From: Shuhao Fu j1939_priv.ents[].nusers is documented as protected by priv->lock, and its updates already happen under that lock. j1939_can_recv() also reads it under read_lock_bh(). However, j1939_session_skb_queue() and j1939_tp_send() still read priv->ents[da].nusers without taking the lock. Those transport-side checks decide whether to set J1939_ECU_LOCAL_DST, so they can race with j1939_local_ecu_get() and j1939_local_ecu_put() while userspace is binding or releasing sockets concurrently with TP traffic. This can misclassify TP/ETP sessions as local or remote and take the wrong transport path. Fix both transport paths by routing the destination-locality check through a helper that reads ents[].nusers under read_lock_bh(&priv->lock). Fixes: 9d71dd0c7009 ("can: add support of SAE J1939 protocol") Signed-off-by: Shuhao Fu Tested-by: Oleksij Rempel Acked-by: Oleksij Rempel Link: https://patch.msgid.link/20260419140614.GA4041240@chcpu16 Signed-off-by: Marc Kleine-Budde --- net/can/j1939/transport.c | 18 ++++++++++++++---- 1 file changed, 14 insertions(+), 4 deletions(-) diff --git a/net/can/j1939/transport.c b/net/can/j1939/transport.c index 7ad56b5f17b9..25d96976d9d0 100644 --- a/net/can/j1939/transport.c +++ b/net/can/j1939/transport.c @@ -351,6 +351,18 @@ static void j1939_session_skb_drop_old(struct j1939_session *session) } } +static bool j1939_address_is_local(struct j1939_priv *priv, u8 addr) +{ + bool local = false; + + read_lock_bh(&priv->lock); + if (j1939_address_is_unicast(addr) && priv->ents[addr].nusers) + local = true; + read_unlock_bh(&priv->lock); + + return local; +} + void j1939_session_skb_queue(struct j1939_session *session, struct sk_buff *skb) { @@ -359,8 +371,7 @@ void j1939_session_skb_queue(struct j1939_session *session, j1939_ac_fixup(priv, skb); - if (j1939_address_is_unicast(skcb->addr.da) && - priv->ents[skcb->addr.da].nusers) + if (j1939_address_is_local(priv, skcb->addr.da)) skcb->flags |= J1939_ECU_LOCAL_DST; skcb->flags |= J1939_ECU_LOCAL_SRC; @@ -2038,8 +2049,7 @@ struct j1939_session *j1939_tp_send(struct j1939_priv *priv, return ERR_PTR(ret); /* fix DST flags, it may be used there soon */ - if (j1939_address_is_unicast(skcb->addr.da) && - priv->ents[skcb->addr.da].nusers) + if (j1939_address_is_local(priv, skcb->addr.da)) skcb->flags |= J1939_ECU_LOCAL_DST; /* src is always local, I'm sending ... */ -- 2.53.0