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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
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97
dhcp.c
View file

@ -45,7 +45,6 @@ struct opt {
static struct opt opts[255] = {
[1] = { 0, 4, { 0 }, 0, { 0 }, }, /* Mask */
[3] = { 0, 4, { 0 }, 0, { 0 }, }, /* Router */
[6] = { 0, 4, { 0 }, 0, { 0 }, }, /* DNS */
[51] = { 0, 4, { 0xff, 0xff, 0xff, 0xff }, 0, { 0 }, }, /* Lease time */
[53] = { 0, 1, { 0 }, 0, { 0 }, }, /* Type */
#define DHCPDISCOVER 1
@ -154,6 +153,92 @@ static int fill(struct msg *m)
return offset;
}
/**
* opt_dns_search_dup_ptr() - Look for possible domain name compression pointer
* @buf: Current option buffer with existing labels
* @cmp: Portion of domain name being added
* @len: Length of current option buffer
*
* Return: offset to corresponding compression pointer if any, -1 if not found
*/
static int opt_dns_search_dup_ptr(unsigned char *buf, char *cmp, size_t len)
{
unsigned int i;
for (i = 0; i < len; i++) {
if (buf[i] == 0 &&
len - i - 1 >= strlen(cmp) &&
!memcmp(buf + i + 1, cmp, strlen(cmp)))
return i;
if ((buf[i] & 0xc0) == 0xc0 &&
len - i - 2 >= strlen(cmp) &&
!memcmp(buf + i + 2, cmp, strlen(cmp)))
return i + 1;
}
return -1;
}
/**
* opt_set_dns_search() - Fill data and set length for Domain Search option
* @c: Execution context
* @max_len: Maximum total length of option buffer
*/
static void opt_set_dns_search(struct ctx *c, size_t max_len)
{
char buf[NS_MAXDNAME];
int i;
opts[119].slen = 0;
for (i = 0; i < 255; i++)
max_len -= opts[i].slen;
for (i = 0; *c->dns_search[i].n; i++) {
unsigned int n;
int dup = -1;
char *p;
buf[0] = 0;
for (p = c->dns_search[i].n, n = 1; *p; p++) {
if (*p == '.') {
/* RFC 1035 4.1.4 Message compression */
dup = opt_dns_search_dup_ptr(opts[119].s, p + 1,
opts[119].slen);
if (dup >= 0) {
buf[n++] = '\xc0';
buf[n++] = dup;
break;
} else {
buf[n++] = '.';
}
} else {
buf[n++] = *p;
}
}
/* The compression pointer is also an end of label */
if (dup < 0)
buf[n++] = 0;
if (n >= max_len)
break;
memcpy(opts[119].s + opts[119].slen, buf, n);
opts[119].slen += n;
max_len -= n;
}
for (i = 0; i < opts[119].slen; i++) {
if (!opts[119].s[i] || opts[119].s[i] == '.') {
opts[119].s[i] = strcspn((char *)opts[119].s + i + 1,
".\xc0");
}
}
}
/**
* dhcp() - Check if this is a DHCP message, reply as needed
* @c: Execution context
@ -213,10 +298,16 @@ int dhcp(struct ctx *c, struct ethhdr *eh, size_t len)
m->yiaddr = c->addr4;
*(unsigned long *)opts[1].s = c->mask4;
*(unsigned long *)opts[3].s = c->gw4;
*(unsigned long *)opts[6].s = c->dns4;
*(unsigned long *)opts[54].s = c->gw4;
uh->len = htons(len = offsetof(struct msg, o) + fill(m));
for (i = 0, opts[6].slen = 0; c->dns4[i]; i++) {
((uint32_t *)opts[6].s)[i] = c->dns4[i];
opts[6].slen += sizeof(uint32_t);
}
opt_set_dns_search(c, sizeof(m->o));
uh->len = htons(len = offsetof(struct msg, o) + fill(m) + sizeof(*uh));
uh->check = 0;
uh->source = htons(67);
uh->dest = htons(68);

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)

54
ndp.c
View file

@ -14,6 +14,7 @@
#include <stdint.h>
#include <unistd.h>
#include <string.h>
#include <arpa/inet.h>
#include <linux/if_ether.h>
#include <linux/ip.h>
#include <linux/ipv6.h>
@ -21,7 +22,6 @@
#include <linux/udp.h>
#include <net/if.h>
#include <net/if_arp.h>
#include <arpa/inet.h>
#include "passt.h"
#include "util.h"
@ -76,6 +76,9 @@ int ndp(struct ctx *c, struct ethhdr *eh, size_t len)
memcpy(p, c->mac, ETH_ALEN);
p += 6;
} else if (ih->icmp6_type == RS) {
size_t len = 0;
int i, n;
info("NDP: received RS, sending RA");
ihr->icmp6_type = RA;
ihr->icmp6_code = 0;
@ -95,13 +98,48 @@ int ndp(struct ctx *c, struct ethhdr *eh, size_t len)
memcpy(p, &c->addr6, 8); /* prefix */
p += 16;
*p++ = 25; /* RDNS */
*p++ = 3; /* length */
p += 2;
*(uint32_t *)p = htonl(60); /* lifetime */
p += 4;
memcpy(p, &c->dns6, 16); /* address */
p += 16;
for (n = 0; !IN6_IS_ADDR_UNSPECIFIED(&c->dns6[n]); n++);
if (n) {
*p++ = 25; /* RDNSS */
*p++ = 1 + 2 * n; /* length */
p += 2; /* reserved */
*(uint32_t *)p = htonl(60); /* lifetime */
p += 4;
for (i = 0; i < n; i++) {
memcpy(p, &c->dns6[i], 16); /* address */
p += 16;
}
}
for (n = 0; *c->dns_search[n].n; n++)
len += strlen(c->dns_search[n].n) + 2;
if (len) {
*p++ = 31; /* DNSSL */
*p++ = 2 + (len + 8 - 1) / 8; /* length */
p += 2; /* reserved */
*(uint32_t *)p = htonl(60); /* lifetime */
p += 4;
for (i = 0; i < n; i++) {
char *dot;
*(p++) = '.';
strncpy((char *)p, c->dns_search[i].n,
sizeof(buf) -
((intptr_t)p - (intptr_t)buf));
for (dot = (char *)p - 1; *dot; dot++) {
if (*dot == '.')
*dot = strcspn(dot + 1, ".");
}
p += strlen(c->dns_search[i].n);
*(p++) = 0;
}
memset(p, 0, len % 8); /* padding */
p += len % 8;
}
*p++ = 1; /* source ll */
*p++ = 1; /* length */

77
passt.c
View file

@ -299,30 +299,49 @@ out:
*/
static void get_dns(struct ctx *c)
{
struct in6_addr *dns6 = &c->dns6[0];
struct fqdn *s = c->dns_search;
uint32_t *dns4 = &c->dns4[0];
char buf[BUFSIZ], *p, *end;
int dns4 = 0, dns6 = 0;
FILE *r;
r = fopen("/etc/resolv.conf", "r");
while (fgets(buf, BUFSIZ, r) && !(dns4 && dns6)) {
if (!strstr(buf, "nameserver "))
continue;
p = strrchr(buf, ' ');
end = strpbrk(buf, "%\n");
if (end)
*end = 0;
if (p && inet_pton(AF_INET, p + 1, &c->dns4))
dns4 = 1;
if (p && inet_pton(AF_INET6, p + 1, &c->dns6))
dns6 = 1;
while (fgets(buf, BUFSIZ, r)) {
if (strstr(buf, "nameserver ") == buf) {
p = strrchr(buf, ' ');
if (!p)
continue;
end = strpbrk(buf, "%\n");
if (end)
*end = 0;
if (dns4 - &c->dns4[0] < ARRAY_SIZE(c->dns4) &&
inet_pton(AF_INET, p + 1, dns4))
dns4++;
if (dns6 - &c->dns6[0] < ARRAY_SIZE(c->dns6) &&
inet_pton(AF_INET6, p + 1, dns6))
dns6++;
} else if (strstr(buf, "search ") == buf &&
s == c->dns_search) {
end = strpbrk(buf, "\n");
if (end)
*end = 0;
p = strtok(buf, " \t");
while ((p = strtok(NULL, " \t")) &&
s - c->dns_search < ARRAY_SIZE(c->dns_search)) {
strncpy(s->n, p, sizeof(c->dns_search[0]));
s++;
}
}
}
fclose(r);
if (dns4 || dns6)
return;
err("Couldn't get any nameserver address");
exit(EXIT_FAILURE);
if (dns4 == c->dns4 && dns6 == c->dns6)
warn("Couldn't get any nameserver address");
}
/**
@ -785,8 +804,17 @@ int main(int argc, char **argv)
inet_ntop(AF_INET, &c.mask4, buf4, sizeof(buf4)));
info(" router: %s",
inet_ntop(AF_INET, &c.gw4, buf4, sizeof(buf4)));
info(" DNS: %s",
inet_ntop(AF_INET, &c.dns4, buf4, sizeof(buf4)));
for (i = 0; c.dns4[i]; i++) {
if (!i)
info(" DNS:");
inet_ntop(AF_INET, &c.dns4[i], buf4, sizeof(buf4));
info(" %s", buf4);
}
for (i = 0; *c.dns_search[i].n; i++) {
if (!i)
info(" search:");
info(" %s", c.dns_search[i].n);
}
}
if (c.v6) {
info("NDP/DHCPv6:");
@ -794,8 +822,17 @@ int main(int argc, char **argv)
inet_ntop(AF_INET6, &c.addr6, buf6, sizeof(buf6)));
info(" router: %s",
inet_ntop(AF_INET6, &c.gw6, buf6, sizeof(buf6)));
info(" DNS: %s",
inet_ntop(AF_INET6, &c.dns6, buf6, sizeof(buf6)));
for (i = 0; !IN6_IS_ADDR_UNSPECIFIED(&c.dns6[i]); i++) {
if (!i)
info(" DNS:");
inet_ntop(AF_INET6, &c.dns6[i], buf6, sizeof(buf6));
info(" %s", buf6);
}
for (i = 0; *c.dns_search[i].n; i++) {
if (!i)
info(" search:");
info(" %s", c.dns_search[i].n);
}
}
listen:

17
passt.h
View file

@ -20,6 +20,12 @@ struct tap_msg {
#include "tcp.h"
#include "udp.h"
#include <resolv.h> /* For MAXNS below */
struct fqdn {
char n[NS_MAXDNAME];
};
/**
* struct ctx - Execution context
* @epollfd: file descriptor for epoll instance
@ -31,13 +37,14 @@ struct tap_msg {
* @addr4_seen: Latest IPv4 address seen as source from tap
* @mask4: IPv4 netmask, network order
* @gw4: Default IPv4 gateway, network order
* @dns4: IPv4 DNS address, network order
* @dns4: IPv4 DNS addresses, zero-terminated, network order
* @dns_search: DNS search list
* @v6: Enable IPv6 transport
* @addr6: IPv6 address for external, routable interface
* @addr6_seen: Latest IPv6 global/site address seen as source from tap
* @addr6_ll_seen: Latest IPv6 link-local address seen as source from tap
* @gw6: Default IPv6 gateway
* @dns4: IPv6 DNS address
* @dns4: IPv4 DNS addresses, zero-terminated
* @ifn: Name of routable interface
*/
struct ctx {
@ -51,14 +58,16 @@ struct ctx {
uint32_t addr4_seen;
uint32_t mask4;
uint32_t gw4;
uint32_t dns4;
uint32_t dns4[MAXNS + 1];
struct fqdn dns_search[MAXDNSRCH];
int v6;
struct in6_addr addr6;
struct in6_addr addr6_seen;
struct in6_addr addr6_ll_seen;
struct in6_addr gw6;
struct in6_addr dns6;
struct in6_addr dns6[MAXNS + 1];
char ifn[IF_NAMESIZE];

7
util.h
View file

@ -22,11 +22,16 @@ void debug(const char *format, ...);
CHECK_SET_MIN_MAX(c->proto_ctx.fd_, (fd)); \
} while (0)
#ifndef MIN
#define MIN(x, y) (((x) < (y)) ? (x) : (y))
#endif
#ifndef MAX
#define MAX(x, y) (((x) > (y)) ? (x) : (y))
#endif
#define ARRAY_SIZE(a) ((int)(sizeof(a) / sizeof((a)[0])))
#define IN_INTERVAL(a, b, x) ((x) >= (a) && (x) <= (b))
#define FD_PROTO(x, proto) \
(IN_INTERVAL(c->proto.fd_min, c->proto.fd_max, (x)))