[PATCH net 14/19] can: bcm: fix stale rx/tx ops after device removal

[Marc Kleine-Budde <mkl@pengutronix.de>]

From: Oliver Hartkopp <socketcan@hartkopp.net>

RX: an RX_SETUP update(!) for an existing op skipped can_rx_register()
unconditionally, even when a concurrent NETDEV_UNREGISTER had already
torn down its registration (op->rx_reg_dev == NULL). This silently
did not re-enable frame delivery for that updated filter. bcm_rx_setup()
now re-registers in that case, while leaving rx_ops with ifindex = 0
(all CAN devices) which never carry a tracked rx_reg_dev registered as-is.

TX: bcm_notify() only handled bo->rx_ops on NETDEV_UNREGISTER, leaving
tx_ops with an active cyclic transmission re-arming its hrtimer
indefinitely to execute bcm_tx_timeout_handler(). Cancelling the hrtimer
prevents the runaway timer and any injection into a later reused ifindex,
since nothing else calls bcm_can_tx() for the op until an explicit
TX_SETUP update re-arms it.

Unlike bcm_rx_unreg(), which clears the tracked rx_reg_dev for rx_ops,
the ifindex is intentionally left unchanged for tx_ops. bcm_tx_setup()
always rejects ifindex 0, so clearing it would strand the op: neither a
later TX_SETUP (bcm_find_op()) nor TX_DELETE (bcm_delete_tx_op()) could
ever find it again, since both require an exact ifindex match.

Reported-by: sashiko-bot@kernel.org
Closes: https://lore.kernel.org/linux-can/20260708094536.DDF821F00A3A@smtp.kernel.org/
Closes: https://lore.kernel.org/linux-can/20260708154039.347ED1F000E9@smtp.kernel.org/
Fixes: ffd980f976e7 ("[CAN]: Add broadcast manager (bcm) protocol")
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Link: https://patch.msgid.link/20260714-bcm_fixes-v15-9-562f7e3e42da@hartkopp.net
Cc: stable@kernel.org
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
---
 net/can/bcm.c | 54 +++++++++++++++++++++++++++++++++++++++++----------
 1 file changed, 44 insertions(+), 10 deletions(-)

diff --git a/net/can/bcm.c b/net/can/bcm.c
index 25842061800b..a53dba6ab8b8 100644
--- a/net/can/bcm.c
+++ b/net/can/bcm.c
@@ -1287,6 +1287,7 @@ static int bcm_rx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
 	struct bcm_sock *bo = bcm_sk(sk);
 	struct bcm_op *op;
 	int do_rx_register;
+	int new_op = 0;
 	int err = 0;
 
 	if ((msg_head->flags & RX_FILTER_ID) || (!(msg_head->nframes))) {
@@ -1371,8 +1372,15 @@ static int bcm_rx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
 		/* free temporary frames / kfree(NULL) is safe */
 		kfree(new_frames);
 
-		/* Only an update -> do not call can_rx_register() */
-		do_rx_register = 0;
+		/* Don't register a new CAN filter for the rx_op update unless
+		 * a concurrent NETDEV_UNREGISTER notifier already tore down
+		 * the previous registration. In this case the receiver needs
+		 * to be re-registered here so that this update doesn't
+		 * silently stop delivering frames for the given ifindex.
+		 * Ops with ifindex = 0 (all CAN interfaces) never carry a
+		 * tracked rx_reg_dev and stay registered as-is.
+		 */
+		do_rx_register = (ifindex && !op->rx_reg_dev) ? 1 : 0;
 
 	} else {
 		/* insert new BCM operation for the given can_id */
@@ -1439,6 +1447,7 @@ static int bcm_rx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
 
 		/* call can_rx_register() */
 		do_rx_register = 1;
+		new_op = 1;
 
 	} /* if ((op = bcm_find_op(&bo->rx_ops, msg_head->can_id, ifindex))) */
 
@@ -1452,7 +1461,7 @@ static int bcm_rx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
 		if (op->flags & SETTIMER) {
 
 			/* set timers (locked) for newly created op */
-			if (do_rx_register) {
+			if (new_op) {
 				spin_lock_bh(&op->bcm_rx_update_lock);
 				op->ival1 = msg_head->ival1;
 				op->ival2 = msg_head->ival2;
@@ -1482,7 +1491,10 @@ static int bcm_rx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
 				      HRTIMER_MODE_REL_SOFT);
 	}
 
-	/* now we can register for can_ids, if we added a new bcm_op */
+	/* now we can register for can_ids, if we added a new bcm_op
+	 * or need to re-register after a NETDEV_UNREGISTER tore down
+	 * the previous registration of an existing op
+	 */
 	if (do_rx_register) {
 		if (ifindex) {
 			struct net_device *dev;
@@ -1514,18 +1526,32 @@ static int bcm_rx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
 				err = -ENODEV;
 			}
 
-		} else
+		} else {
 			err = can_rx_register(sock_net(sk), NULL, op->can_id,
 					      REGMASK(op->can_id),
 					      bcm_rx_handler, op, "bcm", sk);
+		}
+
 		if (err) {
-			/* this bcm rx op is broken -> remove it */
-			bcm_remove_op(op);
+			/* newly created bcm rx op is broken -> remove it */
+			if (new_op) {
+				bcm_remove_op(op);
+				return err;
+			}
+
+			/* an existing op just stays unregistered.
+			 * Cancel op->timer and (defensively) op->thrtimer.
+			 * Other settings can't be reached until the next
+			 * successful RX_SETUP.
+			 */
+			hrtimer_cancel(&op->timer);
+			hrtimer_cancel(&op->thrtimer);
 			return err;
 		}
 
-		/* add this bcm_op to the list of the rx_ops */
-		list_add_rcu(&op->list, &bo->rx_ops);
+		/* add a new bcm_op to the list of the rx_ops */
+		if (new_op)
+			list_add_rcu(&op->list, &bo->rx_ops);
 	}
 
 	return msg_head->nframes * op->cfsiz + MHSIZ;
@@ -1745,11 +1771,19 @@ static void bcm_notify(struct bcm_sock *bo, unsigned long msg,
 	case NETDEV_UNREGISTER:
 		lock_sock(sk);
 
-		/* remove device specific receive entries */
+		/* rx_ops: remove device specific receive entries */
 		list_for_each_entry(op, &bo->rx_ops, list)
 			if (op->rx_reg_dev == dev)
 				bcm_rx_unreg(dev, op);
 
+		/* tx_ops: stop device specific cyclic transmissions on the
+		 * vanishing ifindex. Cancelling the timer is enough to stop
+		 * cyclic bcm_can_tx() calls as there is no re-arming.
+		 */
+		list_for_each_entry(op, &bo->tx_ops, list)
+			if (op->ifindex == dev->ifindex)
+				hrtimer_cancel(&op->timer);
+
 		/* remove device reference, if this is our bound device */
 		if (bo->bound && bo->ifindex == dev->ifindex) {
 #if IS_ENABLED(CONFIG_PROC_FS)
-- 
2.53.0