From: Paul Donald <newtwen+github@gmail.com>
Date: Thu, 30 Oct 2025 00:52:20 +0000 (+0100)
Subject: config: clamp ra_mtu to interface MTU, and default ra_mtu to interface MTU
X-Git-Url: http://git.openwrt.org/%22https:/collectd.org//%22/%22https:/collectd.org/%22?a=commitdiff_plain;h=1480c09ee0aaca2d00db74af6b5f468cb409e064;p=project%2Fodhcpd.git

config: clamp ra_mtu to interface MTU, and default ra_mtu to interface MTU

Set ra_mtu max to that of its interface. We also default ra_mtu if the user
did not configure it.

Signed-off-by: Paul Donald <newtwen+github@gmail.com>
Link: https://github.com/openwrt/odhcpd/pull/296
Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
---

diff --git a/src/config.c b/src/config.c
index 654c329..a54c64c 100644
--- a/src/config.c
+++ b/src/config.c
@@ -1504,6 +1504,7 @@ int config_parse_interface(void *data, size_t len, const char *name, bool overwr
 
 	}
 
+	iface->if_mtu = odhcpd_get_interface_config(iface->ifname, "mtu");
 	if ((c = tb[IFACE_ATTR_RA_MTU])) {
 		uint32_t original_ra_mtu, ra_mtu;
 		original_ra_mtu = ra_mtu = blobmsg_get_u32(c);
@@ -1511,6 +1512,9 @@ int config_parse_interface(void *data, size_t len, const char *name, bool overwr
 			ra_mtu = RA_MTU_MIN;
 		else if (ra_mtu > RA_MTU_MAX)
 			ra_mtu = RA_MTU_MAX;
+		if (iface->if_mtu && ra_mtu > iface->if_mtu)
+			ra_mtu = iface->if_mtu;
+
 		iface->ra_mtu = ra_mtu;
 
 		if (original_ra_mtu != ra_mtu) {
@@ -1519,6 +1523,13 @@ int config_parse_interface(void *data, size_t len, const char *name, bool overwr
 		}
 	}
 
+	/* Default RA MTU to the interface MTU if no value is assigned */
+	if (!iface->ra_mtu && iface->if_mtu) {
+		iface->ra_mtu = iface->if_mtu;
+		info("Defaulted %s value for interface '%s' to %d",
+		     iface_attrs[IFACE_ATTR_RA_MTU].name, iface->name, iface->ra_mtu);
+	}
+
 	if ((c = tb[IFACE_ATTR_RA_SLAAC]))
 		iface->ra_slaac = blobmsg_get_bool(c);