From 288abd9c40461a00d6a52b40153fbf13c423bc1f Mon Sep 17 00:00:00 2001
From: Paul Donald <newtwen+github@gmail.com>
Date: Sun, 19 Oct 2025 19:30:38 +0200
Subject: [PATCH] dhcpv6: move dhcpv6 message type check for early exit
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Avoid doing a bunch of work if the message type we received is not a
client type and does not warrant a reply. Exit early.

Clarify and comment message type handling.

Signed-off-by: Paul Donald <newtwen+github@gmail.com>
Link: https://github.com/openwrt/odhcpd/pull/279
Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
---
 src/dhcpv6.c | 56 ++++++++++++++++++++++++++++------------------------
 src/dhcpv6.h |  2 ++
 2 files changed, 32 insertions(+), 26 deletions(-)

diff --git a/src/dhcpv6.c b/src/dhcpv6.c
index 73ce0b3..b92790e 100644
--- a/src/dhcpv6.c
+++ b/src/dhcpv6.c
@@ -318,6 +318,36 @@ static void handle_client_request(void *addr, void *data, size_t len,
 	if (len < sizeof(*hdr))
 		return;
 
+	switch (hdr->msg_type) {
+	/* Valid message types for clients */
+	case DHCPV6_MSG_SOLICIT:
+	case DHCPV6_MSG_REQUEST:
+	case DHCPV6_MSG_CONFIRM:
+	case DHCPV6_MSG_RENEW:
+	case DHCPV6_MSG_REBIND:
+	case DHCPV6_MSG_RELEASE:
+	case DHCPV6_MSG_DECLINE:
+	case DHCPV6_MSG_INFORMATION_REQUEST:
+	case DHCPV6_MSG_RELAY_FORW:
+#ifdef DHCPV4_SUPPORT
+	/* if we include DHCPV4 support, handle this message type */
+	case DHCPV6_MSG_DHCPV4_QUERY:
+#endif
+		break;
+	/* Invalid message types for clients i.e. server messages */
+	case DHCPV6_MSG_ADVERTISE:
+	case DHCPV6_MSG_REPLY:
+	case DHCPV6_MSG_RECONFIGURE:
+	case DHCPV6_MSG_RELAY_REPL:
+#ifndef DHCPV4_SUPPORT
+	/* if we omit DHCPV4 support, ignore this client message type */
+	case DHCPV6_MSG_DHCPV4_QUERY:
+#endif
+	case DHCPV6_MSG_DHCPV4_RESPONSE:
+	default:
+		return;
+	}
+
 	debug("Got a DHCPv6-request on %s", iface->name);
 
 	/* Construct reply message */
@@ -566,32 +596,6 @@ static void handle_client_request(void *addr, void *data, size_t len,
 	if (hdr->msg_type == DHCPV6_MSG_RELAY_FORW)
 		handle_nested_message(data, len, &hdr, &opts, &opts_end, iov);
 
-	switch (hdr->msg_type) {
-	case DHCPV6_MSG_SOLICIT:
-	case DHCPV6_MSG_REQUEST:
-	case DHCPV6_MSG_CONFIRM:
-	case DHCPV6_MSG_RENEW:
-	case DHCPV6_MSG_REBIND:
-	case DHCPV6_MSG_RELEASE:
-	case DHCPV6_MSG_DECLINE:
-	case DHCPV6_MSG_INFORMATION_REQUEST:
-	case DHCPV6_MSG_RELAY_FORW:
-#ifdef DHCPV4_SUPPORT
-	case DHCPV6_MSG_DHCPV4_QUERY:
-#endif
-		break; /* Valid message types for clients */
-	case DHCPV6_MSG_ADVERTISE:
-	case DHCPV6_MSG_REPLY:
-	case DHCPV6_MSG_RECONFIGURE:
-	case DHCPV6_MSG_RELAY_REPL:
-	case DHCPV6_MSG_DHCPV4_RESPONSE:
-#ifndef DHCPV4_SUPPORT
-	case DHCPV6_MSG_DHCPV4_QUERY:
-#endif
-	default:
-		return; /* Invalid message types for clients */
-	}
-
 	if (!IN6_IS_ADDR_MULTICAST((struct in6_addr *)dest_addr) && iov[IOV_NESTED].iov_len == 0 &&
 	    (hdr->msg_type == DHCPV6_MSG_SOLICIT || hdr->msg_type == DHCPV6_MSG_CONFIRM ||
 	     hdr->msg_type == DHCPV6_MSG_REBIND || hdr->msg_type == DHCPV6_MSG_INFORMATION_REQUEST))
diff --git a/src/dhcpv6.h b/src/dhcpv6.h
index a394453..4220fe2 100644
--- a/src/dhcpv6.h
+++ b/src/dhcpv6.h
@@ -22,6 +22,7 @@
 #define DHCPV6_CLIENT_PORT 546
 #define DHCPV6_SERVER_PORT 547
 
+/* RFC8415 */
 #define DHCPV6_MSG_SOLICIT 1
 #define DHCPV6_MSG_ADVERTISE 2
 #define DHCPV6_MSG_REQUEST 3
@@ -35,6 +36,7 @@
 #define DHCPV6_MSG_INFORMATION_REQUEST 11
 #define DHCPV6_MSG_RELAY_FORW 12
 #define DHCPV6_MSG_RELAY_REPL 13
+/* RFC7341 */
 #define DHCPV6_MSG_DHCPV4_QUERY 20
 #define DHCPV6_MSG_DHCPV4_RESPONSE 21
 
-- 
2.30.2