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

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>

6 files changed, 312 insertions, 45 deletions

diff --git a/dhcp.c b/dhcp.c
index cff9403..6448e51 100644
--- a/dhcp.c
+++ b/dhcp.c
@@ -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
@@ -155,6 +154,92 @@ static int fill(struct msg *m)
 }
 
 /**
+ * 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
  * @len:	Total L2 packet length
@@ -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);
diff --git a/dhcpv6.c b/dhcpv6.c
index 6e006dd..4ce7a87 100644
--- a/dhcpv6.c
+++ b/dhcpv6.c
@@ -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 = {
@@ -353,6 +375,67 @@ ia_ta:
 }
 
 /**
+ * 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
  * @eh:		Packet buffer, Ethernet header
@@ -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)
diff --git a/ndp.c b/ndp.c
index 1e0d817..40cfe93 100644
--- a/ndp.c
+++ b/ndp.c
@@ -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 */
diff --git a/passt.c b/passt.c
index c2c630e..d0dcb26 100644
--- a/passt.c
+++ b/passt.c
@@ -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:
diff --git a/passt.h b/passt.h
index 22a91d6..bfbdc06 100644
--- a/passt.h
+++ b/passt.h
@@ -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];
 
diff --git a/util.h b/util.h
index fe129ee..7d0704c 100644
--- a/util.h
+++ b/util.h
@@ -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 IN_INTERVAL(a, b, x)	((x) >= (a) && (x) <= (b))
+#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)))