Reference: https://src.fedoraproject.org/rpms/dhcp/blob/rawhide/f/0016-Turn-on-creating-sending-of-DUID.patch
From 0a0a7e1afa171289b9e9d855c519101bbd71b5fe Mon Sep 17 00:00:00 2001
From: Pavel Zhukov <[email protected]>
Date: Thu, 21 Feb 2019 10:36:30 +0100
Subject: [PATCH 16/28] Turn on creating/sending of DUID

as client identifier with DHCPv4 clients (#560361c#40, rfc4361)
---
 client/dhclient.c | 74 ++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 70 insertions(+), 4 deletions(-)

diff --git a/client/dhclient.c b/client/dhclient.c
index 181f6e1..444d251 100644
--- a/client/dhclient.c
+++ b/client/dhclient.c
@@ -4267,6 +4267,59 @@ write_options(struct client_state *client, struct option_state *options,
 	}
 }
 
+int unhexchar(char c) {
+
+	if (c >= '0' && c <= '9')
+		return c - '0';
+
+	if (c >= 'a' && c <= 'f')
+		return c - 'a' + 10;
+
+	if (c >= 'A' && c <= 'F')
+		return c - 'A' + 10;
+
+	return -1;
+}
+
+isc_result_t
+read_uuid(u_int8_t* uuid) {
+	const char *id_fname = "/etc/machine-id";
+	char id[32];
+	size_t nread;
+	FILE * file = fopen( id_fname , "r");
+	if (!file) {
+		log_debug("Cannot open %s", id_fname);
+		return ISC_R_IOERROR;
+	}
+	nread = fread(id, 1, sizeof id, file);
+	fclose(file);
+
+	if (nread < 32) {
+		log_debug("Not enough data in %s", id_fname);
+		return ISC_R_IOERROR;
+	}
+	int j;
+	for (j = 0; j < 16; j++) {
+		int a, b;
+
+		a = unhexchar(id[j*2]);
+		b = unhexchar(id[j*2+1]);
+
+		if (a < 0 || b < 0) {
+			log_debug("Wrong data in %s", id_fname);
+                        return ISC_R_IOERROR;
+		}
+		uuid[j] = a << 4 | b;
+	}
+
+	/* Set UUID version to 4 --- truly random generation */
+	uuid[6] = (uuid[6] & 0x0F) | 0x40;
+	/* Set the UUID variant to DCE */
+	uuid[8] = (uuid[8] & 0x3F) | 0x80;
+
+	return ISC_R_SUCCESS;
+}
+
 /*
  * The "best" default DUID, since we cannot predict any information
  * about the system (such as whether or not the hardware addresses are
@@ -4287,6 +4340,7 @@ form_duid(struct data_string *duid, const char *file, int line)
 	struct interface_info *ip;
 	int len;
 	char *str;
+	u_int8_t uuid[16];
 
 	/* For now, just use the first interface on the list. */
 	ip = interfaces;
@@ -4307,9 +4361,16 @@ form_duid(struct data_string *duid, const char *file, int line)
 	    (ip->hw_address.hlen > sizeof(ip->hw_address.hbuf)))
 		log_fatal("Impossible hardware address length at %s:%d.", MDL);
 
-	if (duid_type == 0)
-		duid_type = stateless ? DUID_LL : DUID_LLT;
-
+	if (duid_type == 0) {
+		if (read_uuid(uuid) == ISC_R_SUCCESS)
+		    duid_type = DUID_UUID;
+		else
+		    duid_type = stateless ? DUID_LL : DUID_LLT;
+	}
+	
+	if (duid_type == DUID_UUID)
+		len = 2 + sizeof (uuid);
+	else {
 	/*
 	 * 2 bytes for the 'duid type' field.
 	 * 2 bytes for the 'htype' field.
@@ -4320,13 +4381,18 @@ form_duid(struct data_string *duid, const char *file, int line)
 	len = 4 + (ip->hw_address.hlen - 1);
 	if (duid_type == DUID_LLT)
 		len += 4;
+	}
 	if (!buffer_allocate(&duid->buffer, len, MDL))
 		log_fatal("no memory for default DUID!");
 	duid->data = duid->buffer->data;
 	duid->len = len;
 
+	if (duid_type == DUID_UUID) {
+		putUShort(duid->buffer->data, DUID_UUID);
+		memcpy(duid->buffer->data + 2, uuid, sizeof(uuid));
+	}
 	/* Basic Link Local Address type of DUID. */
-	if (duid_type == DUID_LLT) {
+	else if (duid_type == DUID_LLT) {
 		putUShort(duid->buffer->data, DUID_LLT);
 		putUShort(duid->buffer->data + 2, ip->hw_address.hbuf[0]);
 		putULong(duid->buffer->data + 4, cur_time - DUID_TIME_EPOCH);
-- 
2.35.1