[PATCH net 04/19] can: j1939: fix lockless local-destination check
From: Marc Kleine-Budde <mkl@pengutronix.de>
Date: 2026-07-16 15:56:41
Also in:
linux-can
Subsystem:
can network layer, can-j1939 network layer, the rest · Maintainers:
Oliver Hartkopp, Marc Kleine-Budde, Robin van der Gracht, Oleksij Rempel, Linus Torvalds
From: Shuhao Fu <redacted>
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 <redacted>
Tested-by: Oleksij Rempel <o.rempel@pengutronix.de>
Acked-by: Oleksij Rempel <o.rempel@pengutronix.de>
Link: https://patch.msgid.link/20260419140614.GA4041240@chcpu16
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
---
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 df93d57907da..8a31cb23bc76 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