ipv4: fix the reusing of routing cache entries

compare_keys and ip_route_input_common rely on
rt_oif for distinguishing of input and output routes
with same keys values. But sometimes the input route has
also same hash chain (keyed by iif != 0) with the output
routes (keyed by orig_oif=0). Problem visible if running
with small number of rhash_entries.

	Fix them to use rt_route_iif instead. By this way
input route can not be returned to users that request
output route.

	The patch fixes the ip_rt_bug errors that were
reported in ip_local_out context, mostly for 255.255.255.255
destinations.

Signed-off-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/route.c

@@ -731,6 +731,7 @@ static inline int compare_keys(struct rtable *rt1, struct rtable *rt2)
 		((__force u32)rt1->rt_key_src ^ (__force u32)rt2->rt_key_src) |
 		(rt1->rt_mark ^ rt2->rt_mark) |
 		(rt1->rt_key_tos ^ rt2->rt_key_tos) |
+		(rt1->rt_route_iif ^ rt2->rt_route_iif) |
 		(rt1->rt_oif ^ rt2->rt_oif) |
 		(rt1->rt_iif ^ rt2->rt_iif)) == 0;
 }
@@ -2321,8 +2322,8 @@ int ip_route_input_common(struct sk_buff *skb, __be32 daddr, __be32 saddr,
 		if ((((__force u32)rth->rt_key_dst ^ (__force u32)daddr) |
 		     ((__force u32)rth->rt_key_src ^ (__force u32)saddr) |
 		     (rth->rt_iif ^ iif) |
-		     rth->rt_oif |
 		     (rth->rt_key_tos ^ tos)) == 0 &&
+		    rt_is_input_route(rth) &&
 		    rth->rt_mark == skb->mark &&
 		    net_eq(dev_net(rth->dst.dev), net) &&
 		    !rt_is_expired(rth)) {