ipv6: fix memory leak with multiple tables during netns destruction

fib6_net_exit only frees the main and local tables. If another table was
created with fib6_alloc_table, we leak it when the netns is destroyed.

Fix this in the same way ip_fib_net_exit cleans up tables, by walking
through the whole hashtable of fib6_table's. We can get rid of the
special cases for local and main, since they're also part of the
hashtable.

Reproducer:
    ip netns add x
    ip -net x -6 rule add from 6003:1::/64 table 100
    ip netns del x
Reported-by: NJianlin Shi <jishi@redhat.com>
Fixes: 58f09b78 ("[NETNS][IPV6] ip6_fib - make it per network namespace")
Signed-off-by: NSabrina Dubroca <sd@queasysnail.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv6/ip6_fib.c

@@ -191,6 +191,12 @@ void rt6_free_pcpu(struct rt6_info *non_pcpu_rt)
 }
 EXPORT_SYMBOL_GPL(rt6_free_pcpu);
 
+static void fib6_free_table(struct fib6_table *table)
+{
+	inetpeer_invalidate_tree(&table->tb6_peers);
+	kfree(table);
+}
+
 static void fib6_link_table(struct net *net, struct fib6_table *tb)
 {
 	unsigned int h;
@@ -2022,15 +2028,22 @@ static int __net_init fib6_net_init(struct net *net)
 
 static void fib6_net_exit(struct net *net)
 {
+	unsigned int i;
+
 	rt6_ifdown(net, NULL);
 	del_timer_sync(&net->ipv6.ip6_fib_timer);
 
-#ifdef CONFIG_IPV6_MULTIPLE_TABLES
-	inetpeer_invalidate_tree(&net->ipv6.fib6_local_tbl->tb6_peers);
-	kfree(net->ipv6.fib6_local_tbl);
-#endif
-	inetpeer_invalidate_tree(&net->ipv6.fib6_main_tbl->tb6_peers);
-	kfree(net->ipv6.fib6_main_tbl);
+	for (i = 0; i < FIB_TABLE_HASHSZ; i++) {
+		struct hlist_head *head = &net->ipv6.fib_table_hash[i];
+		struct hlist_node *tmp;
+		struct fib6_table *tb;
+
+		hlist_for_each_entry_safe(tb, tmp, head, tb6_hlist) {
+			hlist_del(&tb->tb6_hlist);
+			fib6_free_table(tb);
+		}
+	}
+
 	kfree(net->ipv6.fib_table_hash);
 	kfree(net->ipv6.rt6_stats);
 	fib6_notifier_exit(net);