From 6329e37d595d6fd6b2c40951ca6774a702c250d8 Mon Sep 17 00:00:00 2001
From: =?utf8?q?David=20H=C3=A4rdeman?= <david@hardeman.nu>
Date: Mon, 6 Oct 2025 12:23:18 +0200
Subject: [PATCH] dhcpv4: use iovec for NTP
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Note that the previous code would send out several NTP options if
the client requested the option more than once, and would also send
out zero-sized options (against RFC2132, §8.3).

Signed-off-by: David Härdeman <david@hardeman.nu>
Link: https://github.com/openwrt/odhcpd/pull/278
Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
---
 src/dhcpv4.c | 22 ++++++++++++++++------
 src/dhcpv4.h |  2 +-
 2 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/src/dhcpv4.c b/src/dhcpv4.c
index 7201c4a..62f6853 100644
--- a/src/dhcpv4.c
+++ b/src/dhcpv4.c
@@ -621,6 +621,8 @@ enum {
 	IOV_HEADER = 0,
 	IOV_MESSAGE,
 	IOV_SERVERID,
+	IOV_NTP,
+	IOV_NTP_ADDR,
 	IOV_END,
 	IOV_TOTAL
 };
@@ -664,13 +666,19 @@ void dhcpv4_handle_msg(void *src_addr, void *data, size_t len,
 		.len = sizeof(struct in_addr),
 		.data = iface->dhcpv4_local.s_addr,
 	};
+	struct dhcpv4_option reply_ntp = {
+		.code = DHCPV4_OPT_NTPSERVER,
+		.len = iface->dhcpv4_ntp_cnt * sizeof(*iface->dhcpv4_ntp),
+	};
 	uint8_t reply_end = DHCPV4_OPT_END;
 
 	struct iovec iov[IOV_TOTAL] = {
-		[IOV_HEADER] = { &reply, 0 },
-		[IOV_MESSAGE] = { &reply_msg, sizeof(reply_msg) },
-		[IOV_SERVERID] = { &reply_serverid, sizeof(reply_serverid) },
-		[IOV_END] = { &reply_end, sizeof(reply_end) },
+		[IOV_HEADER]	= { &reply, 0 },
+		[IOV_MESSAGE]	= { &reply_msg, sizeof(reply_msg) },
+		[IOV_SERVERID]	= { &reply_serverid, sizeof(reply_serverid) },
+		[IOV_NTP]	= { &reply_ntp, 0 },
+		[IOV_NTP_ADDR]	= { iface->dhcpv4_ntp, 0 },
+		[IOV_END]	= { &reply_end, sizeof(reply_end) },
 	};
 
 	/* Misc */
@@ -905,8 +913,10 @@ void dhcpv4_handle_msg(void *src_addr, void *data, size_t len,
 	for (size_t opt = 0; a && opt < req_opts_len; opt++) {
 		switch (req_opts[opt]) {
 		case DHCPV4_OPT_NTPSERVER:
-			dhcpv4_put(&reply, &cursor, DHCPV4_OPT_NTPSERVER,
-				   4 * iface->dhcpv4_ntp_cnt, iface->dhcpv4_ntp);
+			if (!a)
+				break;
+			iov[IOV_NTP].iov_len = sizeof(reply_ntp);
+			iov[IOV_NTP_ADDR].iov_len = iface->dhcpv4_ntp_cnt * sizeof(*iface->dhcpv4_ntp);
 			break;
 
 		case DHCPV4_OPT_DNR:
diff --git a/src/dhcpv4.h b/src/dhcpv4.h
index f96e5bf..089a626 100644
--- a/src/dhcpv4.h
+++ b/src/dhcpv4.h
@@ -151,7 +151,7 @@ struct dhcpv4_option_u32 {
 	uint8_t code;
 	uint8_t len;
 	uint32_t data;
-};
+} _packed;
 
 /* DNR */
 struct dhcpv4_dnr {
-- 
2.30.2