[PATCH v1 net-next 03/10] ipv4: fib: Protect fib_new_table() with spinlock.

[Kuniyuki Iwashima <kuniyu@google.com>]

fib_newrule() will drop RTNL except for the first IPv4 rule.

Then, fib4_rule_configure() could call fib_empty_table() and create
a new IPv4 fib_table without RTNL.

Currently, net->ipv4.fib_table_hash[] is only protected by RTNL.

As a prep, let's protect net->ipv4.fib_table_hash[] with a dedicated
spinlock.

Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
---
 include/net/netns/ipv4.h |  1 +
 net/ipv4/fib_frontend.c  | 25 +++++++++++++++++++++----
 2 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/include/net/netns/ipv4.h b/include/net/netns/ipv4.h
index 6e27c56514df..59506320558a 100644
--- a/include/net/netns/ipv4.h
+++ b/include/net/netns/ipv4.h
@@ -127,6 +127,7 @@ struct netns_ipv4 {
 	atomic_t		fib_num_tclassid_users;
 #endif
 	struct hlist_head	*fib_table_hash;
+	spinlock_t		fib_table_hash_lock;
 	struct sock		*fibnl;
 	struct hlist_head	*fib_info_hash;
 	unsigned int		fib_info_hash_bits;
diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_frontend.c
index 42212970d735..336d70649eb9 100644
--- a/net/ipv4/fib_frontend.c
+++ b/net/ipv4/fib_frontend.c
@@ -76,7 +76,7 @@ static int __net_init fib4_rules_init(struct net *net)
 
 struct fib_table *fib_new_table(struct net *net, u32 id)
 {
-	struct fib_table *tb, *alias = NULL;
+	struct fib_table *tb, *new_tb, *alias = NULL;
 	unsigned int h;
 
 	if (id == 0)
@@ -85,14 +85,27 @@ struct fib_table *fib_new_table(struct net *net, u32 id)
 	if (tb)
 		return tb;
 
+	if (!check_net(net))
+		return NULL;
+
 	if (id == RT_TABLE_LOCAL && !net->ipv4.fib_has_custom_rules)
 		alias = fib_new_table(net, RT_TABLE_MAIN);
 
-	if (check_net(net))
-		tb = fib_trie_table(id, alias);
-	if (!tb)
+	new_tb = fib_trie_table(id, alias);
+	if (!new_tb)
 		return NULL;
 
+	spin_lock(&net->ipv4.fib_table_hash_lock);
+
+	tb = fib_get_table(net, id);
+	if (tb) {
+		spin_unlock(&net->ipv4.fib_table_hash_lock);
+		fib_free_table(new_tb);
+		return tb;
+	}
+
+	tb = new_tb;
+
 	switch (id) {
 	case RT_TABLE_MAIN:
 		rcu_assign_pointer(net->ipv4.fib_main, tb);
@@ -106,6 +119,9 @@ struct fib_table *fib_new_table(struct net *net, u32 id)
 
 	h = id & (FIB_TABLE_HASHSZ - 1);
 	hlist_add_head_rcu(&tb->tb_hlist, &net->ipv4.fib_table_hash[h]);
+
+	spin_unlock(&net->ipv4.fib_table_hash_lock);
+
 	return tb;
 }
 EXPORT_SYMBOL_GPL(fib_new_table);
@@ -1565,6 +1581,7 @@ static int __net_init ip_fib_net_init(struct net *net)
 	net->ipv4.sysctl_fib_multipath_hash_fields =
 		FIB_MULTIPATH_HASH_FIELD_DEFAULT_MASK;
 #endif
+	spin_lock_init(&net->ipv4.fib_table_hash_lock);
 
 	/* Avoid false sharing : Use at least a full cache line */
 	size = max_t(size_t, size, L1_CACHE_BYTES);
-- 
2.55.0.rc0.799.gd6f94ed593-goog