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

1 files changed, 14 insertions, 4 deletions

diff --git a/src/vnet/adj/adj_glean.c b/src/vnet/adj/adj_glean.c
index e956318a1ff..8df104bd19d 100644
--- a/src/vnet/adj/adj_glean.c
+++ b/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