blob: d6242251b914f89270d53da63bac82c32b57fa04 [file] [log] [blame]
/* dnsmasq is Copyright (c) 2000-2016 Simon Kelley
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; version 2 dated June, 1991, or
(at your option) version 3 dated 29 June, 2007.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include "dnsmasq.h"
unsigned char *find_pseudoheader(struct dns_header *header, size_t plen, size_t *len, unsigned char **p, int *is_sign, int *is_last)
{
/* See if packet has an RFC2671 pseudoheader, and if so return a pointer to it.
also return length of pseudoheader in *len and pointer to the UDP size in *p
Finally, check to see if a packet is signed. If it is we cannot change a single bit before
forwarding. We look for TSIG in the addition section, and TKEY queries (for GSS-TSIG) */
int i, arcount = ntohs(header->arcount);
unsigned char *ansp = (unsigned char *)(header+1);
unsigned short rdlen, type, class;
unsigned char *ret = NULL;
if (is_sign)
{
*is_sign = 0;
if (OPCODE(header) == QUERY)
{
for (i = ntohs(header->qdcount); i != 0; i--)
{
if (!(ansp = skip_name(ansp, header, plen, 4)))
return NULL;
GETSHORT(type, ansp);
GETSHORT(class, ansp);
if (class == C_IN && type == T_TKEY)
*is_sign = 1;
}
}
}
else
{
if (!(ansp = skip_questions(header, plen)))
return NULL;
}
if (arcount == 0)
return NULL;
if (!(ansp = skip_section(ansp, ntohs(header->ancount) + ntohs(header->nscount), header, plen)))
return NULL;
for (i = 0; i < arcount; i++)
{
unsigned char *save, *start = ansp;
if (!(ansp = skip_name(ansp, header, plen, 10)))
return NULL;
GETSHORT(type, ansp);
save = ansp;
GETSHORT(class, ansp);
ansp += 4; /* TTL */
GETSHORT(rdlen, ansp);
if (!ADD_RDLEN(header, ansp, plen, rdlen))
return NULL;
if (type == T_OPT)
{
if (len)
*len = ansp - start;
if (p)
*p = save;
if (is_last)
*is_last = (i == arcount-1);
ret = start;
}
else if (is_sign &&
i == arcount - 1 &&
class == C_ANY &&
type == T_TSIG)
*is_sign = 1;
}
return ret;
}
/* replace == 2 ->delete existing option only. */
size_t add_pseudoheader(struct dns_header *header, size_t plen, unsigned char *limit,
unsigned short udp_sz, int optno, unsigned char *opt, size_t optlen, int set_do, int replace)
{
unsigned char *lenp, *datap, *p, *udp_len, *buff = NULL;
int rdlen = 0, is_sign, is_last;
unsigned short flags = set_do ? 0x8000 : 0, rcode = 0;
p = find_pseudoheader(header, plen, NULL, &udp_len, &is_sign, &is_last);
if (is_sign)
return plen;
if (p)
{
/* Existing header */
int i;
unsigned short code, len;
p = udp_len;
GETSHORT(udp_sz, p);
GETSHORT(rcode, p);
GETSHORT(flags, p);
if (set_do)
{
p -= 2;
flags |= 0x8000;
PUTSHORT(flags, p);
}
lenp = p;
GETSHORT(rdlen, p);
if (!CHECK_LEN(header, p, plen, rdlen))
return plen; /* bad packet */
datap = p;
/* no option to add */
if (optno == 0)
return plen;
/* check if option already there */
for (i = 0; i + 4 < rdlen;)
{
GETSHORT(code, p);
GETSHORT(len, p);
/* malformed option, delete the whole OPT RR and start again. */
if (i + len > rdlen)
{
rdlen = 0;
is_last = 0;
break;
}
if (code == optno)
{
if (replace == 0)
return plen;
/* delete option if we're to replace it. */
p -= 4;
rdlen -= len + 4;
memcpy(p, p+len+4, rdlen - i);
PUTSHORT(rdlen, lenp);
lenp -= 2;
}
else
{
p += len;
i += len + 4;
}
}
/* If we're going to extend the RR, it has to be the last RR in the packet */
if (!is_last)
{
/* First, take a copy of the options. */
if (rdlen != 0 && (buff = whine_malloc(rdlen)))
memcpy(buff, datap, rdlen);
/* now, delete OPT RR */
plen = rrfilter(header, plen, 0);
/* Now, force addition of a new one */
p = NULL;
}
}
if (!p)
{
/* We are (re)adding the pseudoheader */
if (!(p = skip_questions(header, plen)) ||
!(p = skip_section(p,
ntohs(header->ancount) + ntohs(header->nscount) + ntohs(header->arcount),
header, plen)))
return plen;
*p++ = 0; /* empty name */
PUTSHORT(T_OPT, p);
PUTSHORT(udp_sz, p); /* max packet length, 512 if not given in EDNS0 header */
PUTSHORT(rcode, p); /* extended RCODE and version */
PUTSHORT(flags, p); /* DO flag */
lenp = p;
PUTSHORT(rdlen, p); /* RDLEN */
datap = p;
/* Copy back any options */
if (buff)
{
memcpy(p, buff, rdlen);
free(buff);
p += rdlen;
}
header->arcount = htons(ntohs(header->arcount) + 1);
}
if (((ssize_t)optlen) > (limit - (p + 4)))
return plen; /* Too big */
/* Add new option */
if (optno != 0 && replace != 2)
{
PUTSHORT(optno, p);
PUTSHORT(optlen, p);
memcpy(p, opt, optlen);
p += optlen;
PUTSHORT(p - datap, lenp);
}
return p - (unsigned char *)header;
}
size_t add_do_bit(struct dns_header *header, size_t plen, unsigned char *limit)
{
return add_pseudoheader(header, plen, (unsigned char *)limit, PACKETSZ, 0, NULL, 0, 1, 0);
}
static unsigned char char64(unsigned char c)
{
return "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"[c & 0x3f];
}
static void encoder(unsigned char *in, char *out)
{
out[0] = char64(in[0]>>2);
out[1] = char64((in[0]<<4) | (in[1]>>4));
out[2] = char64((in[1]<<2) | (in[2]>>6));
out[3] = char64(in[2]);
}
static size_t add_dns_client(struct dns_header *header, size_t plen, unsigned char *limit, union mysockaddr *l3, time_t now)
{
int maclen, replace = 2; /* can't get mac address, just delete any incoming. */
unsigned char mac[DHCP_CHADDR_MAX];
char encode[18]; /* handle 6 byte MACs */
if ((maclen = find_mac(l3, mac, 1, now)) == 6)
{
replace = 1;
if (option_bool(OPT_MAC_HEX))
print_mac(encode, mac, maclen);
else
{
encoder(mac, encode);
encoder(mac+3, encode+4);
encode[8] = 0;
}
}
return add_pseudoheader(header, plen, limit, PACKETSZ, EDNS0_OPTION_NOMDEVICEID, (unsigned char *)encode, strlen(encode), 0, replace);
}
static size_t add_mac(struct dns_header *header, size_t plen, unsigned char *limit, union mysockaddr *l3, time_t now)
{
int maclen;
unsigned char mac[DHCP_CHADDR_MAX];
if ((maclen = find_mac(l3, mac, 1, now)) != 0)
plen = add_pseudoheader(header, plen, limit, PACKETSZ, EDNS0_OPTION_MAC, mac, maclen, 0, 0);
return plen;
}
struct subnet_opt {
u16 family;
u8 source_netmask, scope_netmask;
#ifdef HAVE_IPV6
u8 addr[IN6ADDRSZ];
#else
u8 addr[INADDRSZ];
#endif
};
static void *get_addrp(union mysockaddr *addr, const short family)
{
#ifdef HAVE_IPV6
if (family == AF_INET6)
return &addr->in6.sin6_addr;
#endif
return &addr->in.sin_addr;
}
static size_t calc_subnet_opt(struct subnet_opt *opt, union mysockaddr *source)
{
/* http://tools.ietf.org/html/draft-vandergaast-edns-client-subnet-02 */
int len;
void *addrp = NULL;
int sa_family = source->sa.sa_family;
opt->source_netmask = 0;
opt->scope_netmask = 0;
#ifdef HAVE_IPV6
if (source->sa.sa_family == AF_INET6 && daemon->add_subnet6)
{
opt->source_netmask = daemon->add_subnet6->mask;
if (daemon->add_subnet6->addr_used)
{
sa_family = daemon->add_subnet6->addr.sa.sa_family;
addrp = get_addrp(&daemon->add_subnet6->addr, sa_family);
}
else
addrp = &source->in6.sin6_addr;
}
#endif
if (source->sa.sa_family == AF_INET && daemon->add_subnet4)
{
opt->source_netmask = daemon->add_subnet4->mask;
if (daemon->add_subnet4->addr_used)
{
sa_family = daemon->add_subnet4->addr.sa.sa_family;
addrp = get_addrp(&daemon->add_subnet4->addr, sa_family);
}
else
addrp = &source->in.sin_addr;
}
#ifdef HAVE_IPV6
opt->family = htons(sa_family == AF_INET6 ? 2 : 1);
#else
opt->family = htons(1);
#endif
len = 0;
if (addrp && opt->source_netmask != 0)
{
len = ((opt->source_netmask - 1) >> 3) + 1;
memcpy(opt->addr, addrp, len);
if (opt->source_netmask & 7)
opt->addr[len-1] &= 0xff << (8 - (opt->source_netmask & 7));
}
return len + 4;
}
static size_t add_source_addr(struct dns_header *header, size_t plen, unsigned char *limit, union mysockaddr *source)
{
/* http://tools.ietf.org/html/draft-vandergaast-edns-client-subnet-02 */
int len;
struct subnet_opt opt;
len = calc_subnet_opt(&opt, source);
return add_pseudoheader(header, plen, (unsigned char *)limit, PACKETSZ, EDNS0_OPTION_CLIENT_SUBNET, (unsigned char *)&opt, len, 0, 0);
}
int check_source(struct dns_header *header, size_t plen, unsigned char *pseudoheader, union mysockaddr *peer)
{
/* Section 9.2, Check that subnet option in reply matches. */
int len, calc_len;
struct subnet_opt opt;
unsigned char *p;
int code, i, rdlen;
calc_len = calc_subnet_opt(&opt, peer);
if (!(p = skip_name(pseudoheader, header, plen, 10)))
return 1;
p += 8; /* skip UDP length and RCODE */
GETSHORT(rdlen, p);
if (!CHECK_LEN(header, p, plen, rdlen))
return 1; /* bad packet */
/* check if option there */
for (i = 0; i + 4 < rdlen; i += len + 4)
{
GETSHORT(code, p);
GETSHORT(len, p);
if (code == EDNS0_OPTION_CLIENT_SUBNET)
{
/* make sure this doesn't mismatch. */
opt.scope_netmask = p[3];
if (len != calc_len || memcmp(p, &opt, len) != 0)
return 0;
}
p += len;
}
return 1;
}
size_t add_edns0_config(struct dns_header *header, size_t plen, unsigned char *limit,
union mysockaddr *source, time_t now, int *check_subnet)
{
*check_subnet = 0;
if (option_bool(OPT_ADD_MAC))
plen = add_mac(header, plen, limit, source, now);
if (option_bool(OPT_MAC_B64) || option_bool(OPT_MAC_HEX))
plen = add_dns_client(header, plen, limit, source, now);
if (daemon->dns_client_id)
plen = add_pseudoheader(header, plen, limit, PACKETSZ, EDNS0_OPTION_NOMCPEID,
(unsigned char *)daemon->dns_client_id, strlen(daemon->dns_client_id), 0, 1);
if (option_bool(OPT_CLIENT_SUBNET))
{
plen = add_source_addr(header, plen, limit, source);
*check_subnet = 1;
}
return plen;
}