ra: fix routing loop on point to point links

For point-to-point links (e.g. PPP) don't create a link prefix route
when receiving a prefix information option with the on-link flag set.
Point-to-point links are non shared media and as such a destination
IPv6 address cannot be on-link.
If a link prefix route points to a point-to-point link it can trigger
a routing loop if the destination IPv6 address belongs to the prefix.
If such a packet is received and not directed to a local IPv6 address
it will be routed to the point-to-point link due to the link prefix route;
the upstream ISP router will route the IPv6 packet back due to the assigned
prefix route creating a "ping pong" effect

Signed-off-by: Hans Dedecker <[email protected]>

src/ra.c

@@ -51,6 +51,7 @@
 #include "ra.h"
 
 static bool nocarrier = false;
+static bool ptp_link = false;
 
 static int sock = -1, rtnl = -1;
 static int if_index = 0;
@@ -87,6 +88,13 @@ int ra_init(const char *ifname, const struct in6_addr *ifid,
 	if (sock < 0)
 		goto failure;
 
+	memset(&ifr, 0, sizeof(ifr));
+	strncpy(ifr.ifr_name, ifname, sizeof(ifr.ifr_name) - 1);
+	if (ioctl(sock, SIOCGIFFLAGS, &ifr) < 0)
+		goto failure;
+
+	ptp_link = !!(ifr.ifr_flags & IFF_POINTOPOINT);
+
 	memset(&ifr, 0, sizeof(ifr));
 	strncpy(ifr.ifr_name, ifname, sizeof(ifr.ifr_name) - 1);
 	if (ioctl(sock, SIOCGIFINDEX, &ifr) < 0)
@@ -488,7 +496,8 @@ bool ra_process(void)
 						|| entry->valid < entry->preferred)
 					continue;
 
-				if (pinfo->nd_opt_pi_flags_reserved & ND_OPT_PI_FLAG_ONLINK)
+				if ((pinfo->nd_opt_pi_flags_reserved & ND_OPT_PI_FLAG_ONLINK) &&
+				    !ptp_link)
 					changed |= odhcp6c_update_entry(STATE_RA_ROUTE, entry,
 									7200, ra_holdoff_interval);