> The following 3 locks would race against each other, causing the > deadlock situation in the Syzbot bug report: > > - j1939_socks_lock > - active_session_list_lock > - sk_session_queue_lock > > A reasonable fix is to change j1939_socks_lock to an rwlock, since in > the rare situations where a write lock is required for the linked list > that j1939_socks_lock is protecting, the code does not attempt to > acquire any more locks. This would break the circular lock dependency, > where, for example, the current thread already locks j1939_socks_lock > and attempts to acquire sk_session_queue_lock, and at the same time, > another thread attempts to acquire j1939_socks_lock while holding > sk_session_queue_lock. > > NOTE: This patch along does not fix the unregister_netdevice bug > reported by Syzbot; instead, it solves a deadlock situation to prepare > for one or more further patches to actually fix the Syzbot bug, which > appears to be a reference counting problem within the j1939 codebase. > > #syz test: This crash does not have a reproducer. I cannot test it. > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master > > Signed-off-by: Ziqi Zhao <astrajoan@xxxxxxxxx> > --- > net/can/j1939/j1939-priv.h | 2 +- > net/can/j1939/main.c | 2 +- > net/can/j1939/socket.c | 25 +++++++++++++------------ > 3 files changed, 15 insertions(+), 14 deletions(-) > > diff --git a/net/can/j1939/j1939-priv.h b/net/can/j1939/j1939-priv.h > index 16af1a7f80f6..74f15592d170 100644 > --- a/net/can/j1939/j1939-priv.h > +++ b/net/can/j1939/j1939-priv.h > @@ -86,7 +86,7 @@ struct j1939_priv { > unsigned int tp_max_packet_size; > > /* lock for j1939_socks list */ > - spinlock_t j1939_socks_lock; > + rwlock_t j1939_socks_lock; > struct list_head j1939_socks; > > struct kref rx_kref; > diff --git a/net/can/j1939/main.c b/net/can/j1939/main.c > index ecff1c947d68..a6fb89fa6278 100644 > --- a/net/can/j1939/main.c > +++ b/net/can/j1939/main.c > @@ -274,7 +274,7 @@ struct j1939_priv *j1939_netdev_start(struct net_device *ndev) > return ERR_PTR(-ENOMEM); > > j1939_tp_init(priv); > - spin_lock_init(&priv->j1939_socks_lock); > + rwlock_init(&priv->j1939_socks_lock); > INIT_LIST_HEAD(&priv->j1939_socks); > > mutex_lock(&j1939_netdev_lock); > diff --git a/net/can/j1939/socket.c b/net/can/j1939/socket.c > index feaec4ad6d16..a8b981dc2065 100644 > --- a/net/can/j1939/socket.c > +++ b/net/can/j1939/socket.c > @@ -80,16 +80,16 @@ static void j1939_jsk_add(struct j1939_priv *priv, struct j1939_sock *jsk) > jsk->state |= J1939_SOCK_BOUND; > j1939_priv_get(priv); > > - spin_lock_bh(&priv->j1939_socks_lock); > + write_lock_bh(&priv->j1939_socks_lock); > list_add_tail(&jsk->list, &priv->j1939_socks); > - spin_unlock_bh(&priv->j1939_socks_lock); > + write_unlock_bh(&priv->j1939_socks_lock); > } > > static void j1939_jsk_del(struct j1939_priv *priv, struct j1939_sock *jsk) > { > - spin_lock_bh(&priv->j1939_socks_lock); > + write_lock_bh(&priv->j1939_socks_lock); > list_del_init(&jsk->list); > - spin_unlock_bh(&priv->j1939_socks_lock); > + write_unlock_bh(&priv->j1939_socks_lock); > > j1939_priv_put(priv); > jsk->state &= ~J1939_SOCK_BOUND; > @@ -329,13 +329,13 @@ bool j1939_sk_recv_match(struct j1939_priv *priv, struct j1939_sk_buff_cb *skcb) > struct j1939_sock *jsk; > bool match = false; > > - spin_lock_bh(&priv->j1939_socks_lock); > + read_lock_bh(&priv->j1939_socks_lock); > list_for_each_entry(jsk, &priv->j1939_socks, list) { > match = j1939_sk_recv_match_one(jsk, skcb); > if (match) > break; > } > - spin_unlock_bh(&priv->j1939_socks_lock); > + read_unlock_bh(&priv->j1939_socks_lock); > > return match; > } > @@ -344,11 +344,11 @@ void j1939_sk_recv(struct j1939_priv *priv, struct sk_buff *skb) > { > struct j1939_sock *jsk; > > - spin_lock_bh(&priv->j1939_socks_lock); > + read_lock_bh(&priv->j1939_socks_lock); > list_for_each_entry(jsk, &priv->j1939_socks, list) { > j1939_sk_recv_one(jsk, skb); > } > - spin_unlock_bh(&priv->j1939_socks_lock); > + read_unlock_bh(&priv->j1939_socks_lock); > } > > static void j1939_sk_sock_destruct(struct sock *sk) > @@ -484,6 +484,7 @@ static int j1939_sk_bind(struct socket *sock, struct sockaddr *uaddr, int len) > > priv = j1939_netdev_start(ndev); > dev_put(ndev); > + > if (IS_ERR(priv)) { > ret = PTR_ERR(priv); > goto out_release_sock; > @@ -1078,12 +1079,12 @@ void j1939_sk_errqueue(struct j1939_session *session, > } > > /* spread RX notifications to all sockets subscribed to this session */ > - spin_lock_bh(&priv->j1939_socks_lock); > + read_lock_bh(&priv->j1939_socks_lock); > list_for_each_entry(jsk, &priv->j1939_socks, list) { > if (j1939_sk_recv_match_one(jsk, &session->skcb)) > __j1939_sk_errqueue(session, &jsk->sk, type); > } > - spin_unlock_bh(&priv->j1939_socks_lock); > + read_unlock_bh(&priv->j1939_socks_lock); > }; > > void j1939_sk_send_loop_abort(struct sock *sk, int err) > @@ -1271,7 +1272,7 @@ void j1939_sk_netdev_event_netdown(struct j1939_priv *priv) > struct j1939_sock *jsk; > int error_code = ENETDOWN; > > - spin_lock_bh(&priv->j1939_socks_lock); > + read_lock_bh(&priv->j1939_socks_lock); > list_for_each_entry(jsk, &priv->j1939_socks, list) { > jsk->sk.sk_err = error_code; > if (!sock_flag(&jsk->sk, SOCK_DEAD)) > @@ -1279,7 +1280,7 @@ void j1939_sk_netdev_event_netdown(struct j1939_priv *priv) > > j1939_sk_queue_drop_all(priv, jsk, error_code); > } > - spin_unlock_bh(&priv->j1939_socks_lock); > + read_unlock_bh(&priv->j1939_socks_lock); > } > > static int j1939_sk_no_ioctlcmd(struct socket *sock, unsigned int cmd, > -- > 2.34.1 >
