_net_limit_name2addr_family, - library for networking in capability mode

LIBRARY
libcap_net

SYNOPSIS
#include <sys/nv.h>
#include <libcasper.h>
#include <casper/cap_net.h>
int
cap_bind(cap_channel_t *chan, int s, const struct sockaddr *addr, socklen_t addrlen);
int
cap_connect(cap_channel_t *chan, int s, const struct sockaddr *name, socklen_t namelen);
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);
cap_net_limit_t *
cap_net_limit_init(cap_channel_t *chan, uint64_t mode);
int
cap_net_limit(cap_net_limit_t *limit);
void
cap_net_free(cap_net_limit_t *limit);
cap_net_limit_t *
cap_net_limit_addr2name_family(cap_net_limit_t *limit, int *family, size_t size);
cap_net_limit_t *
cap_net_limit_addr2name(cap_net_limit_t *limit, const struct sockaddr *sa, socklen_t salen);
cap_net_limit_t *
cap_net_limit_name2addr_family(cap_net_limit_t *limit, int *family, size_t size);
cap_net_limit_t *
cap_net_limit_name2addr(cap_net_limit_t *limit, const char *name, const char *serv);
cap_net_limit_t *
cap_net_limit_connect(cap_net_limit_t *limit, const struct sockaddr *sa, socklen_t salen);
cap_net_limit_t *
cap_net_limit_bind(cap_net_limit_t *limit, const struct sockaddr *sa, socklen_t salen);

DESCRIPTION
The functions cap_bind(), cap_connect(), cap_gethostbyname(), cap_gethostbyname2(), cap_gethostbyaddr() and cap_getnameinfo() provide a set of APIs equivalent to bind(2), connect(2), gethostbyname(3), gethostbyname2(3), gethostbyaddr(3) and getnameinfo(3) except that a connection to the system.net service needs to be provided.

LIMITS
By default, the cap_net capability provides unrestricted access to the network namespace. Applications typically only require access to a small portion of the network namespace: The cap_net_limit() function can be used to restrict access to the network. The cap_net_limit_init() returns an opaque limit handle used to store a list of capabilities. The restricts the functionality of the service. Modes are encoded using the following flags:

    CAPNET_ADDR2NAME		reverse DNS lookups are allowed with
    				cap_getnameinfo
    CAPNET_NAME2ADDR		name resolution is allowed with
    				cap_getaddrinfo
    CAPNET_DEPRECATED_ADDR2NAME	reverse DNS lookups are allowed with
    				cap_gethostbyaddr
    CAPNET_DEPRECATED_NAME2ADDR	name resolution is allowed with
    				cap_gethostbyname and cap_gethostbyname2
    CAPNET_BIND			bind syscall is allowed
    CAPNET_CONNECT			connect syscall is allowed
    CAPNET_CONNECTDNS		connect syscall is allowed to the values
    				returned from privies call to
    				the cap_getaddrinfo or cap_gethostbyname

cap_net_limit_addr2name_family() limits the cap_getnameinfo() and cap_gethostbyaddr() to do reverse DNS lookups to specific family (AF_INET, AF_INET6, etc.)

cap_net_limit_addr2name() limits the cap_getnameinfo() and cap_gethostbyaddr() to do reverse DNS lookups only on those specific structures.

cap_net_limit_name2addr_family() limits the cap_getaddrinfo(), cap_gethostbyname() and cap_gethostbyname2() to do the name resolution on specific family (AF_INET, AF_INET6, etc.)

cap_net_limit_addr2name() restricts cap_getaddrinfo(), cap_gethostbyname() and cap_gethostbyname2() to a set of domains.

cap_net_limit_bind() limits cap_bind() to bind only on those specific structures.

cap_net_limit_connect() limits cap_connect() to connect only on those specific structures. If the CAPNET_CONNECTDNS is set the limits are extended to the values returned by cap_getaddrinfo(), cap_gethostbyname() and cap_gethostbyname2() In case of the cap_getaddrinfo() the restriction is strict. In case of the cap_gethostbyname() and cap_gethostbyname2() any port will be accepted in the cap_connect() function.

cap_net_limit() applies a set of sysctl limits to the capability, denying access to sysctl variables not belonging to the set.

Once a set of limits is applied, subsequent calls to cap_net_limit() will fail unless the new set is a subset of the current set.

The cap_net_limit() will consume the limits. If the cap_net_limit() was not called the rights may be freed using cap_net_free(). Multiple calls to cap_net_limit_addr2name_family(), cap_net_limit_addr2name(), cap_net_limit_name2addr_family(), cap_net_limit_name2addr(), cap_net_limit_connect(), and cap_net_limit_bind() is supported, each call is extending preview capabilities.

EXAMPLES
The following example first opens a capability to casper and then uses this capability to create the system.net casper service and uses it to resolve a host and connect to it.

    cap_channel_t *capcas, *capnet;
    cap_net_limit_t *limit;
    int familylimit, error, s;
    const char *host = "example.com";
    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_casper() < 0)
    	err(1, "Unable to enter capability mode");
    /* Use Casper capability to create capability to the system.net service. */
    capnet = cap_service_open(capcas, "system.net");
    if (capnet == NULL)
    	err(1, "Unable to open system.net service");
    /* Close Casper capability. */
    cap_close(capcas);
    /* Limit system.net to reserve IPv4 addresses, to host example.com . */
    limit = cap_net_limit_init(capnet, CAPNET_NAME2ADDR | CAPNET_CONNECTDNS);
    if (limit == NULL)
    	err(1, "Unable to create limits.");
    cap_net_limit_name2addr(limit, host, "80");
    familylimit = AF_INET;
    cap_net_limit_name2addr_family(limit, &familylimit, 1);
    if (cap_net_limit(limit) < 0)
    	err(1, "Unable to apply limits.");
    /* Find IP addresses for the given host. */
    memset(&hints, 0, sizeof(hints));
    hints.ai_family = AF_INET;
    hints.ai_socktype = SOCK_STREAM;
    error = cap_getaddrinfo(capnet, host, "80", &hints, &res);
    if (error != 0)
    	errx(1, "cap_getaddrinfo(): %s: %s", host, gai_strerror(error));
    s = socket(res->ai_family, res->ai_socktype, res->ai_protocol);
    if (s < 0)
    	err(1, "Unable to create socket");
    if (cap_connect(capnet, s, res->ai_addr,  res->ai_addrlen) < 0)
    	err(1, "Unable to connect to host");

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

AUTHORS
Mariusz Zaborski <oshogbo@FreeBSD.org>