[PATCH 4.19 122/175] netfilter: nf_tables: Fix potential data-race in __nft_flowtable_type_get()

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4.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ziyang Xuan <william.xuanziyang@xxxxxxxxxx>

commit 24225011d81b471acc0e1e315b7d9905459a6304 upstream.

nft_unregister_flowtable_type() within nf_flow_inet_module_exit() can
concurrent with __nft_flowtable_type_get() within nf_tables_newflowtable().
And thhere is not any protection when iterate over nf_tables_flowtables
list in __nft_flowtable_type_get(). Therefore, there is pertential
data-race of nf_tables_flowtables list entry.

Use list_for_each_entry_rcu() to iterate over nf_tables_flowtables list
in __nft_flowtable_type_get(), and use rcu_read_lock() in the caller
nft_flowtable_type_get() to protect the entire type query process.

Fixes: 3b49e2e94e6e ("netfilter: nf_tables: add flow table netlink frontend")
Signed-off-by: Ziyang Xuan <william.xuanziyang@xxxxxxxxxx>
Signed-off-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 net/netfilter/nf_tables_api.c |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

--- a/net/netfilter/nf_tables_api.c
+++ b/net/netfilter/nf_tables_api.c
@@ -5721,11 +5721,12 @@ static int nf_tables_flowtable_parse_hoo
 	return err;
 }
 
+/* call under rcu_read_lock */
 static const struct nf_flowtable_type *__nft_flowtable_type_get(u8 family)
 {
 	const struct nf_flowtable_type *type;
 
-	list_for_each_entry(type, &nf_tables_flowtables, list) {
+	list_for_each_entry_rcu(type, &nf_tables_flowtables, list) {
 		if (family == type->family)
 			return type;
 	}
@@ -5737,9 +5738,13 @@ nft_flowtable_type_get(struct net *net,
 {
 	const struct nf_flowtable_type *type;
 
+	rcu_read_lock();
 	type = __nft_flowtable_type_get(family);
-	if (type != NULL && try_module_get(type->owner))
+	if (type != NULL && try_module_get(type->owner)) {
+		rcu_read_unlock();
 		return type;
+	}
+	rcu_read_unlock();
 
 	lockdep_nfnl_nft_mutex_not_held();
 #ifdef CONFIG_MODULES






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