From cc3ec9c20c61904b8ebb41593d6814a0f54b6dc4 Mon Sep 17 00:00:00 2001
From: =?utf8?q?David=20H=C3=A4rdeman?= <david@hardeman.nu>
Date: Sat, 20 Sep 2025 18:19:06 +0200
Subject: [PATCH] odhcpd: support IAIDs for static DHCPv6 leases
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Extend the string format for duids to alternatively support
"<duid>%<iaid>", which makes it possible to define separate static
leases, e.g. for a client which is connected to the same network with
more than one interface (which will both have the same DUID, as it is a
per-host identifier, but different IAIDs).

Note that this only wires up the new format, actually using it to make
DHCPv6-IA decisions will be implemented in subsequent patches.

Signed-off-by: David Härdeman <david@hardeman.nu>
Link: https://github.com/openwrt/odhcpd/pull/255
Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
---
 README.md    |  2 +-
 src/config.c | 52 ++++++++++++++++++++++++++++++++++++++++++++--------
 src/odhcpd.h |  4 ++++
 3 files changed, 49 insertions(+), 9 deletions(-)

diff --git a/README.md b/README.md
index b710b93..69d7a6c 100644
--- a/README.md
+++ b/README.md
@@ -125,7 +125,7 @@ and may also receive information from ubus
 | :-------------------- | :---- | :---- | :---------- |
 | ip			|string	|(none) | IPv4 host address |
 | mac			|list\|string|(none) | HexadecimalMACaddress(es) |
-| duid			|string	|(none)	| HexadecimalDUID |
+| duid			|string |(none) | Hexadecimal DUID, or DUID%IAID |
 | hostid		|string	|(none)	| IPv6hostidentifier |
 | name			|string	|(none) | Hostname |
 | leasetime		|string	|(none) | DHCPv4/v6leasetime |
diff --git a/src/config.c b/src/config.c
index 0dcef1b..5f072ea 100644
--- a/src/config.c
+++ b/src/config.c
@@ -469,7 +469,7 @@ int set_lease_from_blobmsg(struct blob_attr *ba)
 	struct lease *l = NULL;
 	int mac_count = 0;
 	struct ether_addr *macs;
-	size_t duidlen = 0;
+	size_t duid_alloc_size = 0;
 	uint8_t *duid;
 
 	blobmsg_parse(lease_attrs, LEASE_ATTR_MAX, tb, blob_data(ba), blob_len(ba));
@@ -481,11 +481,12 @@ int set_lease_from_blobmsg(struct blob_attr *ba)
 	}
 
 	if ((c = tb[LEASE_ATTR_DUID]))
-		duidlen = (blobmsg_data_len(c) - 1) / 2;
+		/* We might overallocate some bytes here, that's fine */
+		duid_alloc_size = (blobmsg_data_len(c) - 1) / 2;
 
 	l = calloc_a(sizeof(*l),
 		     &macs, mac_count * sizeof(*macs),
-		     &duid, duidlen);
+		     &duid, duid_alloc_size);
 	if (!l)
 		goto err;
 
@@ -503,15 +504,50 @@ int set_lease_from_blobmsg(struct blob_attr *ba)
 	}
 
 	if ((c = tb[LEASE_ATTR_DUID])) {
-		ssize_t len;
+		const char *duid_str = blobmsg_get_string(c);
+		size_t duid_str_len = blobmsg_data_len(c) - 1;
+		ssize_t duid_len;
+		const char *iaid_str;
+
+		/* We support a hex string with either "<DUID>", or "<DUID>%<IAID>" */
+		iaid_str = strrchr(duid_str, '%');
+		if (iaid_str) {
+			size_t iaid_str_len = strlen(++iaid_str);
+
+			/* IAID = uint32, RFC8415, §21.4, §21.5, §21.21 */
+			if (iaid_str_len < 1 || iaid_str_len > 2 * sizeof(uint32_t)) {
+				syslog(LOG_ERR, "Invalid IAID length '%s'", iaid_str);
+				goto err;
+			}
 
-		l->duid = duid;
-		len = odhcpd_unhexlify(l->duid, duidlen, blobmsg_get_string(c));
+			errno = 0;
+			l->iaid = strtoull(iaid_str, NULL, 16);
+			if (errno) {
+				syslog(LOG_ERR, "Invalid IAID '%s'", iaid_str);
+				goto err;
+			}
+
+			l->iaid_set = true;
+			duid_str_len -= (iaid_str_len + 1);
+		}
+
+		if (duid_str_len < 2 || duid_str_len > DUID_MAX_LEN * 2 || duid_str_len % 2) {
+			syslog(LOG_ERR, "Invalid DUID length '%.*s'", (int)duid_str_len, duid_str);
+			goto err;
+		}
 
-		if (len < 0)
+		l->duid = duid;
+		duid_len = odhcpd_unhexlify(l->duid, duid_str_len / 2, duid_str);
+		if (duid_len < 0) {
+			syslog(LOG_ERR, "Invalid DUID '%.*s'", (int)duid_str_len, duid_str);
 			goto err;
+		}
 
-		l->duid_len = len;
+		l->duid_len = duid_len;
+		syslog(LOG_DEBUG,
+		       "Found a static lease for DUID '%.*s' (%zi bytes), IAID 0x%08" PRIx32 "%s",
+		       (int)duid_str_len, duid_str, duid_len,
+		       l->iaid, l->iaid_set ? "" : " (not defined)");
 	}
 
 	if ((c = tb[LEASE_ATTR_NAME])) {
diff --git a/src/odhcpd.h b/src/odhcpd.h
index 0903487..e225108 100644
--- a/src/odhcpd.h
+++ b/src/odhcpd.h
@@ -180,6 +180,8 @@ struct config {
 	int log_level;
 };
 
+/* 2-byte type + 128-byte DUID, RFC8415, §11.1 */
+#define DUID_MAX_LEN 130
 
 struct lease {
 	struct vlist_node node;
@@ -190,6 +192,8 @@ struct lease {
 	struct ether_addr *macs;
 	uint16_t duid_len;
 	uint8_t *duid;
+	uint32_t iaid;
+	bool iaid_set;
 	uint32_t leasetime;
 	char *hostname;
 };
-- 
2.30.2