If we want to configure default routes over multiple interfaces we

need to provide the address of the interface behind which the default
router is in case they are on the same subnet otherwise the kernel
can't figure out which route we are talking about
This happens for example when your wifi and wired networks are bridged.
Pointed out by claudio some time ago.

diff --git a/sbin/dhcpleased/dhcpleased.c b/sbin/dhcpleased/dhcpleased.c
index e27a340..942ba93 100644 (file)
--- a/sbin/dhcpleased/dhcpleased.c
+++ b/sbin/dhcpleased/dhcpleased.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: dhcpleased.c,v 1.8 2021/03/16 17:39:15 florian Exp $  */
+/*     $OpenBSD: dhcpleased.c,v 1.9 2021/03/27 18:10:38 florian Exp $  */
 
 /*
  * Copyright (c) 2017, 2021 Florian Obser <florian@openbsd.org>
@@ -801,8 +801,8 @@ configure_gateway(struct imsg_configure_interface *imsg, uint8_t rtm_type)
 {
        struct rt_msghdr                 rtm;
        struct sockaddr_rtlabel          rl;
-       struct sockaddr_in               dst, gw, mask;
-       struct iovec                     iov[10];
+       struct sockaddr_in               dst, gw, mask, ifa;
+       struct iovec                     iov[12];
        long                             pad = 0;
        int                              iovcnt = 0, padlen;
 
@@ -815,7 +815,8 @@ configure_gateway(struct imsg_configure_interface *imsg, uint8_t rtm_type)
        rtm.rtm_index = imsg->if_index;
        rtm.rtm_seq = ++rtm_seq;
        rtm.rtm_priority = RTP_NONE;
-       rtm.rtm_addrs = RTA_DST | RTA_GATEWAY | RTA_NETMASK | RTA_LABEL;
+       rtm.rtm_addrs = RTA_DST | RTA_GATEWAY | RTA_NETMASK | RTA_IFA |
+           RTA_LABEL;
        rtm.rtm_flags = RTF_UP | RTF_GATEWAY | RTF_STATIC | RTF_MPATH;
 
        iov[iovcnt].iov_base = &rtm;
@@ -862,6 +863,20 @@ configure_gateway(struct imsg_configure_interface *imsg, uint8_t rtm_type)
                rtm.rtm_msglen += padlen;
        }
 
+       memset(&ifa, 0, sizeof(ifa));
+       memcpy(&ifa.sin_addr, &imsg->addr, sizeof(ifa.sin_addr));
+       ifa.sin_family = AF_INET;
+       ifa.sin_len = sizeof(struct sockaddr_in);
+       iov[iovcnt].iov_base = &ifa;
+       iov[iovcnt++].iov_len = sizeof(ifa);
+       rtm.rtm_msglen += sizeof(ifa);
+       padlen = ROUNDUP(sizeof(ifa)) - sizeof(ifa);
+       if (padlen > 0) {
+               iov[iovcnt].iov_base = &pad;
+               iov[iovcnt++].iov_len = padlen;
+               rtm.rtm_msglen += padlen;
+       }
+
        memset(&rl, 0, sizeof(rl));
        rl.sr_len = sizeof(rl);
        rl.sr_family = AF_UNSPEC;