From ab2d7cdfa4bf8c0f4e11a687e48f871879cdfbd3 Mon Sep 17 00:00:00 2001
From: Roy Marples <roy@marples.name>
Date: Mon, 17 Feb 2025 15:01:45 +0000
Subject: [PATCH] For route MTU comparison allow zero MTU to match interface
 MTU

Because some OS put the interface MTU into the route MTU if the
route does not define its own.
---
 src/dhcpcd.h   |  1 +
 src/if-bsd.c   |  1 +
 src/if-linux.c | 10 ++++++++--
 src/if-sun.c   |  1 +
 src/if.c       | 13 +++++++++++++
 src/if.h       |  1 +
 src/route.c    | 12 +++++++++++-
 7 files changed, 36 insertions(+), 3 deletions(-)

diff --git a/src/dhcpcd.h b/src/dhcpcd.h
index 17aa8d96..074ae1ca 100644
--- a/src/dhcpcd.h
+++ b/src/dhcpcd.h
@@ -80,6 +80,7 @@ struct interface {
 	uint16_t hwtype; /* ARPHRD_ETHER for example */
 	unsigned char hwaddr[HWADDR_LEN];
 	uint8_t hwlen;
+	unsigned int mtu;
 	unsigned short vlanid;
 	unsigned int metric;
 	int carrier;
diff --git a/src/if-bsd.c b/src/if-bsd.c
index d184ef84..8af59610 100644
--- a/src/if-bsd.c
+++ b/src/if-bsd.c
@@ -1252,6 +1252,7 @@ if_ifinfo(struct dhcpcd_ctx *ctx, const struct if_msghdr *ifm)
 	if ((ifp = if_findindex(ctx->ifaces, ifm->ifm_index)) == NULL)
 		return 0;
 
+	ifp->mtu = if_mtu(ifp);
 	link_state = if_carrier(ifp, &ifm->ifm_data);
 	dhcpcd_handlecarrier(ifp, link_state, (unsigned int)ifm->ifm_flags);
 	return 0;
diff --git a/src/if-linux.c b/src/if-linux.c
index b6317c35..2a105a11 100644
--- a/src/if-linux.c
+++ b/src/if-linux.c
@@ -1053,7 +1053,7 @@ link_netlink(struct dhcpcd_ctx *ctx, void *arg, struct nlmsghdr *nlm)
 	struct interface *ifp = arg;
 	int r;
 	size_t len;
-	struct rtattr *rta, *hwaddr;
+	struct rtattr *rta, *hwaddr, *mtu;
 	struct ifinfomsg *ifi;
 	char ifn[IF_NAMESIZE + 1];
 
@@ -1082,7 +1082,7 @@ link_netlink(struct dhcpcd_ctx *ctx, void *arg, struct nlmsghdr *nlm)
 	rta = (void *)((char *)ifi + NLMSG_ALIGN(sizeof(*ifi)));
 	len = NLMSG_PAYLOAD(nlm, sizeof(*ifi));
 	*ifn = '\0';
-	hwaddr = NULL;
+	hwaddr = mtu = NULL;
 
 	for (; RTA_OK(rta, len); rta = RTA_NEXT(rta, len)) {
 		switch (rta->rta_type) {
@@ -1098,6 +1098,9 @@ link_netlink(struct dhcpcd_ctx *ctx, void *arg, struct nlmsghdr *nlm)
 		case IFLA_ADDRESS:
 			hwaddr = rta;
 			break;
+		case IFLA_MTU:
+			mtu = rta;
+			break;
 		}
 	}
 
@@ -1139,6 +1142,9 @@ link_netlink(struct dhcpcd_ctx *ctx, void *arg, struct nlmsghdr *nlm)
 		return 0;
 	}
 
+	if (mtu != NULL)
+		ifp->mtu = *(unsigned int *)RTA_DATA(mtu);
+
 	/* Re-read hardware address and friends */
 	if (!(ifi->ifi_flags & IFF_UP)) {
 		void *hwa = hwaddr != NULL ? RTA_DATA(hwaddr) : NULL;
diff --git a/src/if-sun.c b/src/if-sun.c
index 7f244b77..cb4849b4 100644
--- a/src/if-sun.c
+++ b/src/if-sun.c
@@ -1059,6 +1059,7 @@ if_ifinfo(struct dhcpcd_ctx *ctx, const struct if_msghdr *ifm)
 		state = LINK_UP;
 		flags |= IFF_UP;
 	}
+	ifp->mtu = if_mtu(ifp);
 	dhcpcd_handlecarrier(ifp, state, flags);
 	return 0;
 }
diff --git a/src/if.c b/src/if.c
index dea833df..69c2c4c1 100644
--- a/src/if.c
+++ b/src/if.c
@@ -182,6 +182,18 @@ if_setflag(struct interface *ifp, short setflag, short unsetflag)
 	return 0;
 }
 
+unsigned int
+if_mtu(struct interface *ifp)
+{
+	struct ifreq ifr = { .ifr_mtu = 0 };
+
+	strlcpy(ifr.ifr_name, ifp->name, sizeof(ifr.ifr_name));
+	if (ioctl(ifp->ctx->pf_inet_fd, SIOCGIFMTU, &ifr) == -1)
+		return 0;
+
+	return (unsigned int)ifr.ifr_mtu;
+}
+
 bool
 if_is_link_up(const struct interface *ifp)
 {
@@ -685,6 +697,7 @@ if_discover(struct dhcpcd_ctx *ctx, struct ifaddrs **ifaddrs,
 			}
 		}
 
+		ifp->mtu = if_mtu(ifp);
 		ifp->vlanid = if_vlanid(ifp);
 
 #ifdef SIOCGIFPRIORITY
diff --git a/src/if.h b/src/if.h
index 6cb9d766..1872a37b 100644
--- a/src/if.h
+++ b/src/if.h
@@ -163,6 +163,7 @@ int if_ioctl(struct dhcpcd_ctx *, ioctl_request_t, void *, size_t);
 #define	pioctl(ctx, req, data, len) ioctl((ctx)->pf_inet_fd, (req),(data),(len))
 #endif
 int if_setflag(struct interface *, short, short);
+unsigned int if_mtu(struct interface *);
 #define if_up(ifp) if_setflag((ifp), (IFF_UP | IFF_RUNNING), 0)
 #define if_down(ifp) if_setflag((ifp), 0, IFF_UP);
 bool if_is_link_up(const struct interface *);
diff --git a/src/route.c b/src/route.c
index d56b9d30..bbc7bfd7 100644
--- a/src/route.c
+++ b/src/route.c
@@ -506,9 +506,19 @@ rt_recvrt(int cmd, const struct rt *rt, pid_t pid)
 static bool
 rt_cmp_misc(struct rt *nrt, struct rt *ort)
 {
-	/* MTU changed */
+#if defined(__FreeBSD__) || defined(__DragonFly__)
+	/* FreeBSD puts the interface MTU into the route MTU
+	 * if the route does not define it's own. */
+	unsigned int nmtu, omtu;
+
+	nmtu = nrt->rt_mtu ? nrt->rt_mtu : nrt->rt_ifp->mtu;
+	omtu = ort->rt_mtu ? ort->rt_mtu : ort->rt_ifp->mtu;
+	if (omtu != nmtu)
+		return false;
+#else
 	if (ort->rt_mtu != nrt->rt_mtu)
 		return false;
+#endif
 
 #ifdef HAVE_ROUTE_LIFETIME
 	uint32_t deviation;
-- 
2.47.2