fib: fix sa selection for fib routed destinations

The move from ip4(6)_src_address_for_packet to fib_sas4(6)_get changed
the behavior, so that the new looked only to adjacent gleans. This
caused a problem for destinations routed according to FIB table.

To reproduce:
vpp# create tap
vpp# set interface state tap0 up
vpp# set interface ip address tap0 192.168.11.1/24
vpp# ip route add 192.168.20.0/24 via 192.168.11.2

linux$ sudo ip addr add 192.168.20.1/24 dev lo
linux$ sudo ip link set tap0 up
linux$ sudo ip addr add 192.168.11.2/24 dev tap0

vpp# ping 192.168.20.1
Failed: no source address for egress interface

Type: fix
Signed-off-by: Július Milan <julius.milan@pantheon.tech>
Signed-off-by: Neale Ranns <neale@graphiant.com>
Change-Id: I22899f4dbbf8c1c85ccce72f801b92c183195b5d
(cherry picked from commit 98874cda5853ea2d6b2dc32001b935d394b88430)

src/vnet/adj/adj_glean.c

@@ -258,8 +258,8 @@ adj_glean_get_src (fib_protocol_t proto,
                    u32 sw_if_index,
                    const ip46_address_t *nh)
 {
+    const ip46_address_t *conn, *source;
     const ip_adjacency_t *adj;
-    ip46_address_t *conn;
     adj_index_t ai;
 
     if (vec_len(adj_gleans[proto]) <= sw_if_index ||
@@ -274,23 +274,33 @@ adj_glean_get_src (fib_protocol_t proto,
     if (nh)
         pfx.fp_addr = *nh;
 
+    /*
+     * An interface can have more than one glean address. Where
+     * possible we want to return a source address from the same
+     * subnet as the destination. If this is not possible then any address
+     * will do.
+     */
+    source = NULL;
+
     hash_foreach_mem(conn, ai, adj_gleans[proto][sw_if_index],
     ({
         adj = adj_get(ai);
 
         if (adj->sub_type.glean.rx_pfx.fp_len > 0)
         {
+            source = &adj->sub_type.glean.rx_pfx.fp_addr;
+
             /* if no destination is specified use the just glean */
             if (NULL == nh)
-                return (&adj->sub_type.glean.rx_pfx.fp_addr);
+                return (source);
 
             /* check the clean covers the desintation */
             if (fib_prefix_is_cover(&adj->sub_type.glean.rx_pfx, &pfx))
-                return (&adj->sub_type.glean.rx_pfx.fp_addr);
+                return (source);
         }
     }));
 
-    return (NULL);
+    return (source);
 }
 
 void

test/test_ping.py

@@ -7,7 +7,7 @@ from scapy.packet import Raw
 
 from framework import VppTestCase
 from util import ppp
-from vpp_ip_route import VppIpInterfaceAddress
+from vpp_ip_route import VppIpInterfaceAddress, VppIpRoute, VppRoutePath
 from vpp_neighbor import VppNeighbor
 
 """ TestPing is a subclass of  VPPTestCase classes.
@@ -150,3 +150,27 @@ class TestPing(VppTestCase):
         for p in out:
             icmp = self.verify_ping_request(p, "10.0.0.1", nbr_addr, icmp_seq)
             icmp_seq = icmp_seq + 1
+
+    def test_ping_fib_routed_dst(self):
+        """ ping destination routed according to FIB table """
+
+        try:
+            self.pg1.generate_remote_hosts(1)
+            self.pg_enable_capture(self.pg_interfaces)
+            self.pg_start()
+            routed_dst = "10.0.2.0"
+            self.logger.info(self.vapi.cli("show ip4 neighbors"))
+            VppIpRoute(self, routed_dst, 24,
+                       [VppRoutePath(self.pg1.remote_hosts[0].ip4,
+                                     self.pg1.sw_if_index)]).add_vpp_config()
+            ping_cmd = "ping %s interval 0.01 repeat 3" % routed_dst
+            ret = self.vapi.cli(ping_cmd)
+            self.logger.info(ret)
+            out = self.pg1.get_capture(3)
+            icmp_seq = 1
+            for p in out:
+                self.verify_ping_request(p, self.pg1.local_ip4, routed_dst,
+                                         icmp_seq)
+                icmp_seq = icmp_seq + 1
+        finally:
+            self.vapi.cli("show error")