From: David Härdeman <david@hardeman.nu>
Date: Sun, 9 Nov 2025 17:36:03 +0000 (+0100)
Subject: odhcpd: add support for "ignore"
X-Git-Url: http://git.openwrt.org/?a=commitdiff_plain;h=b6ade2ebc51419b6c4c9dc95afe35a215971ba70;p=project%2Fodhcpd.git

odhcpd: add support for "ignore"

This is inspired by @Kasoo's work in PR #234, but slightly different.

The "ip" option now takes "ignore" as a value , but it'll only disable
DHCPv4 for a matching client.

Similarly, the "hostid" option now also understands "ignore", which will
disable DHCPv6 for a matching client.

Of course, this is all based on client-reported MAC
addresses/DUIDs/client IDs/etc, so it's not actually a security feature.

Closes: https://github.com/openwrt/odhcpd/pull/234
Closes: https://github.com/openwrt/odhcpd/issues/198

Signed-off-by: David Härdeman <david@hardeman.nu>
Link: https://github.com/openwrt/odhcpd/pull/303
Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
---

diff --git a/README.md b/README.md
index b810555..1b468f9 100644
--- a/README.md
+++ b/README.md
@@ -128,10 +128,10 @@ and may also receive information from ubus
 ### Sections of type host (static leases)
 | Option		| Type	|Default| Description |
 | :-------------------- | :---- | :---- | :---------- |
-| ip			|string	|(none) | IPv4 host address |
+| ip			|string	|(none) | IPv4 host address or `ignore` to ignore any DHCPv4 request from this host |
 | mac			|list\|string|(none) | HexadecimalMACaddress(es) |
 | duid			|list\|string|(none) | Hexadecimal DUID(s), or DUID%IAID(s) |
-| hostid		|string	|(none)	| IPv6hostidentifier |
+| hostid		|string	|(none)	| IPv6 tokenised IID or `ignore` to ignore any DHCPv6 request from this host |
 | name			|string	|(none) | Hostname |
 | leasetime		|string	|(none) | DHCPv4/v6leasetime |
 
diff --git a/src/config.c b/src/config.c
index a1979a7..6130b5f 100644
--- a/src/config.c
+++ b/src/config.c
@@ -670,15 +670,26 @@ int config_set_lease_cfg_from_blobmsg(struct blob_attr *ba)
 			goto err;
 	}
 
-	if ((c = tb[LEASE_CFG_ATTR_IP]))
-		if (inet_pton(AF_INET, blobmsg_get_string(c), &lease_cfg->ipaddr) < 0)
+	if ((c = tb[LEASE_CFG_ATTR_IP])) {
+		const char *ip = blobmsg_get_string(c);
+
+		if (!strcmp(ip, "ignore"))
+			lease_cfg->ignore4 = true;
+		else if (inet_pton(AF_INET, blobmsg_get_string(c), &lease_cfg->ipaddr) < 0)
 			goto err;
+	}
 
 	if ((c = tb[LEASE_CFG_ATTR_HOSTID])) {
-		errno = 0;
-		lease_cfg->hostid = strtoull(blobmsg_get_string(c), NULL, 16);
-		if (errno)
-			goto err;
+		const char *iid = blobmsg_get_string(c);
+
+		if (!strcmp(iid, "ignore")) {
+			lease_cfg->ignore6 = true;
+		} else {
+			errno = 0;
+			lease_cfg->hostid = strtoull(blobmsg_get_string(c), NULL, 16);
+			if (errno)
+				goto err;
+		}
 	} else {
 		uint32_t i4a = ntohl(lease_cfg->ipaddr) & 0xff;
 		lease_cfg->hostid = ((i4a / 100) << 8) | (((i4a % 100) / 10) << 4) | (i4a % 10);
diff --git a/src/dhcpv4.c b/src/dhcpv4.c
index 61ec82d..49fc76c 100644
--- a/src/dhcpv4.c
+++ b/src/dhcpv4.c
@@ -534,6 +534,9 @@ dhcpv4_lease(struct interface *iface, enum dhcpv4_msg req_msg, const uint8_t *re
 	if (!lease_cfg)
 		lease_cfg = config_find_lease_cfg_by_mac(req_mac);
 
+	if (lease_cfg && lease_cfg->ignore4)
+		return NULL;
+
 	/*
 	 * If we found a static lease cfg, but no old assignment for this
 	 * hwaddr, we need to clear out any old assignments given to other
diff --git a/src/dhcpv6-ia.c b/src/dhcpv6-ia.c
index f5a22d2..de9abd9 100644
--- a/src/dhcpv6-ia.c
+++ b/src/dhcpv6-ia.c
@@ -993,6 +993,9 @@ ssize_t dhcpv6_ia_handle_IAs(uint8_t *buf, size_t buflen, struct interface *ifac
 		if (!lease_cfg)
 			lease_cfg = config_find_lease_cfg_by_mac(mac);
 
+		if (lease_cfg && lease_cfg->ignore6)
+			return -1;
+
 		/* Parse request hint for IA-PD */
 		if (is_pd) {
 			uint8_t *sdata;
diff --git a/src/odhcpd.h b/src/odhcpd.h
index 354c529..04aa7ce 100644
--- a/src/odhcpd.h
+++ b/src/odhcpd.h
@@ -302,6 +302,8 @@ struct lease_cfg {
 	struct duid *duids;
 	uint32_t leasetime;		// duration of granted leases, UINT32_MAX = inf
 	char *hostname;
+	bool ignore4;
+	bool ignore6;
 };
 
 // DNR - RFC9463