mptcp: pm: use _rcu variant under rcu_read_lock

In mptcp_pm_create_subflow_or_signal_addr(), rcu_read_(un)lock() are
used as expected to iterate over the list of local addresses, but
list_for_each_entry() was used instead of list_for_each_entry_rcu() in
__lookup_addr() (and lookup_id_by_addr() before). It is important to use
this variant which adds the required READ_ONCE() (and diagnostic checks
if enabled).

Because __lookup_addr() is also used in mptcp_pm_nl_set_flags() where it
is called under the pernet->lock because the returned entry might be
modified, the _rcu variant cannot be used in all cases. It is then
required to create a new helper. Note that this new helper can be reused
later to reduce some duplicated code elsewhere in this file.

Fixes: 86e39e0 ("mptcp: keep track of local endpoint still available for each msk")
Signed-off-by: Matthieu Baerts (NGI0) <[email protected]>

net/mptcp/pm_netlink.c

@@ -531,6 +531,18 @@ __lookup_addr(struct pm_nl_pernet *pernet, const struct mptcp_addr_info *info)
 	return NULL;
 }
 
+static struct mptcp_pm_addr_entry *
+__lookup_addr_rcu(struct pm_nl_pernet *pernet, const struct mptcp_addr_info *info)
+{
+	struct mptcp_pm_addr_entry *entry;
+
+	list_for_each_entry_rcu(entry, &pernet->local_addr_list, list) {
+		if (mptcp_addresses_equal(&entry->addr, info, entry->addr.port))
+			return entry;
+	}
+	return NULL;
+}
+
 static void mptcp_pm_create_subflow_or_signal_addr(struct mptcp_sock *msk)
 {
 	struct sock *sk = (struct sock *)msk;
@@ -556,7 +568,7 @@ static void mptcp_pm_create_subflow_or_signal_addr(struct mptcp_sock *msk)
 
 		mptcp_local_address((struct sock_common *)msk->first, &mpc_addr);
 		rcu_read_lock();
-		entry = __lookup_addr(pernet, &mpc_addr);
+		entry = __lookup_addr_rcu(pernet, &mpc_addr);
 		if (entry) {
 			__clear_bit(entry->addr.id, msk->pm.id_avail_bitmap);
 			msk->mpc_endpoint_id = entry->addr.id;