ipv4: Attach FIB info to dst_default_metrics when possible

If there are no explicit metrics attached to a route, hook
fi->fib_info up to dst_default_metrics.
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/dst.h

@@ -97,6 +97,7 @@ struct dst_entry {
 #ifdef __KERNEL__
 
 extern u32 *dst_cow_metrics_generic(struct dst_entry *dst, unsigned long old);
+extern const u32 dst_default_metrics[RTAX_MAX];
 
 #define DST_METRICS_READ_ONLY	0x1UL
 #define __DST_METRICS_PTR(Y)	\

net/core/dst.c

@@ -164,7 +164,7 @@ int dst_discard(struct sk_buff *skb)
 }
 EXPORT_SYMBOL(dst_discard);
 
-static const u32 dst_default_metrics[RTAX_MAX];
+const u32 dst_default_metrics[RTAX_MAX];
 
 void *dst_alloc(struct dst_ops *ops)
 {

net/ipv4/fib_semantics.c

@@ -152,7 +152,8 @@ static void free_fib_info_rcu(struct rcu_head *head)
 {
 	struct fib_info *fi = container_of(head, struct fib_info, rcu);
 
-	kfree(fi->fib_metrics);
+	if (fi->fib_metrics != (u32 *) dst_default_metrics)
+		kfree(fi->fib_metrics);
 	kfree(fi);
 }
 
@@ -743,9 +744,12 @@ struct fib_info *fib_create_info(struct fib_config *cfg)
 	fi = kzalloc(sizeof(*fi)+nhs*sizeof(struct fib_nh), GFP_KERNEL);
 	if (fi == NULL)
 		goto failure;
-	fi->fib_metrics = kzalloc(sizeof(u32) * RTAX_MAX, GFP_KERNEL);
-	if (!fi->fib_metrics)
-		goto failure;
+	if (cfg->fc_mx) {
+		fi->fib_metrics = kzalloc(sizeof(u32) * RTAX_MAX, GFP_KERNEL);
+		if (!fi->fib_metrics)
+			goto failure;
+	} else
+		fi->fib_metrics = (u32 *) dst_default_metrics;
 	fib_info_cnt++;
 
 	fi->fib_net = hold_net(net);