Make sure the interface still exists before updating it.

When we get a route message, for example an address being added
(RTM_NEWADDR, but the problem exists with most of the route messages)
and the interface gets unplugged at just the right moment
if_nametoindex(3) will return NULL. We will pass NULL through
update_iface() to get_xflags() which will then crash because we
dereference the NULL pointer there.

OK kn

diff --git a/sbin/slaacd/frontend.c b/sbin/slaacd/frontend.c
index dc5cb82..7ebc92b 100644 (file)
--- a/sbin/slaacd/frontend.c
+++ b/sbin/slaacd/frontend.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: frontend.c,v 1.59 2021/11/28 12:49:55 florian Exp $   */
+/*     $OpenBSD: frontend.c,v 1.60 2021/11/28 12:51:52 florian Exp $   */
 
 /*
  * Copyright (c) 2017 Florian Obser <florian@openbsd.org>
@@ -830,6 +830,14 @@ handle_route_message(struct rt_msghdr *rtm, struct sockaddr **rti_info)
                ifm = (struct if_msghdr *)rtm;
                if_index = ifm->ifm_index;
                if_name = if_indextoname(if_index, ifnamebuf);
+               if (if_name == NULL) {
+                       log_debug("RTM_NEWADDR: lost if %d", if_index);
+                       frontend_imsg_compose_engine(IMSG_REMOVE_IF, 0, 0,
+                           &if_index, sizeof(if_index));
+                       remove_iface(if_index);
+                       break;
+               }
+
                log_debug("RTM_NEWADDR: %s[%u]", if_name, if_index);
                update_iface(if_index, if_name);
                break;
@@ -837,6 +845,13 @@ handle_route_message(struct rt_msghdr *rtm, struct sockaddr **rti_info)
                ifm = (struct if_msghdr *)rtm;
                if_index = ifm->ifm_index;
                if_name = if_indextoname(if_index, ifnamebuf);
+               if (if_name == NULL) {
+                       log_debug("RTM_DELADDR: lost if %d", if_index);
+                       frontend_imsg_compose_engine(IMSG_REMOVE_IF, 0, 0,
+                           &if_index, sizeof(if_index));
+                       remove_iface(if_index);
+                       break;
+               }
                if (rtm->rtm_addrs & RTA_IFA && rti_info[RTAX_IFA]->sa_family
                    == AF_INET6) {
                        del_addr.if_index = if_index;
@@ -851,6 +866,13 @@ handle_route_message(struct rt_msghdr *rtm, struct sockaddr **rti_info)
                ifm = (struct if_msghdr *)rtm;
                if_index = ifm->ifm_index;
                if_name = if_indextoname(if_index, ifnamebuf);
+               if (if_name == NULL) {
+                       log_debug("RTM_CHGADDRATTR: lost if %d", if_index);
+                       frontend_imsg_compose_engine(IMSG_REMOVE_IF, 0, 0,
+                           &if_index, sizeof(if_index));
+                       remove_iface(if_index);
+                       break;
+               }
                if (rtm->rtm_addrs & RTA_IFA && rti_info[RTAX_IFA]->sa_family
                    == AF_INET6) {
                        sin6 = (struct sockaddr_in6 *) rti_info[RTAX_IFA];
@@ -904,6 +926,13 @@ handle_route_message(struct rt_msghdr *rtm, struct sockaddr **rti_info)
                        break;
                if_index = ifm->ifm_index;
                if_name = if_indextoname(if_index, ifnamebuf);
+               if (if_name == NULL) {
+                       log_debug("RTM_DELETE: lost if %d", if_index);
+                       frontend_imsg_compose_engine(IMSG_REMOVE_IF, 0, 0,
+                           &if_index, sizeof(if_index));
+                       remove_iface(if_index);
+                       break;
+               }
 
                del_route.if_index = if_index;
                memcpy(&del_route.gw, rti_info[RTAX_GATEWAY],