[PATCH net 1/7] netfilter: nf_tables: Fix potential data-race in __nft_expr_type_get()

[Pablo Neira Ayuso <pablo@netfilter.org>]

From: Ziyang Xuan <william.xuanziyang@huawei.com>

nft_unregister_expr() can concurrent with __nft_expr_type_get(),
and there is not any protection when iterate over nf_tables_expressions
list in __nft_expr_type_get(). Therefore, there is potential data-race
of nf_tables_expressions list entry.

Use list_for_each_entry_rcu() to iterate over nf_tables_expressions
list in __nft_expr_type_get(), and use rcu_read_lock() in the caller
nft_expr_type_get() to protect the entire type query process.

Fixes: ef1f7df9170d ("netfilter: nf_tables: expression ops overloading")
Signed-off-by: Ziyang Xuan <william.xuanziyang@huawei.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---
 net/netfilter/nf_tables_api.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c
index d89d77946719..53b8c00863ad 100644
--- a/net/netfilter/nf_tables_api.c
+++ b/net/netfilter/nf_tables_api.c
@@ -3060,7 +3060,7 @@ static const struct nft_expr_type *__nft_expr_type_get(u8 family,
 {
 	const struct nft_expr_type *type, *candidate = NULL;
 
-	list_for_each_entry(type, &nf_tables_expressions, list) {
+	list_for_each_entry_rcu(type, &nf_tables_expressions, list) {
 		if (!nla_strcmp(nla, type->name)) {
 			if (!type->family && !candidate)
 				candidate = type;
@@ -3092,9 +3092,13 @@ static const struct nft_expr_type *nft_expr_type_get(struct net *net,
 	if (nla == NULL)
 		return ERR_PTR(-EINVAL);
 
+	rcu_read_lock();
 	type = __nft_expr_type_get(family, nla);
-	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
-- 
2.30.2