netfilter: helper: Add the rcu lock when call __nf_conntrack_helper_find

When invoke __nf_conntrack_helper_find, it needs the rcu lock to
protect the helper module which would not be unloaded.

Now there are two caller nf_conntrack_helper_try_module_get and
ctnetlink_create_expect which don't hold rcu lock. And the other
callers left like ctnetlink_change_helper, ctnetlink_create_conntrack,
and ctnetlink_glue_attach_expect, they already hold the rcu lock
or spin_lock_bh.

Remove the rcu lock in functions nf_ct_helper_expectfn_find_by_name
and nf_ct_helper_expectfn_find_by_symbol. Because they return one pointer
which needs rcu lock, so their caller should hold the rcu lock, not in
these two functions.

Signed-off-by: Gao Feng <fgao@ikuai8.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_conntrack_helper.c

@@ -158,16 +158,25 @@ nf_conntrack_helper_try_module_get(const char *name, u16 l3num, u8 protonum)
 {
 	struct nf_conntrack_helper *h;
 
+	rcu_read_lock();
+
 	h = __nf_conntrack_helper_find(name, l3num, protonum);
 #ifdef CONFIG_MODULES
 	if (h == NULL) {
-		if (request_module("nfct-helper-%s", name) == 0)
+		rcu_read_unlock();
+		if (request_module("nfct-helper-%s", name) == 0) {
+			rcu_read_lock();
 			h = __nf_conntrack_helper_find(name, l3num, protonum);
+		} else {
+			return h;
+		}
 	}
 #endif
 	if (h != NULL && !try_module_get(h->me))
 		h = NULL;
 
+	rcu_read_unlock();
+
 	return h;
 }
 EXPORT_SYMBOL_GPL(nf_conntrack_helper_try_module_get);
@@ -311,38 +320,36 @@ void nf_ct_helper_expectfn_unregister(struct nf_ct_helper_expectfn *n)
 }
 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_unregister);
 
+/* Caller should hold the rcu lock */
 struct nf_ct_helper_expectfn *
 nf_ct_helper_expectfn_find_by_name(const char *name)
 {
 	struct nf_ct_helper_expectfn *cur;
 	bool found = false;
 
-	rcu_read_lock();
 	list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
 		if (!strcmp(cur->name, name)) {
 			found = true;
 			break;
 		}
 	}
-	rcu_read_unlock();
 	return found ? cur : NULL;
 }
 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_name);
 
+/* Caller should hold the rcu lock */
 struct nf_ct_helper_expectfn *
 nf_ct_helper_expectfn_find_by_symbol(const void *symbol)
 {
 	struct nf_ct_helper_expectfn *cur;
 	bool found = false;
 
-	rcu_read_lock();
 	list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
 		if (cur->expectfn == symbol) {
 			found = true;
 			break;
 		}
 	}
-	rcu_read_unlock();
 	return found ? cur : NULL;
 }
 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_symbol);

net/netfilter/nf_conntrack_netlink.c

@@ -3133,23 +3133,27 @@ ctnetlink_create_expect(struct net *net,
 		return -ENOENT;
 	ct = nf_ct_tuplehash_to_ctrack(h);
 
+	rcu_read_lock();
 	if (cda[CTA_EXPECT_HELP_NAME]) {
 		const char *helpname = nla_data(cda[CTA_EXPECT_HELP_NAME]);
 
 		helper = __nf_conntrack_helper_find(helpname, u3,
 						    nf_ct_protonum(ct));
 		if (helper == NULL) {
+			rcu_read_unlock();
 #ifdef CONFIG_MODULES
 			if (request_module("nfct-helper-%s", helpname) < 0) {
 				err = -EOPNOTSUPP;
 				goto err_ct;
 			}
+			rcu_read_lock();
 			helper = __nf_conntrack_helper_find(helpname, u3,
 							    nf_ct_protonum(ct));
 			if (helper) {
 				err = -EAGAIN;
-				goto err_ct;
+				goto err_rcu;
 			}
+			rcu_read_unlock();
 #endif
 			err = -EOPNOTSUPP;
 			goto err_ct;
@@ -3159,11 +3163,13 @@ ctnetlink_create_expect(struct net *net,
 	exp = ctnetlink_alloc_expect(cda, ct, helper, &tuple, &mask);
 	if (IS_ERR(exp)) {
 		err = PTR_ERR(exp);
-		goto err_ct;
+		goto err_rcu;
 	}
 
 	err = nf_ct_expect_related_report(exp, portid, report);
 	nf_ct_expect_put(exp);
+err_rcu:
+	rcu_read_unlock();
 err_ct:
 	nf_ct_put(ct);
 	return err;