pimd: prevent LHR from register forwarding packets for non-FHR sources

SPT switchover handling is done by adding pimreg in the OIL of the (*, G)
entry on the LHR. This causes multicast data with that destination to be
sent to pimd as IGMPMSG_WHOLEPKT. These packets trigger creation of (S,G)
and also register forwarding. However register forwarding must only be done
if the router is also a FHR. That FHR check was missing causing strange
source registrations from multicast routers that were not directly
connected to the source.

Relevant logs from LHR -
PIM: pim_mroute_msg: pim kernel upcall WHOLEPKT type=3 ip_p=0 from fd=9 for (S,G)=(6.0.0.30,239.1.1.111) on pimreg vifi=0  size=98
PIM: Sending (6.0.0.30,239.1.1.111) Register Packet to 81.0.0.5
PIM: pim_register_send: Sending (6.0.0.30,239.1.1.111) Register Packet to 81.0.0.5 on swp2

And 6.0.0.30 is clearly not directly connected on that router -
root@tor-11:~# ip route |grep 6.0.0.30 -A2
6.0.0.30 proto ospf metric 20
	nexthop via 6.0.0.22 dev swp1 weight 1 onlink
	nexthop via 6.0.0.23 dev swp2 weight 1 onlink
root@tor-11:~#

Ticket: CM-24549

Signed-off-by: Anuradha Karuppiah <anuradhak@cumulusnetworks.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/pimd/pim_mroute.c b/pimd/pim_mroute.c
index 39ced27278..503333a206 100644
--- a/pimd/pim_mroute.c
+++ b/pimd/pim_mroute.c
@@ -323,6 +323,15 @@ static int pim_mroute_msg_wholepkt(int fd, struct interface *ifp,
 					pim_str_sg_dump(&sg));
 			return 0;
 		}
+
+		if (!PIM_UPSTREAM_FLAG_TEST_FHR(up->flags)) {
+			if (PIM_DEBUG_PIM_REG)
+				zlog_debug(
+					"%s register forward skipped, not FHR",
+					up->sg_str);
+			return 0;
+		}
+
 		pim_register_send((uint8_t *)buf + sizeof(struct ip),
 				  ntohs(ip_hdr->ip_len) - sizeof(struct ip),
 				  pim_ifp->primary_address, rpg, 0, up);