netfilter: nf_tables: Fix potential data-race in __nft_expr_type_get()

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>

diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c
index d89d779467197a0846406e0b0ce6938e8a3d404d..53b8c00863ad214ad89aa8e85531dff98cc455f3 100644 (file)
--- 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