fib_trie: Make fib_table rcu safe

The fib_table was wrapped in several places with an
rcu_read_lock/rcu_read_unlock however after looking over the code I found
several spots where the tables were being accessed as just standard
pointers without any protections.  This change fixes that so that all of
the proper protections are in place when accessing the table to take RCU
replacement or removal of the table into account.

Signed-off-by: Alexander Duyck <alexander.h.duyck@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 37 insertions, 15 deletions

diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_frontend.c
index 57be71dd6a9e..220c4b4af4cf 100644
--- a/net/ipv4/fib_frontend.c
+++ b/net/ipv4/fib_frontend.c
@@ -89,17 +89,14 @@ struct fib_table *fib_new_table(struct net *net, u32 id)
 
 	switch (id) {
 	case RT_TABLE_LOCAL:
-		net->ipv4.fib_local = tb;
+		rcu_assign_pointer(net->ipv4.fib_local, tb);
 		break;
-
 	case RT_TABLE_MAIN:
-		net->ipv4.fib_main = tb;
+		rcu_assign_pointer(net->ipv4.fib_main, tb);
 		break;
-
 	case RT_TABLE_DEFAULT:
-		net->ipv4.fib_default = tb;
+		rcu_assign_pointer(net->ipv4.fib_default, tb);
 		break;
-
 	default:
 		break;
 	}
@@ -132,13 +129,14 @@ struct fib_table *fib_get_table(struct net *net, u32 id)
 static void fib_flush(struct net *net)
 {
 	int flushed = 0;
-	struct fib_table *tb;
-	struct hlist_head *head;
 	unsigned int h;
 
 	for (h = 0; h < FIB_TABLE_HASHSZ; h++) {
-		head = &net->ipv4.fib_table_hash[h];
-		hlist_for_each_entry(tb, head, tb_hlist)
+		struct hlist_head *head = &net->ipv4.fib_table_hash[h];
+		struct hlist_node *tmp;
+		struct fib_table *tb;
+
+		hlist_for_each_entry_safe(tb, tmp, head, tb_hlist)
 			flushed += fib_table_flush(tb);
 	}
 
@@ -665,10 +663,12 @@ static int inet_dump_fib(struct sk_buff *skb, struct netlink_callback *cb)
 	s_h = cb->args[0];
 	s_e = cb->args[1];
 
+	rcu_read_lock();
+
 	for (h = s_h; h < FIB_TABLE_HASHSZ; h++, s_e = 0) {
 		e = 0;
 		head = &net->ipv4.fib_table_hash[h];
-		hlist_for_each_entry(tb, head, tb_hlist) {
+		hlist_for_each_entry_rcu(tb, head, tb_hlist) {
 			if (e < s_e)
 				goto next;
 			if (dumped)
@@ -682,6 +682,8 @@ next:
 		}
 	}
 out:
+	rcu_read_unlock();
+
 	cb->args[1] = e;
 	cb->args[0] = h;
 
@@ -1117,14 +1119,34 @@ static void ip_fib_net_exit(struct net *net)
 
 	rtnl_lock();
 	for (i = 0; i < FIB_TABLE_HASHSZ; i++) {
-		struct fib_table *tb;
-		struct hlist_head *head;
+		struct hlist_head *head = &net->ipv4.fib_table_hash[i];
 		struct hlist_node *tmp;
+		struct fib_table *tb;
+
+		/* this is done in two passes as flushing the table could
+		 * cause it to be reallocated in order to accommodate new
+		 * tnodes at the root as the table shrinks.
+		 */
+		hlist_for_each_entry_safe(tb, tmp, head, tb_hlist)
+			fib_table_flush(tb);
 
-		head = &net->ipv4.fib_table_hash[i];
 		hlist_for_each_entry_safe(tb, tmp, head, tb_hlist) {
+#ifdef CONFIG_IP_MULTIPLE_TABLES
+			switch (tb->tb_id) {
+			case RT_TABLE_LOCAL:
+				RCU_INIT_POINTER(net->ipv4.fib_local, NULL);
+				break;
+			case RT_TABLE_MAIN:
+				RCU_INIT_POINTER(net->ipv4.fib_main, NULL);
+				break;
+			case RT_TABLE_DEFAULT:
+				RCU_INIT_POINTER(net->ipv4.fib_default, NULL);
+				break;
+			default:
+				break;
+			}
+#endif
 			hlist_del(&tb->tb_hlist);
-			fib_table_flush(tb);
 			fib_free_table(tb);
 		}
 	}