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dhcp, ndp, dhcpv6: Support for multiple DNS servers, search list

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Add support for a variable amount of DNS servers, including zero,
from /etc/resolv.conf, in DHCP, NDP and DHCPv6 implementations.

Introduce support for domain search list for DHCP (RFC 3397),
NDP (RFC 8106), and DHCPv6 (RFC 3646), also sourced from
/etc/resolv.conf.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
This commit is contained in:
Stefano Brivio 2021-05-21 11:14:47 +02:00
parent 0231ac1c86
commit 9010054ea4
6 changed files with 312 additions and 45 deletions

105
dhcpv6.c
View file

@ -15,13 +15,13 @@
#include <unistd.h>
#include <string.h>
#include <time.h>
#include <arpa/inet.h>
#include <linux/if_ether.h>
#include <linux/ip.h>
#include <linux/ipv6.h>
#include <linux/udp.h>
#include <net/if.h>
#include <net/if_arp.h>
#include <arpa/inet.h>
#include "passt.h"
#include "tap.h"
@ -43,6 +43,7 @@ struct opt_hdr {
# define OPT_STATUS_CODE 13
# define STATUS_NOTONLINK 4
# define OPT_DNS_SERVERS 23
# define OPT_DNS_SEARCH 24
#else
# define OPT_CLIENTID __bswap_constant_16(1)
# define OPT_SERVERID __bswap_constant_16(2)
@ -52,6 +53,7 @@ struct opt_hdr {
# define OPT_STATUS_CODE __bswap_constant_16(13)
# define STATUS_NOTONLINK __bswap_constant_16(4)
# define OPT_DNS_SERVERS __bswap_constant_16(23)
# define OPT_DNS_SEARCH __bswap_constant_16(24)
#endif
#define STR_NOTONLINK "Prefix not appropriate for link."
@ -157,11 +159,21 @@ struct opt_status_code {
/**
* struct opt_dns_servers - DNS Recursive Name Server option (RFC 3646)
* @hdr: Option header
* @addr: IPv6 DNS address
* @addr: IPv6 DNS addresses
*/
struct opt_dns_servers {
struct opt_hdr hdr;
struct in6_addr addr;
struct in6_addr addr[MAXNS];
};
/**
* struct opt_dns_servers - Domain Search List option (RFC 3646)
* @hdr: Option header
* @list: NULL-separated list of domain names
*/
struct opt_dns_search {
struct opt_hdr hdr;
char list[MAXDNSRCH * NS_MAXDNAME];
};
/**
@ -200,8 +212,9 @@ static const struct udphdr uh_resp = {
* @server_id: Server Identifier option
* @ia_na: Non-temporary Address option
* @ia_addr: Address for IA_NA
* @dns_servers: DNS Recursive Name Server option
* @client_id: Client Identifier, variable length, must be at the end
* @client_id: Client Identifier, variable length
* @dns_servers: DNS Recursive Name Server, here just for storage size
* @dns_search: Domain Search List, here just for storage size
*/
static struct resp_t {
struct udphdr uh;
@ -211,6 +224,8 @@ static struct resp_t {
struct opt_ia_na ia_na;
struct opt_ia_addr ia_addr;
struct opt_client_id client_id;
struct opt_dns_servers dns_servers;
struct opt_dns_search dns_search;
} __attribute__((__packed__)) resp = {
uh_resp,
{ 0 },
@ -226,10 +241,17 @@ static struct resp_t {
IN6ADDR_ANY_INIT, (uint32_t)~0U, (uint32_t)~0U
},
{ { OPT_CLIENTID, 0, },
{ 0 }
},
{ { OPT_DNS_SERVERS, 0, },
{ IN6ADDR_ANY_INIT }
},
{ { OPT_DNS_SEARCH, 0, },
{ 0 },
},
};
static const struct opt_status_code sc_not_on_link = {
@ -352,6 +374,67 @@ ia_ta:
return NULL;
}
/**
* dhcpv6_dns_fill() - Fill in DNS Servers and Domain Search list options
* @c: Execution context
* @buf: Response message buffer where options will be appended
* @offset: Offset in message buffer for new options
*
* Return: updated length of response message buffer.
*/
static size_t dhcpv6_dns_fill(struct ctx *c, char *buf, int offset)
{
struct opt_dns_servers *srv = NULL;
struct opt_dns_search *srch = NULL;
int i;
for (i = 0; !IN6_IS_ADDR_UNSPECIFIED(&c->dns6[i]); i++) {
if (!i) {
srv = (struct opt_dns_servers *)(buf + offset);
offset += sizeof(struct opt_hdr);
srv->hdr.t = OPT_DNS_SERVERS;
srv->hdr.l = 0;
}
memcpy(&srv->addr[i], &c->dns6[i], sizeof(srv->addr[i]));
srv->hdr.l += sizeof(srv->addr[i]);
offset += sizeof(srv->addr[i]);
}
if (srv)
srv->hdr.l = htons(srv->hdr.l);
for (i = 0; *c->dns_search[i].n; i++) {
char *p;
if (!i) {
srch = (struct opt_dns_search *)(buf + offset);
offset += sizeof(struct opt_hdr);
srch->hdr.t = OPT_DNS_SEARCH;
srch->hdr.l = 0;
p = srch->list;
*p = 0;
}
p = stpcpy(p + 1, c->dns_search[i].n);
*(p++) = 0;
srch->hdr.l += strlen(c->dns_search[i].n) + 2;
offset += strlen(c->dns_search[i].n) + 2;
}
if (srch) {
for (i = 0; i < srch->hdr.l; i++) {
if (srch->list[i] == '.' || !srch->list[i]) {
srch->list[i] = strcspn(srch->list + i + 1,
".");
}
}
srch->hdr.l = htons(srch->hdr.l);
}
return offset;
}
/**
* dhcpv6() - Check if this is a DHCPv6 message, reply as needed
* @c: Execution context
@ -478,10 +561,14 @@ int dhcpv6(struct ctx *c, struct ethhdr *eh, size_t len)
memcpy(&resp.client_id, client_id,
ntohs(client_id->l) + sizeof(struct opt_hdr));
resp.uh.len = htons(n = offsetof(struct resp_t, client_id) +
sizeof(struct opt_hdr) + ntohs(client_id->l));
n = offsetof(struct resp_t, client_id) +
sizeof(struct opt_hdr) + ntohs(client_id->l);
n = dhcpv6_dns_fill(c, (char *)&resp, n);
resp.uh.len = htons(n);
resp.hdr.xid = mh->xid;
tap_ip_send(c, &c->gw6, IPPROTO_UDP, (char *)&resp, n);
c->addr6_seen = c->addr6;
@ -489,7 +576,7 @@ int dhcpv6(struct ctx *c, struct ethhdr *eh, size_t len)
}
/**
* dhcpv6() - Initialise DUID and addresses for DHCPv6 server
* dhcpv6_init() - Initialise DUID and addresses for DHCPv6 server
* @c: Execution context
*/
void dhcpv6_init(struct ctx *c)