[PATCH v14 09/11] can: bcm: fix stale rx/tx ops after device removal

From: Oliver Hartkopp <[email protected]>

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: [email protected]
Link: https://lore.kernel.org/linux-can/[email protected]/
Link: https://lore.kernel.org/linux-can/[email protected]/
Fixes: ffd980f976e7 ("[CAN]: Add broadcast manager (bcm) protocol")
Signed-off-by: Oliver Hartkopp <[email protected]>
---
 net/can/bcm.c | 52 +++++++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 43 insertions(+), 9 deletions(-)

diff --git a/net/can/bcm.c b/net/can/bcm.c
index 80ff3de66836..55226e5fec07 100644
--- a/net/can/bcm.c
+++ b/net/can/bcm.c
@@ -1277,10 +1277,11 @@ static int bcm_rx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
 			int ifindex, struct sock *sk)
 {
 	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))) {
 		/* be robust against wrong usage ... */
 		msg_head->flags |= RX_FILTER_ID;
@@ -1353,12 +1354,19 @@ static int bcm_rx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
 		spin_unlock_bh(&op->bcm_rx_update_lock);
 
 		/* 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 */
 		op = kzalloc(OPSIZ, GFP_KERNEL);
 		if (!op)
@@ -1421,10 +1429,11 @@ static int bcm_rx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
 		hrtimer_setup(&op->thrtimer, bcm_rx_thr_handler, CLOCK_MONOTONIC,
 			      HRTIMER_MODE_REL_SOFT);
 
 		/* call can_rx_register() */
 		do_rx_register = 1;
+		new_op = 1;
 
 	} /* if ((op = bcm_find_op(&bo->rx_ops, msg_head->can_id, ifindex))) */
 
 	/* check flags */
 
@@ -1462,11 +1471,14 @@ static int bcm_rx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
 		if ((op->flags & STARTTIMER) && op->kt_ival1)
 			hrtimer_start(&op->timer, op->kt_ival1,
 				      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;
 
 			dev = dev_get_by_index(sock_net(sk), ifindex);
@@ -1494,22 +1506,36 @@ static int bcm_rx_setup(struct bcm_msg_head *msg_head, struct msghdr *msg,
 				 * silently succeed without registering
 				 */
 				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;
 
 free_op:
@@ -1725,15 +1751,23 @@ static void bcm_notify(struct bcm_sock *bo, unsigned long msg,
 	switch (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)
 			if (sock_net(sk)->can.bcmproc_dir && bo->bcm_proc_read) {
 				remove_proc_entry(bo->procname, sock_net(sk)->can.bcmproc_dir);

-- 
2.53.0