zebra: Fix to avoid two Vrfs with same table ids

During internal testing, when the following sequence is followed, two
non default vrfs end up pointing to the same table-id

 - Initially vrf201 has table id 1002
 - ip link add dev vrf202 type vrf table 1002
 - ip link set dev vrf202 up
 - ip link set dev <intrerface> master vrf202

This will ideally lead to zebra exit since this is a misconfiguration as
expected.

However if we perform a restart frr.service at this point, we end up
having two vrfs pointing to same table-id and bad things can happen.

root@mlx-3700-20:mgmt:/var/log/frr# sudo vtysh -c "sh vrf"
vrf mgmt id 37 table 1001
vrf vrf201 id 46 table 1002
vrf vrf202 id 59 table 1002 >>>>

Fix: in all cases of misconfiguration, exit zebra as expected.

Ticket :#3970414

Signed-off-by: Donald Sharp <[email protected]>

Signed-off-by: Rajasekar Raja <[email protected]>

zebra/interface.c

@@ -1483,13 +1483,17 @@ static void interface_vrf_change(enum dplane_op_e op, ifindex_t ifindex,
 				"DPLANE_OP_INTF_UPDATE for VRF %s(%u) table %u",
 				name, ifindex, tableid);
 
-		if (!vrf_lookup_by_id((vrf_id_t)ifindex)) {
-			vrf_id_t exist_id;
+		/*
+		 * For a given tableid, if there already exists a vrf and it
+		 * is different from the current vrf to be operated, then there
+		 * is a misconfiguration and zebra will exit.
+		 */
+		vrf_id_t exist_id = zebra_vrf_lookup_by_table(tableid, ns_id);
 
-			exist_id = zebra_vrf_lookup_by_table(tableid, ns_id);
-			if (exist_id != VRF_DEFAULT) {
-				vrf = vrf_lookup_by_id(exist_id);
+		if (exist_id != VRF_DEFAULT) {
+			vrf = vrf_lookup_by_id(exist_id);
 
+			if (strncmp(name, vrf->name, VRF_NAMSIZ)) {
 				if (vrf)
 					flog_err(EC_ZEBRA_VRF_MISCONFIGURED,
 						 "VRF %s id %u table id overlaps existing vrf %s(%d), misconfiguration exiting",