[PATCH v5] dhcp, dhcpv6: Add hostname and client fqdn ops

[Enrique Llorente <ellorent@redhat.com>]

Both DHCPv4 and DHCPv6 has the capability to pass the hostname to
clients, the DHCPv4 uses option 12 (hostname) while the DHCPv6 uses option 39
(client fqdn), for some virt deployments like kubevirt is expected to
have the VirtualMachine name as the guest hostname.

This change add the following arguments:
 - -H --hostname NAME to configure the hostname DHCPv4 option(12)
 - --fqdn NAME to configure client fqdn option for both DHCPv4(81) and
   DHCPv6(39)

Signed-off-by: Enrique Llorente <ellorent@redhat.com>
---
 conf.c           | 20 +++++++++++--
 dhcp.c           | 50 ++++++++++++++++++++++++++++----
 dhcpv6.c         | 75 +++++++++++++++++++++++++++++++++++++++---------
 passt.1          | 11 +++++++
 passt.h          |  5 ++++
 pasta.c          | 18 ++++++++----
 test/lib/setup   | 10 +++----
 test/passt.mbuto |  6 ++--
 test/passt/dhcp  | 15 +++++++++-
 util.c           | 23 +++++++++++++++
 util.h           |  6 ++++
 11 files changed, 204 insertions(+), 35 deletions(-)

diff --git a/conf.c b/conf.c
index df2b016..5f21193 100644
--- a/conf.c
+++ b/conf.c
@@ -854,7 +854,9 @@ static void usage(const char *name, FILE *f, int status)
 		FPRINTF(f, "    default: use addresses from /etc/resolv.conf\n");
 	FPRINTF(f,
 		"  -S, --search LIST	Space-separated list, search domains\n"
-		"    a single, empty option disables the DNS search list\n");
+		"    a single, empty option disables the DNS search list\n"
+		"  -H, --hostname NAME 	Hostname to configure client with\n"
+		"  --fqdn NAME		FQDN to configure client with\n");
 	if (strstr(name, "pasta"))
 		FPRINTF(f, "    default: don't use any search list\n");
 	else
@@ -1313,6 +1315,7 @@ void conf(struct ctx *c, int argc, char **argv)
 		{"outbound",	required_argument,	NULL,		'o' },
 		{"dns",		required_argument,	NULL,		'D' },
 		{"search",	required_argument,	NULL,		'S' },
+		{"hostname",	required_argument,	NULL,		'H' },
 		{"no-tcp",	no_argument,		&c->no_tcp,	1 },
 		{"no-udp",	no_argument,		&c->no_udp,	1 },
 		{"no-icmp",	no_argument,		&c->no_icmp,	1 },
@@ -1357,6 +1360,7 @@ void conf(struct ctx *c, int argc, char **argv)
 		/* vhost-user backend program convention */
 		{"print-capabilities", no_argument,	NULL,		26 },
 		{"socket-path",	required_argument,	NULL,		's' },
+		{"fqdn",	required_argument,	NULL,		27 },
 		{ 0 },
 	};
 	const char *logname = (c->mode == MODE_PASTA) ? "pasta" : "passt";
@@ -1379,9 +1383,9 @@ void conf(struct ctx *c, int argc, char **argv)
 	if (c->mode == MODE_PASTA) {
 		c->no_dhcp_dns = c->no_dhcp_dns_search = 1;
 		fwd_default = FWD_AUTO;
-		optstring = "+dqfel:hF:I:p:P:m:a:n:M:g:i:o:D:S:46t:u:T:U:";
+		optstring = "+dqfel:hF:I:p:P:m:a:n:M:g:i:o:D:S:H:46t:u:T:U:";
 	} else {
-		optstring = "+dqfel:hs:F:p:P:m:a:n:M:g:i:o:D:S:461t:u:";
+		optstring = "+dqfel:hs:F:p:P:m:a:n:M:g:i:o:D:S:H:461t:u:";
 	}
 
 	c->tcp.fwd_in.mode = c->tcp.fwd_out.mode = FWD_UNSET;
@@ -1558,6 +1562,11 @@ void conf(struct ctx *c, int argc, char **argv)
 		case 26:
 			vu_print_capabilities();
 			break;
+		case 27:
+			if (snprintf_check(c->fqdn, PASST_MAXDNAME,
+		            "%s", optarg))
+				die("Invalid FQDN: %s", optarg);
+			break;
 		case 'd':
 			c->debug = 1;
 			c->quiet = 0;
@@ -1727,6 +1736,11 @@ void conf(struct ctx *c, int argc, char **argv)
 
 			die("Cannot use DNS search domain %s", optarg);
 			break;
+		case 'H':
+			if (snprintf_check(c->hostname, PASST_MAXDNAME,
+			    "%s", optarg))
+				die("Invalid hostname: %s", optarg);
+			break;
 		case '4':
 			v4_only = true;
 			v6_only = false;
diff --git a/dhcp.c b/dhcp.c
index d8515aa..b224bf8 100644
--- a/dhcp.c
+++ b/dhcp.c
@@ -63,6 +63,12 @@ static struct opt opts[255];
 
 #define OPT_MIN		60 /* RFC 951 */
 
+/* 576 (RFC 2131), minus offset
+ * of options (268), minus end
+ * option and its length (2)
+ */
+#define OPT_MAX		306
+
 /**
  * dhcp_init() - Initialise DHCP options
  */
@@ -122,7 +128,7 @@ struct msg {
 	uint8_t sname[64];
 	uint8_t file[128];
 	uint32_t magic;
-	uint8_t o[308];
+	uint8_t o[OPT_MAX + 2]; /* End option and length */
 } __attribute__((__packed__));
 
 /**
@@ -130,15 +136,31 @@ struct msg {
  * @m:		Message to fill
  * @o:		Option number
  * @offset:	Current offset within options field, updated on insertion
+ *
+ * Return: offset for the next option field
  */
-static void fill_one(struct msg *m, int o, int *offset)
+static int fill_one(struct msg *m, int o, int *offset)
 {
+	size_t idx, slen = 0;
+
+	/* If it cannot write even enum + len + one byte, then just skip */
+	if (*offset + 2 > OPT_MAX)
+		return OPT_MAX;
+
 	m->o[*offset] = o;
 	m->o[*offset + 1] = opts[o].slen;
-	memcpy(&m->o[*offset + 2], opts[o].s, opts[o].slen);
+	idx = *offset + 2;
+	slen = opts[o].slen;
+
+	/* Truncate if it goes beyond OPT_MAX */
+	if (idx + slen > OPT_MAX)
+		slen = OPT_MAX - idx;
+	
+	memcpy(&m->o[*offset + 2], opts[o].s, slen);
 
 	opts[o].sent = 1;
 	*offset += 2 + opts[o].slen;
+	return *offset;
 }
 
 /**
@@ -172,7 +194,10 @@ static int fill(struct msg *m)
 
 	for (o = 0; o < 255; o++) {
 		if (opts[o].slen != -1 && !opts[o].sent)
-			fill_one(m, o, &offset);
+			if (fill_one(m, o, &offset) == OPT_MAX) {
+				debug("DHCP: truncating after option %i", o);
+				break;
+			}
 	}
 
 	m->o[offset++] = 255;
@@ -285,7 +310,7 @@ static void opt_set_dns_search(const struct ctx *c, size_t max_len)
  */
 int dhcp(const struct ctx *c, const struct pool *p)
 {
-	size_t mlen, dlen, offset = 0, opt_len, opt_off = 0;
+	size_t mlen, dlen, offset = 0, opt_len, opt_off = 0, hostname_len = 0, fqdn_len = 0;
 	char macstr[ETH_ADDRSTRLEN];
 	struct in_addr mask, dst;
 	const struct ethhdr *eh;
@@ -398,6 +423,21 @@ int dhcp(const struct ctx *c, const struct pool *p)
 	if (!opts[6].slen)
 		opts[6].slen = -1;
 
+	hostname_len = strlen(c->hostname);
+	if (hostname_len > 0) {
+		opts[12].slen = hostname_len;
+		memcpy(opts[12].s, &c->hostname, hostname_len);
+	}
+
+	fqdn_len = strlen(c->fqdn);
+	if (fqdn_len > 0) {
+		size_t encoded_len = 0;
+		opts[81].s[0] = 0x4; /* flags (E) */
+		encoded_len = encode_domain_name(c->fqdn, fqdn_len,
+							(char *) opts[81].s + 3);
+		opts[81].slen = encoded_len + 3;
+	}
+
 	if (!c->no_dhcp_dns_search)
 		opt_set_dns_search(c, sizeof(m->o));
 
diff --git a/dhcpv6.c b/dhcpv6.c
index 0523bba..ce3a1bd 100644
--- a/dhcpv6.c
+++ b/dhcpv6.c
@@ -48,6 +48,7 @@ struct opt_hdr {
 # define  STATUS_NOTONLINK	htons_constant(4)
 # define OPT_DNS_SERVERS	htons_constant(23)
 # define OPT_DNS_SEARCH		htons_constant(24)
+# define OPT_CLIENT_FQDN	htons_constant(39)
 #define   STR_NOTONLINK		"Prefix not appropriate for link."
 
 	uint16_t l;
@@ -58,6 +59,9 @@ struct opt_hdr {
 					      sizeof(struct opt_hdr))
 #define OPT_VSIZE(x)		(sizeof(struct opt_##x) - 		\
 				 sizeof(struct opt_hdr))
+#define OPT_MAX_SIZE		IPV6_MIN_MTU - (sizeof(struct ipv6hdr) + \
+					        sizeof(struct udphdr) + \
+					        sizeof(struct msg_hdr))
 
 /**
  * struct opt_client_id - DHCPv6 Client Identifier option
@@ -163,6 +167,18 @@ struct opt_dns_search {
 	char list[MAXDNSRCH * NS_MAXDNAME];
 } __attribute__((packed));
 
+/**
+ * struct opt_client_fqdn - Client FQDN option (RFC 4704)
+ * @hdr:		Option header
+ * @flags:		Flags described by RFC 4704 (always zero for us)
+ * @domain_name:	Client FQDN
+ */
+struct opt_client_fqdn{
+	struct opt_hdr hdr;
+	uint8_t flags;
+	char domain_name[PASST_MAXDNAME];
+} __attribute__((packed));
+
 /**
  * struct msg_hdr - DHCPv6 client/server message header
  * @type:		DHCP message type
@@ -193,6 +209,7 @@ struct msg_hdr {
  * @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
+ * @client_fqdn:	Client FQDN, variable length
  */
 static struct resp_t {
 	struct msg_hdr hdr;
@@ -203,6 +220,7 @@ static struct resp_t {
 	struct opt_client_id client_id;
 	struct opt_dns_servers dns_servers;
 	struct opt_dns_search dns_search;
+	struct opt_client_fqdn client_fqdn;
 } __attribute__((__packed__)) resp = {
 	{ 0 },
 	SERVER_ID,
@@ -228,6 +246,10 @@ static struct resp_t {
 	{ { OPT_DNS_SEARCH,	0, },
 	  { 0 },
 	},
+
+	{ { OPT_CLIENT_FQDN, 0, },
+	  0, { 0 },
+	},
 };
 
 static const struct opt_status_code sc_not_on_link = {
@@ -346,7 +368,6 @@ static size_t dhcpv6_dns_fill(const struct ctx *c, char *buf, int offset)
 {
 	struct opt_dns_servers *srv = NULL;
 	struct opt_dns_search *srch = NULL;
-	char *p = NULL;
 	int i;
 
 	if (c->no_dhcp_dns)
@@ -373,6 +394,7 @@ search:
 		return offset;
 
 	for (i = 0; *c->dns_search[i].n; i++) {
+		size_t encoded_name_len = 0;
 		size_t name_len = strlen(c->dns_search[i].n);
 
 		/* We already append separators, don't duplicate if present */
@@ -388,29 +410,53 @@ search:
 			offset += sizeof(struct opt_hdr);
 			srch->hdr.t = OPT_DNS_SEARCH;
 			srch->hdr.l = 0;
-			p = srch->list;
 		}
-
-		*p = '.';
-		p = stpncpy(p + 1, c->dns_search[i].n, name_len);
-		p++;
-		srch->hdr.l += name_len + 2;
-		offset += name_len + 2;
+		
+		encoded_name_len = encode_domain_name(c->dns_search[i].n, 
+				   name_len, srch->list);
+		srch->hdr.l += encoded_name_len;
+		offset += encoded_name_len;
 	}
 
 	if (srch) {
-		for (i = 0; i < srch->hdr.l; i++) {
-			if (srch->list[i] == '.') {
-				srch->list[i] = strcspn(srch->list + i + 1,
-							".");
-			}
-		}
 		srch->hdr.l = htons(srch->hdr.l);
 	}
 
 	return offset;
 }
 
+/**
+ * dhcpv6_client_fqdn_fill() - Fill in client FQDN option
+ * @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_client_fqdn_fill(const struct ctx *c, char *buf, int offset)
+{
+	size_t fqdn_len, opt_hdr_len, opt_len, encoded_fqdn_len;
+	struct opt_client_fqdn *o;
+	
+	opt_hdr_len = sizeof(struct opt_hdr);
+
+	fqdn_len = MIN(strlen(c->fqdn), OPT_MAX_SIZE - (offset + opt_hdr_len + 1));
+	
+	if (fqdn_len == 0)
+		return offset;
+
+	o = (struct opt_client_fqdn *)(buf + offset);
+	encoded_fqdn_len = encode_domain_name(c->fqdn, fqdn_len, 
+							o->domain_name);
+	opt_len = encoded_fqdn_len + 1;
+
+	o->hdr.t = OPT_CLIENT_FQDN;
+	o->hdr.l = htons(opt_len);
+	o->flags = 0x00;
+
+	return offset + opt_hdr_len + opt_len;
+}
+
 /**
  * dhcpv6() - Check if this is a DHCPv6 message, reply as needed
  * @c:		Execution context
@@ -544,6 +590,7 @@ int dhcpv6(struct ctx *c, const struct pool *p,
 	n = offsetof(struct resp_t, client_id) +
 	    sizeof(struct opt_hdr) + ntohs(client_id->l);
 	n = dhcpv6_dns_fill(c, (char *)&resp, n);
+	n = dhcpv6_client_fqdn_fill(c, (char *)&resp, n);
 
 	resp.hdr.xid = mh->xid;
 
diff --git a/passt.1 b/passt.1
index d9cd33e..8f6b194 100644
--- a/passt.1
+++ b/passt.1
@@ -401,6 +401,17 @@ Enable IPv6-only operation. IPv4 traffic will be ignored.
 By default, IPv4 operation is enabled as long as at least an IPv4 route and an
 interface address are configured on a given host interface.
 
+.TP
+.BR \-H ", " \-\-hostname " " \fIname
+Hostname to configure client with.
+Send \fIname as DHCP option 12 (hostname).
+
+.TP
+.BR \-\-fqdn " " \fIname
+FQDN to configure client with.
+Send \fIname as dhcp client fqdn option, for DHCP option 81 and for
+DHCPv6 option 39.
+
 .SS \fBpasst\fR-only options
 
 .TP
diff --git a/passt.h b/passt.h
index 0dd4efa..9909a10 100644
--- a/passt.h
+++ b/passt.h
@@ -209,6 +209,8 @@ struct ip6_ctx {
  * @ifi4:		Template interface for IPv4, -1: none, 0: IPv4 disabled
  * @ip:			IPv4 configuration
  * @dns_search:		DNS search list
+ * @hostname:		Guest hostname
+ * @fqdn:		Guest FQDN
  * @ifi6:		Template interface for IPv6, -1: none, 0: IPv6 disabled
  * @ip6:		IPv6 configuration
  * @pasta_ifn:		Name of namespace interface for pasta
@@ -268,6 +270,9 @@ struct ctx {
 	struct ip4_ctx ip4;
 
 	struct fqdn dns_search[MAXDNSRCH];
+	
+    char hostname[PASST_MAXDNAME];
+    char fqdn[PASST_MAXDNAME];
 
 	int ifi6;
 	struct ip6_ctx ip6;
diff --git a/pasta.c b/pasta.c
index ff41c95..00678f3 100644
--- a/pasta.c
+++ b/pasta.c
@@ -173,6 +173,7 @@ void pasta_open_ns(struct ctx *c, const char *netns)
 struct pasta_spawn_cmd_arg {
 	const char *exe;
 	char *const *argv;
+	struct ctx *c;
 };
 
 /**
@@ -186,6 +187,7 @@ static int pasta_spawn_cmd(void *arg)
 {
 	char hostname[HOST_NAME_MAX + 1] = HOSTNAME_PREFIX;
 	const struct pasta_spawn_cmd_arg *a;
+	size_t conf_hostname_len;
 	sigset_t set;
 
 	/* We run in a detached PID and mount namespace: mount /proc over */
@@ -194,10 +196,16 @@ static int pasta_spawn_cmd(void *arg)
 
 	if (write_file("/proc/sys/net/ipv4/ping_group_range", "0 0"))
 		warn("Cannot set ping_group_range, ICMP requests might fail");
-
-	if (!gethostname(hostname + sizeof(HOSTNAME_PREFIX) - 1,
-			 HOST_NAME_MAX + 1 - sizeof(HOSTNAME_PREFIX)) ||
-	    errno == ENAMETOOLONG) {
+	
+	a = (const struct pasta_spawn_cmd_arg *)arg;
+	
+	conf_hostname_len = strlen(a->c->hostname);
+	if (conf_hostname_len > 0) {
+		if (sethostname(a->c->hostname, conf_hostname_len))
+			warn("Unable to set configured hostname");
+	}else if (!gethostname(hostname + sizeof(HOSTNAME_PREFIX) - 1,
+		   HOST_NAME_MAX + 1 - sizeof(HOSTNAME_PREFIX)) ||
+	      errno == ENAMETOOLONG) {
 		hostname[HOST_NAME_MAX] = '\0';
 		if (sethostname(hostname, strlen(hostname)))
 			warn("Unable to set pasta-prefixed hostname");
@@ -208,7 +216,6 @@ static int pasta_spawn_cmd(void *arg)
 	sigaddset(&set, SIGUSR1);
 	sigwaitinfo(&set, NULL);
 
-	a = (const struct pasta_spawn_cmd_arg *)arg;
 	execvp(a->exe, a->argv);
 
 	die_perror("Failed to start command or shell");
@@ -230,6 +237,7 @@ void pasta_start_ns(struct ctx *c, uid_t uid, gid_t gid,
 	struct pasta_spawn_cmd_arg arg = {
 		.exe = argv[0],
 		.argv = argv,
+		.c = c,
 	};
 	char uidmap[BUFSIZ], gidmap[BUFSIZ];
 	char *sh_argv[] = { NULL, NULL };
diff --git a/test/lib/setup b/test/lib/setup
index 580825f..ee67152 100755
--- a/test/lib/setup
+++ b/test/lib/setup
@@ -49,7 +49,7 @@ setup_passt() {
 
 	context_run passt "make clean"
 	context_run passt "make valgrind"
-	context_run_bg passt "valgrind --max-stackframe=$((4 * 1024 * 1024)) --trace-children=yes --vgdb=no --error-exitcode=1 --suppressions=test/valgrind.supp ./passt ${__opts} -s ${STATESETUP}/passt.socket -f -t 10001 -u 10001 -P ${STATESETUP}/passt.pid"
+	context_run_bg passt "valgrind --max-stackframe=$((4 * 1024 * 1024)) --trace-children=yes --vgdb=no --error-exitcode=1 --suppressions=test/valgrind.supp ./passt ${__opts} -s ${STATESETUP}/passt.socket -f -t 10001 -u 10001 -H hostname1 --fqdn fqdn1.passt.test -P ${STATESETUP}/passt.pid"
 
 	# pidfile isn't created until passt is listening
 	wait_for [ -f "${STATESETUP}/passt.pid" ]
@@ -160,11 +160,11 @@ setup_passt_in_ns() {
 	if [ ${VALGRIND} -eq 1 ]; then
 		context_run passt "make clean"
 		context_run passt "make valgrind"
-		context_run_bg passt "valgrind --max-stackframe=$((4 * 1024 * 1024)) --trace-children=yes --vgdb=no --error-exitcode=1 --suppressions=test/valgrind.supp ./passt -f ${__opts} -s ${STATESETUP}/passt.socket -t 10001,10011,10021,10031 -u 10001,10011,10021,10031 -P ${STATESETUP}/passt.pid --map-host-loopback ${__map_ns4} --map-host-loopback ${__map_ns6}"
+		context_run_bg passt "valgrind --max-stackframe=$((4 * 1024 * 1024)) --trace-children=yes --vgdb=no --error-exitcode=1 --suppressions=test/valgrind.supp ./passt -f ${__opts} -s ${STATESETUP}/passt.socket -H hostname1 --fqdn fqdn1.passt.test -t 10001,10011,10021,10031 -u 10001,10011,10021,10031 -P ${STATESETUP}/passt.pid --map-host-loopback ${__map_ns4} --map-host-loopback ${__map_ns6}"
 	else
 		context_run passt "make clean"
 		context_run passt "make"
-		context_run_bg passt "./passt -f ${__opts} -s ${STATESETUP}/passt.socket -t 10001,10011,10021,10031 -u 10001,10011,10021,10031 -P ${STATESETUP}/passt.pid --map-host-loopback ${__map_ns4} --map-host-loopback ${__map_ns6}"
+		context_run_bg passt "./passt -f ${__opts} -s ${STATESETUP}/passt.socket -H hostname1 --fqdn fqdn1.passt.test -t 10001,10011,10021,10031 -u 10001,10011,10021,10031 -P ${STATESETUP}/passt.pid --map-host-loopback ${__map_ns4} --map-host-loopback ${__map_ns6}"
 	fi
 	wait_for [ -f "${STATESETUP}/passt.pid" ]
 
@@ -243,7 +243,7 @@ setup_two_guests() {
 	[ ${TRACE} -eq 1 ] && __opts="${__opts} --trace"
 	[ ${VHOST_USER} -eq 1 ] && __opts="${__opts} --vhost-user"
 
-	context_run_bg passt_1 "./passt -s ${STATESETUP}/passt_1.socket -P ${STATESETUP}/passt_1.pid -f ${__opts} -t 10001 -u 10001"
+	context_run_bg passt_1 "./passt -s ${STATESETUP}/passt_1.socket -P ${STATESETUP}/passt_1.pid -f ${__opts} --fqdn fqdn1.passt.test -H hostname1 -t 10001 -u 10001"
 	wait_for [ -f "${STATESETUP}/passt_1.pid" ]
 
 	__opts=
@@ -252,7 +252,7 @@ setup_two_guests() {
 	[ ${TRACE} -eq 1 ] && __opts="${__opts} --trace"
 	[ ${VHOST_USER} -eq 1 ] && __opts="${__opts} --vhost-user"
 
-	context_run_bg passt_2 "./passt -s ${STATESETUP}/passt_2.socket -P ${STATESETUP}/passt_2.pid -f ${__opts} -t 10004 -u 10004"
+	context_run_bg passt_2 "./passt -s ${STATESETUP}/passt_2.socket -P ${STATESETUP}/passt_2.pid -f ${__opts} --hostname hostname2 --fqdn fqdn2 -t 10004 -u 10004"
 	wait_for [ -f "${STATESETUP}/passt_2.pid" ]
 
 	__vmem="$((${MEM_KIB} / 1024 / 4))"
diff --git a/test/passt.mbuto b/test/passt.mbuto
index 138d365..1e07693 100755
--- a/test/passt.mbuto
+++ b/test/passt.mbuto
@@ -13,7 +13,7 @@
 PROGS="${PROGS:-ash,dash,bash ip mount ls insmod mkdir ln cat chmod lsmod
        modprobe find grep mknod mv rm umount jq iperf3 dhclient hostname
        sed tr chown sipcalc cut socat dd strace ping tail killall sleep sysctl
-       nproc tcp_rr tcp_crr udp_rr which tee seq bc sshd ssh-keygen cmp}"
+       nproc tcp_rr tcp_crr udp_rr which tee seq bc sshd ssh-keygen cmp env}"
 
 # OpenSSH 9.8 introduced split binaries, with sshd being the daemon, and
 # sshd-session the per-session program. We need the latter as well, and the path
@@ -41,6 +41,7 @@ FIXUP="${FIXUP}"'
 #!/bin/sh
 LOG=/var/log/dhclient-script.log
 echo \${reason} \${interface} >> \$LOG
+env >> \$LOG
 set >> \$LOG
 
 [ -n "\${new_interface_mtu}" ]       && ip link set dev \${interface} mtu \${new_interface_mtu}
@@ -54,7 +55,8 @@ set >> \$LOG
 [ -n "\${new_ip6_address}" ]         && ip addr add \${new_ip6_address}/\${new_ip6_prefixlen} dev \${interface}
 [ -n "\${new_dhcp6_name_servers}" ]  && for d in \${new_dhcp6_name_servers}; do echo "nameserver \${d}%\${interface}" >> /etc/resolv.conf; done
 [ -n "\${new_dhcp6_domain_search}" ] && (printf "search"; for d in \${new_dhcp6_domain_search}; do printf " %s" "\${d}"; done; printf "\n") >> /etc/resolv.conf
-[ -n "\${new_host_name}" ]           && hostname "\${new_host_name}"
+[ -n "\${new_host_name}" ]           && echo "\${new_host_name}" > /tmp/new_host_name
+[ -n "\${new_fqdn_fqdn}" ]           && echo "\${new_fqdn_fqdn}" > /tmp/new_fqdn_fqdn
 exit 0
 EOF
 	chmod 755 /sbin/dhclient-script
diff --git a/test/passt/dhcp b/test/passt/dhcp
index 9925ab9..145f1ba 100644
--- a/test/passt/dhcp
+++ b/test/passt/dhcp
@@ -11,7 +11,7 @@
 # Copyright (c) 2021 Red Hat GmbH
 # Author: Stefano Brivio <sbrivio@redhat.com>
 
-gtools	ip jq dhclient sed tr
+gtools	ip jq dhclient sed tr hostname
 htools	ip jq sed tr head
 
 test	Interface name
@@ -47,7 +47,16 @@ gout	SEARCH sed 's/\. / /g' /etc/resolv.conf | sed 's/\.$//g' | sed -n 's/^searc
 hout	HOST_SEARCH sed 's/\. / /g' /etc/resolv.conf | sed 's/\.$//g' | sed -n 's/^search \(.*\)/\1/p' | tr ' \n' ',' | sed 's/,$//;s/$/\n/'
 check	[ "__SEARCH__" = "__HOST_SEARCH__" ]
 
+test	DHCP: Hostname
+gout	NEW_HOST_NAME cat /tmp/new_host_name
+check	[ "__NEW_HOST_NAME__" = "hostname1" ]
+
+test	DHCP: Client FQDN
+gout	NEW_FQDN_FQDN cat /tmp/new_fqdn_fqdn
+check	[ "__NEW_FQDN_FQDN__" = "fqdn1.passt.test" ]
+
 test	DHCPv6: address
+guest	rm /tmp/new_fqdn_fqdn
 guest	/sbin/dhclient -6 __IFNAME__
 # Wait for DAD to complete
 guest	while ip -j -6 addr show tentative | jq -e '.[].addr_info'; do sleep 0.1; done
@@ -70,3 +79,7 @@ test	DHCPv6: search list
 gout	SEARCH6 sed 's/\. / /g' /etc/resolv.conf | sed 's/\.$//g' | sed -n 's/^search \(.*\)/\1/p' | tr ' \n' ',' | sed 's/,$//;s/$/\n/'
 hout	HOST_SEARCH6 sed 's/\. / /g' /etc/resolv.conf | sed 's/\.$//g' | sed -n 's/^search \(.*\)/\1/p' | tr ' \n' ',' | sed 's/,$//;s/$/\n/'
 check	[ "__SEARCH6__" = "__HOST_SEARCH6__" ]
+
+test	DHCPv6: Hostname
+gout	NEW_FQDN_FQDN cat /tmp/new_fqdn_fqdn
+check	[ "__NEW_FQDN_FQDN__" = "fqdn1.passt.test" ]
diff --git a/util.c b/util.c
index 11973c4..7aeb5b4 100644
--- a/util.c
+++ b/util.c
@@ -837,3 +837,26 @@ void raw_random(void *buf, size_t buflen)
 	if (random_read < buflen)
 		die("Unexpected EOF on random data source");
 }
+/**
+ * encode_domain_name() - Encode domain name according to RFC 1035, section 3.1
+ * @domain_name:	Input domain name to encode
+ * @len:	Domain name length
+ * @buf:	Buffer to fill in with encoded domain name
+ *
+ * Return: encoded domain name length
+ */
+size_t encode_domain_name(const char *domain_name, size_t len, char *buf)
+{
+	char *p;
+	size_t i;
+
+	buf[0] = strcspn(domain_name, ".");
+	p = buf + 1;
+	for (i = 0; i < len; i++) {
+		if (domain_name[i] == '.') 
+			p[i] = strcspn(domain_name + i + 1, ".");
+		else 
+			p[i] = domain_name[i];
+	}
+	return len + 2;
+}
diff --git a/util.h b/util.h
index 3fa1d12..c55ef29 100644
--- a/util.h
+++ b/util.h
@@ -40,6 +40,9 @@
 #ifndef IP_MAX_MTU
 #define IP_MAX_MTU			USHRT_MAX
 #endif
+#ifndef IPV6_MIN_MTU
+#define IPV6_MIN_MTU        1280
+#endif
 
 #ifndef MIN
 #define MIN(x, y)		(((x) < (y)) ? (x) : (y))
@@ -346,4 +349,7 @@ static inline int wrap_accept4(int sockfd, struct sockaddr *addr,
 #define accept4(s, addr, addrlen, flags) \
 	wrap_accept4((s), (addr), (addrlen), (flags))
 
+#define PASST_MAXDNAME 253 /* RFC 1035 */
+size_t encode_domain_name(const char* domain_name, size_t len, char* buf);
+
 #endif /* UTIL_H */
-- 
@@ -40,6 +40,9 @@
 #ifndef IP_MAX_MTU
 #define IP_MAX_MTU			USHRT_MAX
 #endif
+#ifndef IPV6_MIN_MTU
+#define IPV6_MIN_MTU        1280
+#endif
 
 #ifndef MIN
 #define MIN(x, y)		(((x) < (y)) ? (x) : (y))
@@ -346,4 +349,7 @@ static inline int wrap_accept4(int sockfd, struct sockaddr *addr,
 #define accept4(s, addr, addrlen, flags) \
 	wrap_accept4((s), (addr), (addrlen), (flags))
 
+#define PASST_MAXDNAME 253 /* RFC 1035 */
+size_t encode_domain_name(const char* domain_name, size_t len, char* buf);
+
 #endif /* UTIL_H */
-- 
2.47.0