l2tp: do not use sock_hold() in pppol2tp_session_get_sock()

pppol2tp_session_get_sock() is using RCU, it must be ready
for sk_refcnt being zero.

Commit ee40fb2e1eb5 ("l2tp: protect sock pointer of
struct pppol2tp_session with RCU") was correct because it
had a call_rcu(..., pppol2tp_put_sk) which was later removed in blamed commit.

pppol2tp_recv() can use pppol2tp_session_get_sock() as well.

Fixes: c5cbaef992d6 ("l2tp: refactor ppp socket/session relationship")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: James Chapman <jchapman@katalix.com>
Reviewed-by: Guillaume Nault <gnault@redhat.com>
Link: https://patch.msgid.link/20250826134435.1683435-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/l2tp/l2tp_ppp.c b/net/l2tp/l2tp_ppp.c
index fc5c2fd8f34c7ec23e6f5ab978ea96c9f48ac81d..5e12e7ce17d8a7cf4afc2486f1c3c42f98feddf1 100644 (file)
--- a/net/l2tp/l2tp_ppp.c
+++ b/net/l2tp/l2tp_ppp.c
@@ -129,22 +129,12 @@ static const struct ppp_channel_ops pppol2tp_chan_ops = {
 
 static const struct proto_ops pppol2tp_ops;
 
-/* Retrieves the pppol2tp socket associated to a session.
- * A reference is held on the returned socket, so this function must be paired
- * with sock_put().
- */
+/* Retrieves the pppol2tp socket associated to a session. */
 static struct sock *pppol2tp_session_get_sock(struct l2tp_session *session)
 {
        struct pppol2tp_session *ps = l2tp_session_priv(session);
-       struct sock *sk;
-
-       rcu_read_lock();
-       sk = rcu_dereference(ps->sk);
-       if (sk)
-               sock_hold(sk);
-       rcu_read_unlock();
 
-       return sk;
+       return rcu_dereference(ps->sk);
 }
 
 /* Helpers to obtain tunnel/session contexts from sockets.
@@ -206,14 +196,13 @@ end:
 
 static void pppol2tp_recv(struct l2tp_session *session, struct sk_buff *skb, int data_len)
 {
-       struct pppol2tp_session *ps = l2tp_session_priv(session);
-       struct sock *sk = NULL;
+       struct sock *sk;
 
        /* If the socket is bound, send it in to PPP's input queue. Otherwise
         * queue it on the session socket.
         */
        rcu_read_lock();
-       sk = rcu_dereference(ps->sk);
+       sk = pppol2tp_session_get_sock(session);
        if (!sk)
                goto no_sock;
 
@@ -510,13 +499,14 @@ static void pppol2tp_show(struct seq_file *m, void *arg)
        struct l2tp_session *session = arg;
        struct sock *sk;
 
+       rcu_read_lock();
        sk = pppol2tp_session_get_sock(session);
        if (sk) {
                struct pppox_sock *po = pppox_sk(sk);
 
                seq_printf(m, "   interface %s\n", ppp_dev_name(&po->chan));
-               sock_put(sk);
        }
+       rcu_read_unlock();
 }
 
 static void pppol2tp_session_init(struct l2tp_session *session)
@@ -1530,6 +1520,7 @@ static void pppol2tp_seq_session_show(struct seq_file *m, void *v)
                port = ntohs(inet->inet_sport);
        }
 
+       rcu_read_lock();
        sk = pppol2tp_session_get_sock(session);
        if (sk) {
                state = sk->sk_state;
@@ -1565,8 +1556,8 @@ static void pppol2tp_seq_session_show(struct seq_file *m, void *v)
                struct pppox_sock *po = pppox_sk(sk);
 
                seq_printf(m, "   interface %s\n", ppp_dev_name(&po->chan));
-               sock_put(sk);
        }
+       rcu_read_unlock();
 }
 
 static int pppol2tp_seq_show(struct seq_file *m, void *v)